This document is comprised of two parts. The first is this prospectus supplement, which describes the specific terms of this offering. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. This prospectus supplement also adds to, updates and changes information contained in the accompanying prospectus. If the information set forth in this prospectus supplement differs in any way from the information in the accompanying prospectus, you should rely on the information in this prospectus supplement. If the information set forth in this prospectus supplement conflicts with any statement in a document we have incorporated by reference, then you should consider only the statement in the more recent document.

The accompanying prospectus is part of a registration statement that we filed with the Securities and Exchange Commission (the “SEC”) using a shelf registration statement. Under the shelf registration process, from time to time, we may offer and sell debt securities, including the subordinated debt securities offered hereby, preferred shares, depositary shares, common stock, warrants, purchase contracts or units, or any combination thereof, in one or more offerings.

It is important that you read and consider all of the information contained in this prospectus supplement, the accompanying prospectus and any free writing prospectus filed by us with the SEC related to this offering in making your investment decision. You should also read and consider the information in the documents to which we have referred you in “Incorporation of Certain Documents by Reference” on page S-iii of this prospectus supplement and “Where You Can Find More Information” on page 2 of the accompanying prospectus.

We have not, and the underwriters have not, authorized any other person to provide you with any information other than the information contained in this prospectus supplement, the accompanying prospectus, any free writing prospectus we may authorize to be delivered to you and the documents incorporated by reference herein and therein. Neither we nor the underwriters take responsibility for, or provide any assurance as to the reliability of, any different or additional information. This prospectus supplement, the accompanying prospectus and any free writing prospectus do not constitute, and may not be used in connection with, an offer or solicitation by anyone in any jurisdiction in which such offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation. The information contained in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein or therein or any free writing prospectus prepared by us is only accurate as of the date of the document containing such information, regardless of the time of delivery of this prospectus supplement and any sale of the subordinated notes. Our business, financial condition, results of operations and prospects may have changed since that date.

The information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus is not investment, legal or tax advice. You should consult your own legal counsel, accountants and other advisers for legal, tax, business, financial and related advice before investing in the subordinated notes.

The distribution of this prospectus supplement, the accompanying prospectus and any free writing prospectus and the offering of the subordinated notes in certain jurisdictions may be restricted by law. Persons into whose possession this prospectus supplement, the accompanying prospectus and any free writing prospectus come should inform themselves about and observe any such restrictions.

In this prospectus supplement, references to “NBT,” the “Company,” “we,” “our” and “us” and similar terms mean NBT Bancorp Inc. and its subsidiaries, unless the context otherwise requires.

We expect that delivery of the subordinated notes will be made against payment therefor on or about June 23, 2020, which will be the fifth business day following the date of pricing of the subordinated notes, or “T+5.” Under Rule 15c6-1 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), trades in the secondary market generally are required to settle in two business days, unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the subordinated notes on the date of pricing or the next two succeeding business days will be required, by virtue of the fact that the subordinated notes initially settle in T+5, to specify an alternate settlement arrangement at the time of any such trade to prevent a failed settlement. Purchasers of the subordinated notes who wish to trade the subordinated notes prior to their date of delivery hereunder should consult their advisors.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public on the SEC’s website at www.sec.gov and on the investor relations page of our website at www.nbtbancorp.com. Except for those SEC filings incorporated by reference in this prospectus supplement, the contents of our website are not part of this prospectus, and the reference to our website does not constitute incorporation by reference in this prospectus of the information contained at that website.

In this prospectus supplement and the accompanying prospectus, as permitted by law, we “incorporate by reference” information from other documents that we file with the SEC. This means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus supplement and the accompanying prospectus and should be read with the same care. When we update the information contained in documents that have been incorporated by reference by making future filings with the SEC, the information incorporated by reference in this prospectus supplement and the accompanying prospectus is considered to be automatically updated and superseded. In other words, in case of a conflict or inconsistency between information contained in this prospectus supplement and the accompanying prospectus and information incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later.

We incorporate by reference the following documents listed below:

In addition, all reports and other documents we subsequently file pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date of this prospectus supplement and the accompanying prospectus until we complete the offering of the subordinated notes offered by this prospectus supplement (other than any information furnished pursuant to Item 2.02 or Item 7.01 of any Current Report on Form 8-K, unless we specifically state in such Current Report that such information is to be considered “filed” under the Exchange Act or we incorporate it by reference into a filing under the Securities Act of 1933, as amended (the “Securities Act”), or the Exchange Act) will be deemed to be incorporated by reference in this prospectus supplement and the accompanying prospectus and to be part of this prospectus supplement and the accompanying prospectus from the date of the filing of such reports and documents.

Any statement contained in this prospectus supplement, the accompanying prospectus or in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this prospectus supplement and the accompanying prospectus to the extent that a statement contained in any subsequently filed document which is or is deemed to be incorporated by reference herein modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement and the accompanying prospectus.

We will provide to each person to whom a prospectus supplement is delivered, a copy of any or all of the information that has been incorporated by reference in the prospectus supplement but not delivered with the prospectus. You may request a copy of these filings, other than an exhibit to a filing unless that exhibit is specifically incorporated by reference into that filing, at no cost, by writing to or telephoning us at the following address:

In addition, these filings are available on our website at www.nbtbancorp.com. Please note that this website address is for textual reference only and the information on our website is not a part of, and is not incorporated into, this prospectus or any applicable prospectus supplement.

Certain statements in this filing and future filings by the Company with the SEC, in the Company’s press releases or other public or stockholder communications or in oral statements made with the approval of an authorized executive officer, contain forward-looking statements, as defined in the Private Securities Litigation Reform Act. These statements may be identified by the use of phrases such as “anticipate,” “believe,” “expect,” “forecasts,” “projects,” “will,” “can,” “would,” “should,” “could,” “may,” or other similar terms. There are a number of factors, many of which are beyond the Company’s control that could cause actual results to differ materially from those contemplated by the forward-looking statements. Factors that may cause actual results to differ materially from those contemplated by such forward-looking statements include, among others, the following possibilities: (1) local, regional, national and international economic conditions and the impact they may have on the Company and its customers and the Company’s assessment of that impact; (2) changes in the level of nonperforming assets and charge-offs; (3) changes in estimates of future reserve requirements based upon the periodic review thereof under relevant regulatory and accounting requirements; (4) the effects of and changes in trade and monetary and fiscal policies and laws, including the interest rate policies of the Federal Reserve Board (“FRB”); (5) inflation, interest rate, securities market and monetary fluctuations; (6) political instability; (7) acts of war or terrorism; (8) the timely development and acceptance of new products and services and perceived overall value of these products and services by users; (9) changes in consumer spending, borrowings and savings habits; (10) changes in the financial performance and/or condition of the Company’s borrowers; (11) technological changes; (12) acquisitions and integration of acquired businesses; (13) the ability to increase market share and control expenses; (14) changes in the competitive environment among financial holding companies; (15) the effect of changes in laws and regulations (including laws and regulations concerning taxes, banking, securities and insurance) with which the Company and its subsidiaries must comply, including those under the Dodd-Frank Act, Economic Growth, Regulatory Relief, Consumer Protection Act of 2018, Coronavirus Aid, Relief and Economic Security Act (“CARES Act”), and regulatory pronouncements around CARES Act; (16) the effect of changes in accounting policies and practices, as may be adopted by the regulatory agencies, as well as the Public Company Accounting Oversight Board, the Financial Accounting Standards Board (“FASB”) and other accounting standard setters; (17) changes in the Company’s organization, compensation and benefit plans; (18) the costs and effects of legal and regulatory developments including the resolution of legal proceedings or regulatory or other governmental inquiries and the results of regulatory examinations or reviews; (19) greater than expected costs or difficulties related to the integration of new products and lines of business; (20) the adverse impact on the U.S. economy, including the markets in which we operate, of the novel coronavirus, which causes the Coronavirus disease 2019 (“COVID-19”), global pandemic; (21) the impact of a slowing U.S. economy and increased unemployment on the performance of our loan portfolio, the market value of our investment securities, the availability of sources of funding and the demand for our products; and (22) the Company’s success at managing the risks involved in the foregoing items.

Currently, one of the most significant factors that could cause actual outcomes to differ materially from the Company’s forward-looking statements is the potential adverse effect of the current COVID-19 pandemic on the financial condition, results of operations, cash flows and performance of the Company, its customers and the global economy and financial markets. The extent to which the COVID-19 pandemic impacts the Company will depend on future developments, which are highly uncertain and cannot be predicted with confidence, including the scope, severity and duration of the pandemic and its impact on the Company’s customers and demand for financial services, the actions governments, businesses and individuals take in response to the pandemic, the impact of the COVID-19 pandemic and actions taken in response to the pandemic on global and regional economies, national and local economic activity, and the pace of recovery when the COVID-19 pandemic subsides, among others. Moreover, investors are cautioned to interpret many of the risks identified under the section entitled “Risk Factors” in our Form 10-K for the year ended December 31, 2019 and in our Form 10-Q for the quarter ended March 31, 2020, both of which are incorporated herein by reference, as being heightened as a result of the ongoing and numerous adverse impacts of the COVID-19 pandemic.

The Company cautions readers not to place undue reliance on any forward-looking statements, which speak only as of the date made, and advises readers that various factors including, but not limited to, those described above and other factors discussed in the Company’s annual and quarterly reports previously filed with the SEC, could affect the Company’s financial performance and could cause the Company’s actual results or circumstances for future periods to differ materially from those anticipated or projected.

Unless required by law, we do not undertake, and specifically disclaim any obligations to, publicly release any revisions that may be made to any forward-looking statements to reflect the occurrence of anticipated or unanticipated events or circumstances after the date of such statements.

An investment in the subordinated notes involves certain risks. You should carefully consider the risk factors and other information included or incorporated by reference in this prospectus supplement and the accompanying prospectus before making an investment decision. In particular, you should carefully consider, among other things, the matters discussed below and under “Risk Factors” in our Annual Report on Form 10-K for the fiscal year ended December 31, 2019 and in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2020. Our business, financial condition and results of operations could be materially adversely affected by any of these risks. The price of the subordinated notes could decline due to any of these risks, and you may lose all or part of your investment. This prospectus supplement and the accompanying prospectus also contain forward-looking statements that involve risks and uncertainties. Our actual results could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks faced by us described below and elsewhere in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein. The prospectus supplement is qualified in its entirety by those risk factors.

The Company’s business is dependent upon the willingness and ability of our employees and customers to conduct banking and other financial transactions. The COVID-19 global public health crisis and the resulting “stay-at-home” orders have resulted in widespread volatility, severe disruptions in the U.S. economy at large, and for small businesses in particular, and deterioration in household, business, economic and market conditions. The extent of the impact of the COVID-19 pandemic and actions taken in response to the pandemic on our capital, liquidity and other financial positions and on our business, results of operations and prospects will depend on a number of evolving factors, including:

Additionally, if the COVID-19 pandemic has an adverse effect on (i) customer deposits, (ii) the ability of our borrowers to satisfy their obligations to us, (iii) the demand for our loans or our other products and services, (iv) other aspects of our business operations, or (v) on financial markets, real estate markets, or economic growth, this could, depending on the extent of the decline in customer deposits or loan defaults, materially and adversely affect our liquidity and financial condition and our results of operations could be materially and adversely affected.

The Company is unable to estimate the impact of the COVID-19 pandemic on our business and operations at this time. The global pandemic could cause us to experience higher credit losses in our lending portfolio, impairment of our goodwill and other financial assets, further reduce demand for our products and services and other negative impacts on our financial position, results of operations and prospects. Sustained adverse effects may also prevent us from satisfying our minimum regulatory capital ratios and other supervisory requirements or result in downgrades in our credit ratings.

Any of the negative impacts of the COVID-19 pandemic, including those described above, alone or in combination with others, may have a material adverse effect on our results of operations, financial condition and cash flows. Any of these negative impacts, alone or in combination with others, could exacerbate many of the risk factors discussed in Part I, “Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2019 incorporated by reference herein. The full extent to which the COVID-19 pandemic will negatively affect our results of operations, financial condition and cash flows will depend on future developments that are highly uncertain and cannot be predicted, including the scope and duration of the pandemic and actions taken by governmental authorities and other third parties in response to the pandemic.

The COVID-19 pandemic has significantly affected the financial markets and has resulted in a number of Federal Reserve actions. Market interest rates have declined significantly. On March 3, 2020, the 10-year Treasury yield fell below 1.00% for the first time, and the Federal Reserve reduced the target federal funds rate by 50 basis points to a range of 1.00% to 1.25%. On March 15, 2020, the Federal Reserve further reduced the target federal funds rate by 100 basis points to a range of 0.00% to 0.25% and announced a $700 billion quantitative easing program in response to the expected economic downturn caused by the COVID-19 pandemic. The Federal Reserve reduced the interest that it pays on excess reserves from 1.60% to 1.10% on March 3, 2020, and then to 0.10% on March 15, 2020. We expect that these reductions in interest rates, especially if prolonged, could adversely affect our net interest income and margins and our profitability.

Given our business mix, and the fact that most of our assets and liabilities are financial in nature, we tend to be sensitive to market interest rate movements and the performance of the financial markets. Our earnings and financial condition is largely dependent on net interest income, which is the difference between the interest earned from loans and investments and interest paid on deposits and borrowings. Prevailing economic conditions, fiscal and monetary policies and the policies of various regulatory agencies all affect market rates of interest and the availability and cost of credit, which, in turn, significantly affect financial institutions’ net interest income. If the interest we pay on deposits and other borrowings increases at a faster rate than increases in the interest we receive on loans and investments, net interest income, and, therefore, our earnings, could be affected. Earnings could also be affected if the interest we receive on loans and other investments falls more quickly than the interest we pay on deposits and other borrowings.

In addition to the general impact of the economy, changes in interest rates or in valuations in the debt or equity markets could directly impact us in one or more of the following ways:

In addition, the continued spread of COVID-19 has also led to disruption and volatility in financial markets, which could increase our cost of capital and adversely affect our ability to access financial markets, which may in turn affect the value of the subordinated notes. In addition, in March 2020, Moody’s Investor Services downgraded its outlook on U.S. banks to “negative” from “stable” due in part to the concerns presented by the coronavirus pandemic. This market volatility has resulted in a significant decline, and we may continue to experience further declines, in our stock price and market capitalization, which could result in goodwill impairment charges.

We offer a variety of secured loans, including commercial lines of credit, commercial term loans, real estate, construction, home equity, consumer and other loans. Many of our loans are secured by real estate (both residential and commercial) within our market area. A major change in the real estate market, such as deterioration in the value of collateral, or in the local or national economy, could affect our customers’ ability to pay these loans, which in turn could impact our results of operations and financial condition. Additionally, increases in unemployment also may affect the ability of certain clients to repay loans and the financial results of commercial clients in localities with higher unemployment, may result in loan defaults and foreclosures and may impair the value of our collateral. Additionally, a concentration of natural disasters or a significant disruption in the insurance market could impact the risk relating to our insurance lending business. We cannot fully eliminate credit risk, and as a result, credit losses may increase in the future.

The sharp deterioration in the United States economy that has resulted from the COVID-19 virus and the actions taken by the federal and state governments to slow the spread of that virus have resulted in a significant increase in the unemployment rate throughout the United States, including in the local economies in which we conduct business. We anticipate that this increase in unemployment will affect the ability of some of our clients to repay their loans on a timely basis and will adversely affect the financial results of our commercial clients in localities with high unemployment, resulting in loan defaults and the possible impairments in the value of our collateral. These developments could adversely impact our results of operations and financial condition, although the extent of such impact cannot be determined at this time and may be muted by NBT Bank’s implementation of hardship relief programs that include payment deferral and short-term funding options.

Like all financial institutions, we maintain an allowance for credit losses to provide for loans in our portfolio that may not be repaid in their entirety. Our allowance for credit losses may not be sufficient to cover actual loan losses, and future provision for credit losses could materially and adversely affect our operating results. The accounting measurements related to impairment and the allowance for credit losses require significant estimates which are subject to uncertainty and change related to new information and changing circumstances. Our estimates of the risk of loss and amount of loss on any loan are complicated by the significant uncertainties surrounding our borrowers’ abilities to successfully execute their business models through changing economic environments, competitive challenges and other factors. Because of the degree of uncertainty and susceptibility of these factors to change, our actual losses may vary from our current estimates.

Our regulators, as an integral part of their examination process, periodically review our allowance for credit losses and may require us to increase our allowance for credit losses by recognizing additional provision for losses charged to expense, or to decrease our allowance for credit losses by recognizing loan charge-offs, net of recoveries. Any such additional provision for loan losses or charge-offs, as required by these regulatory agencies, could have a material effect on our financial condition and results of operations.

As discussed under “Summary—Recent Developments” above, we adopted CECL in the first quarter of 2020, including the regulatory phase-in. As a result, credit loss allowances for loans increased from the January 1, 2020 adoption date to the March 31, 2020 quarter end, by approximately $24 million, resulting in a corresponding tax-effected decrease in retained earnings but a delayed impact to regulatory capital, as the Company adopted the regulatory capital transition relief over the permissible five-year period. CECL implementation poses operational risk, including the failure to properly transition internal processes or systems, which could lead to errors, financial misstatements or operational losses. As a result of CECL, our financial results may be negatively affected as soon as weak or deteriorating economic conditions are forecasted and alter our expectations for credit losses. Primarily as a result of COVID-19, our provision expense increased $24 million in the first quarter of 2020 from the first quarter of 2019, and we may incur significant provision expense for credit losses in future periods as well.

On March 27, 2020, President Trump signed the CARES Act, which included a $349 billion loan program administered through the SBA referred to as the PPP. Congress subsequently approved $321 billion in additional funding for the PPP, including $60 billion earmarked for community banks and other small lenders. Under the PPP, small businesses and other entities and individuals can apply for loans from existing SBA lenders and other approved regulated lenders that enroll in the program, subject to numerous limitations and eligibility criteria. The Company’s subsidiary, NBT Bank, is participating as a lender in the PPP. The PPP opened on April 3, 2020; however, because of the short timeframe between passage of the CARES Act and the opening of the PPP, there is some ambiguity in the laws, rules and guidance regarding the operation of the PPP and documentation of PPP loans, which could expose the Company to risks relating to noncompliance with the PPP. For example, as a PPP lender, the Company has credit risk on PPP loans if a determination is made by the SBA that there was a deficiency in the manner in which the loan was originated, funded, or serviced by NBT Bank, such as an issue with the eligibility of a borrower to receive a PPP loan, which may or may not be related to the ambiguity in the laws, rules and guidance regarding the operation of the PPP. In the event of a loss resulting from a default on a PPP loan and a determination by the SBA that there was a deficiency in the manner in which the PPP loan was originated, funded, or serviced by the Company, the SBA may deny its liability under the loan guaranty, reduce the amount of the guaranty, or, if it has already paid under the guaranty, seek recovery of any loss related to the deficiency from the Company. If any such deficiency or noncompliance with PPP requirements is systemic to all or a substantial portion of the Company’s PPP loan portfolio, the Company’s credit risk exposure could be significant. In addition, since inception of the PPP, several banks have been subject to litigation regarding their processes and procedures used in processing PPP loan applications. The Company could be exposed to similar risk of litigation, from both customers and non-customers who sought PPP loans from us, regarding our processes and procedures for processing PPP loan applications. Any such litigation, regardless of the outcome, could result in significant financial liability or adversely affect the Company’s reputation. In addition, the PPP may also attract significant interest from federal and state enforcement authorities, oversight agencies, regulators and Congressional committees. State Attorneys General and other federal and state agencies may assert that they are not subject to the provisions of the CARES Act and the PPP regulations that entitled NBT Bank to rely on borrower certifications, and take more aggressive action against NBT Bank for alleged violations of the provisions governing NBT Bank’s participation in the PPP.

The interest rate during the floating rate period will be determined using Three-Month Term SOFR (unless a Benchmark Transition Event and its related Benchmark Replacement Date occur with respect to Three-Month Term SOFR, in which case the rate of interest will be based on the next-available Benchmark Replacement). In the following discussion of the Secured Overnight Financing Rate (“SOFR”), when we refer to SOFR-linked subordinated notes, we mean the subordinated notes at any time when the interest rate on the subordinated notes is or will be determined based on SOFR, including Three-Month Term SOFR.

SOFR is published by the Federal Reserve Bank of New York (“FRBNY”) and is intended to be a broad measure of the cost of borrowing cash overnight collateralized by U.S. Treasury securities. FRBNY reports that SOFR includes all trades in the Broad General Collateral Rate, plus bilateral U.S. Treasury repurchase agreement (“repo”) transactions cleared through the delivery-versus-payment service offered by the Fixed Income Clearing Corporation (the “FICC”), a subsidiary of The Depository Trust & Clearing Corporation (“DTCC”). SOFR is filtered by FRBNY to remove a portion of the foregoing transactions considered to be “specials.” According to FRBNY, “specials” are repos for specific-issue collateral which take place at cash-lending rates below those for general collateral repos because cash providers are willing to accept a lesser return on their cash in order to obtain a particular security.

FRBNY reports that SOFR is calculated as a volume-weighted median of transaction-level tri-party repo data collected from The Bank of New York Mellon, which currently acts as the clearing bank for the tri-party repo market, as well as general collateral finance repo transaction data and data on bilateral U.S. Treasury repo transactions cleared through the FICC’s delivery-versus-payment service.

FRBNY states that it obtains information from DTCC Solutions LLC, an affiliate of DTCC. FRBNY currently publishes SOFR daily on its website at https://apps.newyorkfed.org/markets/autorates/sofr. FRBNY states on its publication page for SOFR that use of SOFR is subject to important disclaimers, limitations and indemnification obligations, including that FRBNY may alter the methods of calculation, publication schedule, rate revision practices or availability of SOFR at any time without notice. The foregoing Internet website is an inactive textual reference only, meaning that the information contained on the website is not part of this prospectus supplement or the accompanying prospectus or incorporated by reference herein or therein.

FRBNY started publishing SOFR in April 2018. FRBNY has also started publishing historical indicative SOFRs dating back to 2014, although this historical indicative data inherently involves assumptions, estimates and approximations. You should not rely on this historical indicative data or on any historical changes or trends in SOFR as an indicator of the future performance of SOFR.

As the interest rate of the subordinated notes will be calculated based on SOFR from July 1, 2025 to, but excluding, the maturity date or earlier redemption date and since SOFR is a floating rate, the interest rate on the subordinated notes will vary on and after July 1, 2025. During this period, the subordinated notes will bear a floating interest rate set each quarterly interest period at a per annum rate equal to the Benchmark rate (which is expected to be Three-Month Term SOFR) plus a spread of 485 basis points; provided, that in the event the Benchmark rate is less than zero, then the Benchmark rate shall be deemed to be zero. The per annum interest rate that is determined on the relevant determination date will apply to the entire quarterly interest period following such determination date even if the Benchmark rate increases during that period.

Floating rate notes bear additional significant risks not associated with fixed rate debt securities. These risks include fluctuation of the interest rates and the possibility that you will receive an amount of interest that is lower than expected. We have no control over a number of matters, including economic, financial, and political events, that are important in determining the existence, magnitude, and longevity of market volatility and other risks and their impact on the value of, or payments made on, the floating rate subordinated notes.

Since the initial publication of SOFR, daily changes in the rate have, on occasion, been more volatile than daily changes in comparable benchmark or market rates, and SOFR over time may bear little or no relation to the historical actual or historical indicative data. In addition, the return on and value of the SOFR-linked subordinated notes may fluctuate more than floating rate securities that are linked to less volatile rates.

Because SOFR is published by FRBNY based on data received from other sources, we have no control over its determination, calculation or publication. There can be no assurance that SOFR will not be discontinued or fundamentally altered in a manner that is materially adverse to the interests of investors in the SOFR-linked subordinated notes. If the manner in which SOFR is calculated is changed, that change may result in a reduction in the amount of interest that accrues on the SOFR-linked subordinated notes, which may adversely affect the trading prices of the SOFR-linked subordinated notes. In addition, the interest rate on the SOFR-linked subordinated notes for any day will not be adjusted for any modification or amendment to SOFR for that day that FRBNY may publish if the interest rate for that day has already been determined prior to such publication. Further, if the Benchmark rate on the SOFR-linked subordinated notes during the floating rate period for any interest period declines to zero or becomes negative, interest will only accrue on the SOFR-linked subordinated notes at a rate equal to the spread of 4.85% per annum with respect to that interest period. There is no assurance that changes in SOFR could not have a material adverse effect on the yield on, value of and market for the SOFR-linked subordinated notes.

In June 2017, the Alternative Reference Rates Committee (the “ARRC”) convened by the Federal Reserve and FRBNY announced SOFR as its recommended alternative to the London interbank offered rate for U.S. dollar obligations (“U.S. dollar LIBOR”). However, because SOFR is a broad U.S. Treasury repo financing rate that represents overnight secured funding transactions, it differs fundamentally from U.S. dollar LIBOR. For example,

SOFR is a secured overnight rate, while U.S. dollar LIBOR is an unsecured rate that represents interbank funding over different maturities. In addition, because SOFR is a transaction-based rate, it is backward-looking, whereas U.S. dollar LIBOR is forward-looking. Because of these and other differences, there can be no assurance that SOFR will perform in the same way as U.S. dollar LIBOR would have done at any time, and there is no guarantee that it is a comparable substitute for U.S. dollar LIBOR.

SOFR may fail to gain market acceptance. SOFR was developed for use in certain U.S. dollar derivatives and other financial contracts as an alternative to U.S. dollar LIBOR in part because it is considered to be a good representation of general funding conditions in the overnight U.S. Treasury repo market. However, as a rate based on transactions secured by U.S. Treasury securities, it does not measure bank-specific credit risk and, as a result, is less likely to correlate with the unsecured short-term funding costs of banks. This may mean that market participants would not consider SOFR to be a suitable substitute or successor for all of the purposes for which U.S. dollar LIBOR historically has been used (including, without limitation, as a representation of the unsecured short-term funding costs of banks), which may, in turn, lessen its market acceptance. Any failure of SOFR to gain market acceptance could adversely affect the return on, value of and market for the SOFR-linked subordinated notes.

Since SOFR is a relatively new market index, SOFR-linked debt securities likely will have no established trading market when issued, and an established trading market for the SOFR-linked subordinated notes may never develop or may not be very liquid. Market terms for securities that are linked to SOFR, such as the spread over the base rate reflected in the interest rate provisions, may evolve over time, and as a result, trading prices of the SOFR-linked subordinated notes may be lower than those of later-issued securities that are linked to SOFR. Similarly, if SOFR does not prove to be widely used in securities that are similar or comparable to the SOFR-linked subordinated notes, the trading price of the SOFR-linked subordinated notes may be lower than those of securities that are linked to rates that are more widely used. You may not be able to sell the SOFR-linked subordinated notes at all or may not be able to sell the SOFR-linked subordinated notes at prices that will provide you with a yield comparable to similar investments that have a developed secondary market, and may consequently suffer from increased pricing volatility and market risk. The manner of adoption or application of reference rates based on SOFR in the bond and equity markets may differ materially compared with the application and adoption of SOFR in other markets, such as the derivatives and loan markets. You should carefully consider how any potential inconsistencies between the adoption of reference rates based on SOFR across these markets may impact any hedging or other financial arrangements which you may put in place in connection with any acquisition, holding or disposal of the SOFR-linked subordinated notes.

Under the terms of the subordinated notes, the interest rate on the subordinated notes for each interest period during the floating rate period will be based on Three-Month Term SOFR, a forward-looking term rate for a tenor of three months that will be based on SOFR (“Three-Month Term SOFR”). Three-Month Term SOFR does not currently exist and is currently being developed under the sponsorship of the ARRC. There is no assurance that the development of Three-Month Term SOFR, or any other forward-looking term rate based on SOFR, will be completed. Uncertainty surrounding the development of forward-looking term rates based on SOFR could have a material adverse effect on the return on, value of and market for the subordinated notes. If, at the commencement of the floating rate period for the subordinated notes, the Federal Reserve and/or the FRBNY, or a committee officially endorsed or convened by the Federal Reserve and/or the FRBNY or any successor thereto (“Relevant Governmental Body”) has not selected or recommended a forward-looking term rate for a tenor of three months based on SOFR, the development of a forward-looking term rate for a tenor of three months based on SOFR that has been recommended or selected by the Relevant Governmental Body is not complete or the calculation agent determines that the use of a forward-looking rate for a tenor of three months based on SOFR is not administratively feasible, then the next-available Benchmark Replacement under the benchmark transition provisions will be used to determine the interest rate on the subordinated notes during the floating rate period (unless a Benchmark Transition Event and its related Benchmark Replacement Date occur with respect to that next-available Benchmark Replacement).

Under the terms of the subordinated notes, the calculation agent is expressly authorized to make determinations, decisions or elections with respect to technical, administrative or operational matters that it decides are appropriate to reflect the use of Three-Month Term SOFR as the interest rate basis for the subordinated notes, which are defined in the terms of the subordinated notes as “Three-Month Term SOFR Conventions.” For example, assuming that a form of Three-Month Term SOFR is developed, it is not currently known how or by whom rates for Three-Month Term SOFR will be published. Accordingly, the calculation agent will need to determine the applicable Three-Month Term SOFR during the floating rate period. The calculation agent’s determination and implementation of any Three-Month Term SOFR Conventions could result in adverse consequences to the amount of interest that accrues on the subordinated notes during the floating rate period, which could adversely affect the return on, value of and market for the subordinated notes.

Under the benchmark transition provisions of the subordinated notes, if the calculation agent determines that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to Three-Month Term SOFR, then the interest rate on the subordinated notes during the floating rate period will be determined using the next-available Benchmark Replacement (which may include a related Benchmark Replacement Adjustment). However, the Benchmark Replacement may not be the economic equivalent of Three-Month Term SOFR. For example, Compounded SOFR, the first available Benchmark Replacement, is the compounded average of the daily Secured Overnight Financing Rates calculated in arrears, while Three-Month Term SOFR is intended to be a forward-looking rate with a tenor of three months. In addition, very limited market precedent exists for securities that use Compounded SOFR as the rate basis, and the method for calculating Compounded SOFR in those precedents varies. Further, the ISDA Fallback Rate, which is another Benchmark Replacement, has not yet been established and may change over time.

Under the benchmark transition provisions of the subordinated notes, if a particular Benchmark Replacement or Benchmark Replacement Adjustment cannot be determined, then the next-available Benchmark Replacement or Benchmark Replacement Adjustment will apply. These replacement rates and adjustments may be selected or formulated by (i) the Relevant Governmental Body (such as the ARRC), (ii) ISDA or (iii) in certain circumstances, the calculation agent. In addition, the benchmark transition provisions expressly authorize the calculation agent to make certain changes, which are defined in the terms of the subordinated notes as “Benchmark Replacement Conforming Changes,” with respect to, among other things, the determination of interest periods, and the timing and frequency of determining rates and making payments of interest. The application of a Benchmark Replacement and Benchmark Replacement Adjustment, and any implementation of Benchmark Replacement Conforming Changes, could result in adverse consequences to the amount of interest that accrues on the subordinated notes during the floating rate period, which could adversely affect the return on, value of and market for the subordinated notes. Further, there is no assurance that the characteristics of any Benchmark Replacement will be similar to the then-current Benchmark that it is replacing, or that any Benchmark Replacement will produce the economic equivalent of the then-current Benchmark that it is replacing.

Subject to the prior approval of the Federal Reserve, to the extent that such approval is then required, we may redeem the subordinated notes at our option (i) in whole or in part beginning with the interest payment date of July 1, 2025, and on any interest payment date thereafter. In addition, at any time at which any subordinated notes remain outstanding, subject to the prior approval of the Federal Reserve, to the extent that such approval is then required, we may redeem the subordinated notes in whole but not in part upon the occurrence of (i) a “Tier 2 Capital Event,” (ii) a “Tax Event” or (iii) if we are required to register as an investment company pursuant to the 1940 Act. In the event that we redeem the subordinated notes, holders of the subordinated notes will receive only the principal amount of the subordinated notes plus any accrued and unpaid interest to, but excluding, such earlier redemption date. If any redemption occurs, holders of the subordinated notes will not have the opportunity to continue to accrue and be paid

interest to the stated maturity date. Any such redemption may have the effect of reducing the income or return that you may receive on an investment in the subordinated notes by reducing the term of the investment. If this occurs, you may not be able to reinvest the proceeds at an interest rate comparable to the rate paid on the subordinated notes. See “Description of Subordinated Notes—Redemption.”

Our obligations under the subordinated notes will be unsecured and will rank junior to the following, unless, by their terms, the obligation ranks equal with, or junior to, the subordinated notes:

If we default on payments under any of these obligations that are senior to the subordinated notes, or if any of these senior obligations are accelerated or any judicial proceeding with respect to a default is pending, we will not be able to make payments on the subordinated notes, unless we cure the default. If we liquidate, go bankrupt or dissolve, we would be able to pay under the subordinated notes only after we have paid in full all of our liabilities that are senior to the subordinated notes. As of March 31, 2020, we had $8.5 billion of senior indebtedness outstanding on a consolidated basis. The Subordinated Indenture (as defined below) does not limit the amount of senior indebtedness that we may incur. For more information on the subordination of payments under the subordinated notes, see “Description of Subordinated Notes—Subordination.”

The subordinated notes are not obligations of, or guaranteed by, any of our subsidiaries or any third party. As a result, our right and the rights of our creditors, including holders of the subordinated notes, to participate in any distribution of assets of any of our subsidiaries upon its liquidation, reorganization or otherwise would be subject to the prior claims of creditors of that subsidiary. In the event of any such distribution of assets of our bank subsidiary, NBT Bank, the claims of depositors and other general or subordinated creditors of NBT Bank would be entitled to priority over our claims or the claims of holders of the subordinated notes. Accordingly, the subordinated notes are structurally subordinated to all of the existing and future liabilities and obligations of our subsidiaries. Claims on NBT Bank by creditors other than us include those by holders of our long-term debt and there are substantial obligations with respect to deposit liabilities and federal funds purchased, other short-term borrowings and various other financial obligations. As of March 31, 2020, we had $8.5 billion of senior indebtedness outstanding on a

consolidated basis, and NBT Bank had $7.9 billion of deposits, $430.7 million of Federal Home Loan Bank (“FHLB”) advances, $152.4 million of customer repurchase agreements and $30 million of federal funds purchased to which the subordinated notes will be structurally subordinated.

As a holding company, our principal source of funds to service our debt, including the subordinated notes, is dividends from our subsidiaries. For the year ended December 31, 2019, our interest expense on our debt obligations was $4.4 million (holding company only).

Federal and state banking regulations limit dividends from NBT Bank to us. Generally, banks are prohibited from paying dividends when doing so would cause them to fall below regulatory minimum capital levels. Additionally, limits exist on banks paying dividends in excess of net income for specified periods. The total amount available for payment of dividends by NBT Bank was approximately $129.5 million at March 31, 2020, based on NBT Bank maintaining enough capital to be considered well capitalized and other regulatory restrictions on subsidiary bank dividend payments. During the year ended December 31, 2019, NBT Bank paid dividends of $50.2 million to us. In addition, federal bank regulatory agencies have the authority to prohibit NBT Bank from engaging in unsafe or unsound practices in conducting its business. The payment of dividends or other transfers of funds to us, depending on the financial condition of NBT Bank, could be deemed an unsafe or unsound practice.

Dividend payments from NBT Bank would also be prohibited under the “prompt corrective action” regulations of federal bank regulators if NBT Bank is, or after payment of such dividends would be, undercapitalized under such regulations. In addition, NBT Bank is subject to restrictions under federal law that limit their ability to transfer funds or other items of value to us and our non-bank subsidiaries, including affiliates, whether in the form of loans and other extensions of credit, investments and asset purchases, or as other transactions involving the transfer of value. Unless an exemption applies, these transactions by NBT Bank with us are limited to 10% of NBT Bank’ capital stock and surplus and, with respect to all such transactions with affiliates in the aggregate, to 20% of NBT Bank’s capital stock and surplus. As of March 31, 2020, a maximum of approximately $129.5 million was available to us from NBT Bank pursuant to these limitations. Moreover, loans and extensions of credit by NBT Bank to its affiliates, including us, generally are required to be secured in specified amounts. A bank’s transactions with its non-bank affiliates also are required generally to be on arm’s-length terms. Accordingly, we can provide no assurance that we will receive dividends or other distributions from NBT Bank and our other subsidiaries in an amount sufficient to pay interest on or principal of the subordinated notes.

Payment of principal on the subordinated notes may be accelerated only in the case of certain events of bankruptcy or insolvency involving us or NBT Bank. There is no automatic acceleration, or right of acceleration, in the case of default in the payment of principal of or interest on the subordinated notes, or in the performance of any of our other obligations under the subordinated notes or the Subordinated Indenture governing the subordinated notes. Our regulators can, in the event we or NBT Bank become subject to an enforcement action, prohibit NBT Bank from paying dividends to us, and prevent our payment of interest or principal on the subordinated notes and any dividends on our capital stock, but such limits will not permit acceleration of the subordinated notes. See “Description of the Subordinated Notes—Events of Default.”

In addition to our currently outstanding indebtedness and any additional indebtedness we may incur pursuant to this offering, we may be able to borrow substantial additional indebtedness, including senior debt, in the future. If new indebtedness is incurred in addition to our current debt levels, the related risks that we now face could increase.

Our indebtedness, including the indebtedness we may incur in the future, could have important consequences for the holders of the subordinated notes, including:

The Subordinated Indenture does not limit the incurrence of additional indebtedness by us, including secured indebtedness, which would be effectively senior to the subordinated notes to the extent of the value of the collateral securing such indebtedness.

Our ability to make payments on our indebtedness, including the subordinated notes, and to fund planned capital expenditures will depend on our ability to generate cash in the future. We cannot assure you that our business will generate sufficient cash flow from operations or that future borrowings will be available to us in an amount sufficient to enable us to pay interest on and principal of our indebtedness, including the subordinated notes, or to fund our other liquidity needs.

The covenants in the Subordinated Indenture governing the subordinated notes are limited. In addition, the subordinated notes and the Subordinated Indenture do not limit our or our subsidiaries’ ability to further issue additional subordinated notes, including additional notes of the same series as the subordinated notes, or to incur additional debt. As a result, the terms of the Subordinated Indenture do not protect you in the event of an adverse change in our financial condition or results of operations, and you should not consider the terms of the Subordinated Indenture to be a significant factor in evaluating whether we will be able to comply with our obligations under the subordinated notes.

The subordinated notes are a new issuance of securities with no established trading market. We do not intend to apply for listing of the subordinated notes on any national securities exchange or for quotation of the subordinated notes on any automated dealer quotation system. The underwriters have advised us that they presently intend to make a market in the subordinated notes. However, they are under no obligation to do so and may discontinue any market making activities at any time without any notice. A liquid or active trading market for the subordinated notes may not develop. If an active trading market for the subordinated notes does not develop, the market price and liquidity of the subordinated notes may be adversely affected. If the subordinated notes offered hereby are traded, they may trade at a discount from their initial offering price, depending on prevailing interest rates, the market for similar securities, our performance and other factors.

Many factors could affect the trading market for, and the trading value of, the subordinated notes. These factors include: the method of calculating the principal, premium, if any, interest or other amounts payable, if any, on the subordinated notes; the time remaining to the maturity of the subordinated notes; the ranking of the subordinated notes; the redemption features of the subordinated notes; the outstanding amount of subordinated notes with terms identical to the subordinated notes offered hereby; the prevailing interest rates being paid by other companies similar to us; changes in U.S. interest rates; whether the ratings on the subordinated notes or us provided by any rating agency have changed; our financial condition, financial performance and future prospects; the level, direction and volatility of market interest rates generally; general economic conditions of the capital markets in the United States; and

geopolitical conditions and other financial, political, regulatory, and judicial events that affect the capital markets generally. The condition of the financial markets and prevailing interest rates have fluctuated significantly in the past and are likely to fluctuate in the future. Such fluctuations could adversely affect the trading market (if any) for, and the market price of, the subordinated notes.

The subordinated notes are not savings accounts, deposits or other obligations of NBT Bank and are not insured by the FDIC or any other governmental agency or instrumentality.

Rating agencies continuously evaluate us and our subsidiaries, and their ratings of our and NBT Bank’s long-term and short-term debt are based on a number of factors, including financial strength, as well as factors not entirely within our and NBT Bank’s control, such as conditions affecting the financial services industry generally. In light of these reviews and the continued focus on the financial services industry generally, we and NBT Bank may not be able to maintain our current credit ratings. Ratings downgrades by a rating agency could have a significant and immediate impact on our funding and liquidity through cash obligations, reduced funding capacity and collateral triggers. A reduction in our or NBT Bank’s credit ratings could also increase our and NBT Bank’s borrowing costs and limit access to the capital markets.

Downgrades in the credit or financial strength ratings assigned to the counterparties with whom we transact could create the perception that our financial condition will be adversely impacted as a result of potential future defaults by such counterparties. Additionally, we could be adversely affected by a general, negative perception of financial institutions caused by the downgrade of other financial institutions. Accordingly, ratings downgrades for other financial institutions could affect the market price of our stock and could limit our access to or increase our cost of capital.

The calculation agent will determine the interest rate during the floating rate period. We will act as the initial calculation agent for the subordinated notes. Any exercise of discretion by us under the terms of the subordinated notes, including, without limitation, any discretion exercised by us acting as calculation agent, could present a conflict of interest. In making the required determinations, decisions and elections, we may have economic interests that are adverse to the interests of the holders of the subordinated notes, and those determinations, decisions or elections could have a material adverse effect on the yield on, value of and market for the subordinated notes. Any determination by us, as the calculation agent, will be final and binding absent manifest error.

The subordinated notes may be issued with OID for U.S. federal income tax purposes. In such case, holders subject to U.S. federal income taxation, whether on the cash or accrual method of tax accounting, generally would be required to include any amounts representing OID in gross income (as ordinary income) as the OID accrues on a constant yield to maturity basis, in advance of the receipt of cash payments to which such income is attributable. See “Certain U.S. Federal Income Tax Consequences.”

We expect to receive net proceeds from this offering of approximately $97.9 million after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds from this offering for general corporate purposes, which may include working capital, repaying indebtedness, providing capital to support the organic growth of NBT Bank and our other subsidiaries, financing investments and capital expenditures, funding acquisitions and for investments in NBT Bank and our other subsidiaries as regulatory capital.

The following table sets forth our consolidated capitalization as of March 31, 2020 (i) on an actual basis and (ii) on an as adjusted basis to give effect to the sale of $100,000,000 aggregate principal amount of subordinated notes offered hereby, after deducting the underwriting discount and estimated expenses. You should read this table in conjunction with the more detailed information, including our consolidated financial statements and related notes, incorporated by reference in this prospectus supplement and accompanying prospectus.

The following summary of the subordinated notes does not purport to be complete and is qualified in its entirety by the Subordinated Indenture (as defined below), including the definitions therein of certain terms. Unless otherwise specified, capitalized terms used in this summary have the meanings specified in the Subordinated Indenture. For purposes of this “Description of Subordinated Notes,” references to the “Company,” “NBT,” “we,” and “us” include only NBT Bancorp Inc. and not its consolidated subsidiaries.

The subordinated notes offered hereby will be issued under a subordinated indenture, dated as of June 23, 2020, as amended and supplemented by a first supplemental indenture, dated as of June 23, 2020, between NBT and U.S. Bank National Association, as trustee, which together we refer to in this summary as the “Subordinated Indenture.”

The subordinated notes will be our general unsecured, subordinated obligations and will rank equally with all of our other unsecured, subordinated obligations from time to time outstanding. The subordinated notes will rank junior to all of our existing and future Senior Indebtedness (as defined below) to the extent and in the manner set forth in the Subordinated Indenture. In addition, the subordinated notes will be effectively subordinated to all of our secured indebtedness to the extent of the value of the assets securing such indebtedness. The subordinated notes will be structurally subordinated to all of the existing and future liabilities and obligations of our subsidiaries, including the deposit liabilities and claims of other creditors of our subsidiary bank, NBT Bank. See “—Subordination.” The subordinated notes will be obligations of NBT Bancorp Inc. only and will not be obligations of, and will not be guaranteed by, any of our subsidiaries. The subordinated notes are not deposits and are not insured by the FDIC or any other governmental agency.

The subordinated notes will mature on July 1, 2030 (the “Maturity Date”), unless previously redeemed or otherwise accelerated. There is no sinking fund for the subordinated notes. We intend for the subordinated notes to qualify (subject to applicable limitations) as Tier 2 capital under applicable capital regulations, guidance, and interpretations of the Board of Governors of the Federal Reserve System (the “Federal Reserve”).

Beginning with the interest payment date of July 1, 2025, and on any interest payment date thereafter, we may, at our option, subject to obtaining the prior approval of the Federal Reserve to the extent such approval is then required under the rules of the Federal Reserve (or, as and if applicable, the rules of any successor appropriate bank regulatory agency) (“Federal Reserve Approval”), redeem the subordinated notes, in whole or in part, at a price equal to 100% of the principal amount of the subordinated notes to be redeemed plus any accrued and unpaid interest to, but excluding, the redemption date. The subordinated notes may not be redeemed by us prior to July 1, 2025, except that we may, at our option, subject to Federal Reserve Approval, redeem the subordinated notes in whole, but not in part, prior to maturity, including prior to July 1, 2025, upon the occurrence of a “Tax Event” or a “Tier 2 Capital Event” (as such terms are defined in the Subordinated Indenture) or if we are required to register as an investment company pursuant to the 1940 Act, in each case, at a price equal to 100% of the principal amount of the subordinated notes to be redeemed plus any accrued and unpaid interest to, but excluding, the redemption date. Any partial redemption will be made in accordance with the applicable procedures of The Depository Trust Company (with its successors, “DTC”). See “—Redemption.”

The subordinated notes will initially be limited to an aggregate principal amount of $100,000,000. We may in the future from time to time, without notice to or consent of the holders of the subordinated notes, create and issue additional subordinated notes having the same terms and conditions as the subordinated notes offered by this prospectus supplement in all respects, except for any differences in the issue date and price and interest accrued prior to the issue date of the additional subordinated notes; provided that no such additional subordinated notes may be issued unless they will be fungible for U.S. securities law purposes and (1) such additional subordinated notes are issued pursuant to a “qualified reopening” of the subordinated notes offered hereby for U.S. federal income tax purposes, or (2) such additional subordinated notes are, and the subordinated notes offered hereby were, issued without OID for U.S. federal income tax purposes; and provided, further, that the additional subordinated notes have the same CUSIP number as the subordinated notes offered hereby. The subordinated notes offered hereby and any additional subordinated notes would rank equally and ratably and would be treated as a single series for all purposes under the Subordinated Indenture. No additional subordinated notes may be issued if any event of default has occurred and is continuing with respect to the subordinated notes.

From and including the date of original issuance to, but excluding, July 1, 2025, or the date of earlier redemption (the “fixed rate period”), the subordinated notes will bear interest at a fixed rate of 5.000% per annum, payable semi-annually in arrears on January 1 and July 1 of each year (each, a “fixed rate interest payment date”), commencing on January 1, 2021. The last fixed rate interest payment date for the fixed rate period will be July 1, 2025.

From and including July 1, 2025, to, but excluding, the Maturity Date or the date of earlier redemption (the “floating rate period”), the subordinated notes will bear interest at a floating rate per annum equal to the Benchmark rate (which is expected to be Three-Month Term SOFR) plus a spread of 485 basis points. For each quarterly interest period during the floating rate period, interest will be payable quarterly in arrears on January 1, April 1, July 1, and October 1 of each year (each, a “floating rate interest payment date” and, together with the fixed rate interest payment dates, the “interest payment dates”), commencing on October 1, 2025. Notwithstanding the foregoing, if the Benchmark rate is less than zero, the Benchmark rate shall be deemed to be zero.

For the purpose of calculating the interest on the subordinated notes for each interest period during the floating rate period when the Benchmark is Three-Month Term SOFR, “Three-Month Term SOFR” means the rate for Term SOFR for a tenor of three months that is published by the Term SOFR Administrator at the Reference Time for any interest period, as determined by the calculation agent after giving effect to the Three-Month Term SOFR Conventions. We will act as the initial calculation agent.

The following definitions apply to the foregoing definition of Three-Month Term SOFR:

“Benchmark” means, initially, Three-Month Term SOFR; provided that if the calculation agent determines on or prior to the Reference Time that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to Three-Month Term SOFR or the then-current Benchmark, then “Benchmark” means the applicable Benchmark Replacement.

“Federal Reserve Bank of New York’s Website” means the website of the Federal Reserve Bank of New York at http://www.newyorkfed.org, or any successor source. The foregoing Internet website is an inactive textual reference only, meaning that the information contained on the website is not part of this prospectus supplement or the accompanying prospectus or incorporated by reference herein or therein.

“Reference Time” with respect to any determination of the Benchmark means (1) if the Benchmark is Three-Month Term SOFR, the time determined by the calculation agent after giving effect to the Three-Month Term SOFR Conventions, and (2) if the Benchmark is not Three-Month Term SOFR, the time determined by the calculation agent after giving effect to the Benchmark Replacement Conforming Changes.

“Relevant Governmental Body” means the Federal Reserve and/or the Federal Reserve Bank of New York, or a committee officially endorsed or convened by the Federal Reserve and/or the Federal Reserve Bank of New York or any successor thereto.

“SOFR” means the secured overnight financing rate published by the Federal Reserve Bank of New York, as the administrator of the Benchmark (or a successor administrator), on the Federal Reserve Bank of New York’s Website.

“Term SOFR” means the forward-looking term rate based on SOFR that has been selected or recommended by the Relevant Governmental Body.

“Term SOFR Administrator” means any entity designated by the Relevant Governmental Body as the administrator of Term SOFR (or a successor administrator).

“Three-Month Term SOFR Conventions” means any determination, decision or election with respect to any technical, administrative or operational matter (including with respect to the manner and timing of the publication of Three-Month Term SOFR, or changes to the definition of “interest period,” timing and frequency of determining Three-Month Term SOFR with respect to each interest period and making payments of interest, rounding of amounts or tenors, and other administrative matters) that the calculation agent decides may be appropriate to reflect the use of Three-Month Term SOFR as the Benchmark in a manner substantially consistent with market practice (or, if the calculation agent decides that adoption of any portion of such market practice is not administratively feasible or if the calculation agent determines that no market practice for the use of Three-Month Term SOFR exists, in such other manner as the calculation agent determines is reasonably necessary).

The terms “Benchmark Replacement,” “Benchmark Replacement Conforming Changes,” “Benchmark Replacement Date,” “Benchmark Transition Event” and “Corresponding Tenor” and have the meanings set forth below under the heading “—Effect of Benchmark Transition Event.”

Notwithstanding the foregoing paragraphs related to the determination of interest, if the calculation agent determines on or prior to the relevant Reference Time that a Benchmark Transition Event and its related Benchmark Replacement Date (each as defined below) have occurred with respect to Three-Month Term SOFR, then the provisions set forth below under the heading “—Effect of Benchmark Transition Event,” which we refer to as the “benchmark transition provisions,” will thereafter apply to all determinations of the interest rate on the subordinated notes for each interest period during the floating rate period. In accordance with the benchmark transition provisions, after a Benchmark Transition Event and its related Benchmark Replacement Date have occurred, the interest rate on the subordinated notes for each interest period during the floating rate period will be an annual rate equal to the Benchmark Replacement plus 485 basis points.

Absent manifest error, the calculation agent’s determination of the interest rate for an interest period for the subordinated notes will be binding and conclusive on you, the trustee and us. The calculation agent’s determination of any interest rate, and its calculation of interest payments for any period, will be maintained on file at the calculation agent’s principal offices, will be made available to any holder of the subordinated notes upon request and will be provided to the trustee.

Interest on the subordinated notes will be calculated on the basis of a 360-day year consisting of twelve 30-day months during the fixed rate period and on the basis of a 360-day year and the actual number of days elapsed during the floating rate period. Dollar amounts resulting from that calculation will be rounded to the nearest cent, with one half cent being rounded upward.

Interest on the subordinated notes, subject to certain exceptions, will accrue during the applicable interest period. When we use the term “interest period,” we mean the period from and including the immediately preceding interest payment date in respect of which interest has been paid or duly provided for or, if no interest has been paid or duly provided for, from and including the date of issuance of the subordinated notes to, but excluding, the applicable interest payment date or the Maturity Date or date of earlier redemption, if applicable. If a fixed rate interest payment date or the Maturity Date falls on a day that is not a business day, then the interest payment or the payment of principal and interest at maturity will be paid on the next succeeding business day, but the payments made on such dates will be treated as being made on the date that the payment was first due and the holders of the subordinated notes will not be entitled to any further interest or other payments. If a floating rate interest payment date falls on a day that is not a business day, then such floating rate interest payment date will be postponed to the next succeeding business day unless such day falls in the next succeeding calendar month, in which case such floating rate interest payment date will be accelerated to the immediately preceding business day, and, in each such case, the amounts payable on such business day will include interest accrued to, but excluding, such business day.

Interest on each subordinated note will be payable to the person in whose name such subordinated note is registered on the fifteenth day immediately preceding the applicable interest payment date, whether or not such day is a business day. Any interest which is payable, but is not punctually paid or duly provided for, on any interest payment date shall cease to be payable to the holder on the relevant record date by virtue of having been a holder on such date, and such defaulted interest may be paid by us to the person in whose name the subordinated notes are registered at the close of business on a special record date for the payment of defaulted interest, or in any other lawful manner not inconsistent with the requirements of any securities exchange on which the subordinated notes may be listed. However, interest that is paid on the Maturity Date will be paid to the person to whom the principal will be payable. Interest will be payable by wire transfer in immediately available funds in U.S. dollars at the office of the principal paying agent or, at our option in the event the subordinated notes are not represented by global notes, by check mailed to the address of the person specified for payment in the preceding sentences.

If the then-current Benchmark is Three-Month Term SOFR, the calculation agent will have the right to establish the Three-Month Term SOFR Conventions, and if any of the foregoing provisions concerning the calculation of the interest rate and interest payments during the floating rate period are inconsistent with any of the Three-Month Term SOFR Conventions determined by the calculation agent, then the relevant Three-Month Term SOFR Conventions will apply. Furthermore, if the calculation agent determines that a Benchmark Transition Event and its related

Benchmark Replacement Date have occurred with respect to Three-Month Term SOFR at any time when any of the subordinated notes are outstanding, then the foregoing provisions concerning the calculation of the interest rate and interest payments during the floating rate period will be modified in accordance with the benchmark transition provisions.

When we refer to a “business day” with respect to the subordinated notes, we mean any day, other than a Saturday or Sunday, that is neither a legal holiday nor a day on which the trustee or banking institutions in Norwich, New York or The City of New York are authorized or required by law, regulation or executive order to close.

The subordinated notes are our general unsecured, subordinated obligations and are:

The subordinated notes are junior in right of payment to the prior payment in full of all of our Senior Indebtedness. This means that, under certain circumstances where we may not be making payments on all of our debt obligations as they become due, the holders of all of our Senior Indebtedness will be entitled to receive payment in full of all amounts that are due or will become due on their debt securities before the holders of the subordinated notes will be entitled to receive any amounts under the subordinated notes.

The Subordinated Indenture does not restrict us or any of our subsidiaries in any way now or in the future from incurring any debt, whether Senior Indebtedness, secured debt or indebtedness that would be pari passu with or subordinate to the subordinated notes.

The Subordinated Indenture provides that, unless all principal of and any premium or interest on Senior Indebtedness has been paid in full, no payment or other distribution may be made in respect of any subordinated notes under the following circumstances:

If the trustee or any holders of subordinated notes receives any payment or distribution that is prohibited under the subordination provisions, such payment or distribution shall be held in trust for and so paid and delivered to the holders of Senior Indebtedness (or their duly authorized representatives) until all Senior Indebtedness shall have been paid in full.

Even if the subordination provisions prevent us from making any payment when due on the subordinated notes, we will be in default on our obligations under the subordinated notes if we do not make the payment when due. This means that the trustee and the holders of subordinated notes can take action against us, but they will not receive any money until the claims of the holders of Senior Indebtedness have been fully satisfied.

The Subordinated Indenture defines “Senior Indebtedness” as:

unless, in any case in the instrument creating or evidencing any such indebtedness or obligation, or pursuant to which the same is outstanding, it is provided that such indebtedness or obligation is not superior in right of payment to the subordinated notes or to other debt that is pari passu with or subordinate to the subordinated notes.

Senior Indebtedness does not include:

As of March 31, 2020, we had $8.5 billion of Senior Indebtedness outstanding on a consolidated basis.

We are a financial holding company and substantially all of our assets are held by our direct and indirect subsidiaries. We rely on dividends and other payments or distributions from our subsidiaries to pay the interest on our debt obligations (such as the subordinated notes offered hereby), which interest expense was $4.4 million and $4.1 million for each of the years ended December 31, 2019 and 2018, respectively (holding company only). Federal and state bank regulations impose certain restrictions on the ability of our bank subsidiaries to pay dividends directly or indirectly to us, to make any extensions of credit to us or certain of our affiliates and to invest in our stock or securities. These regulations also prevent us from borrowing from our bank subsidiaries unless the loans are secured by collateral. Accordingly, we may not have access to sufficient cash to make payments on the subordinated notes. See “Risk Factors.”

Because we are a holding company, our rights and the rights of our creditors, including holders of the subordinated notes, to participate in any distribution of assets of any of our subsidiaries upon the liquidation, reorganization, dissolution or winding up of any of our subsidiaries will be structurally subordinated to all existing and future liabilities of such subsidiary and, as such, would be subject to the prior claims of the creditors of such subsidiary (except to the extent that we are a creditor with a recognized claim). In the event of any such distribution of assets of NBT Bank due in part to its status as an insured depository institution, the claims of its depositors and other general or subordinated creditors would be entitled to priority over claims of its stockholder, including us as

its parent holding company and any creditor of ours, such as holders of the subordinated notes. As of March 31, 2020, NBT Bank had $7.9 billion of deposits, $430.7 million of FHLB advances, $152.4 million of customer repurchase agreements and $30 million of federal funds purchased to which the subordinated notes will be structurally subordinated.

In the event that any payment on the subordinated notes is subject to withholding of any U.S. federal income tax or other tax or assessment (as a result of a change in law or otherwise), we will not pay additional amounts with respect to such tax or assessment. For a discussion relating to certain U.S. federal income tax consequences of the ownership and disposition of the subordinated notes, see “Certain U.S. Federal Income Tax Consequences.”

We may, at our option, beginning with the interest payment date of July 1, 2025, but not prior thereto (except upon the occurrence of certain events specified below), and on any interest payment date thereafter, redeem the subordinated notes, in whole or in part, from time to time, subject to obtaining the Federal Reserve Approval, at a price equal to 100% of the principal amount of the subordinated notes being redeemed plus accrued and unpaid interest to, but excluding, the date of redemption.

The subordinated notes may not otherwise be redeemed prior to the Maturity Date, except that we may also, at our option, redeem the subordinated notes, in whole, but not in part, subject to obtaining the Federal Reserve Approval, at a redemption price equal to 100% of the principal amount of the subordinated notes being redeemed plus accrued and unpaid interest to, but excluding, the date of redemption, at any time, including before July 1, 2025, upon the occurrence of:

In the event of any redemption of the subordinated notes, we will deliver or cause to be delivered a notice of redemption (which notice may be conditional in our discretion on one or more conditions precedent, and the redemption date may be delayed until such time as any or all of such conditions have been satisfied or revoked by us if we determine that such conditions will not be satisfied) to each holder of subordinated notes not less than 30 nor more than 60 days prior to the redemption date. We will provide written notice to the trustee prior to the close of business two business days prior to the redemption date (or such shorter period as may be acceptable to the trustee) if any such redemption has been rescinded or delayed, and upon receipt the trustee will provide such notice to each holder of the notes in the same manner in which the notice of redemption was given.

Any partial redemption will be made in accordance with the Depository Trust Company (“DTC”)’s applicable procedures among all of the holders of the subordinated notes. If any subordinated note is to be redeemed in part only, the notice of redemption relating to such subordinated note shall state the portion of the principal amount thereof to be redeemed. A replacement subordinated note in principal amount equal to the unredeemed portion thereof will be issued in the name of the holder thereof upon cancellation of the original note. The subordinated notes are not subject to redemption or prepayment at the option of the holders.

Under the Subordinated Indenture, an event of default permitting acceleration of the maturity of the subordinated notes will occur with respect to the subordinated notes only upon our or our principal subsidiary bank’s bankruptcy, insolvency, liquidation, reorganization or similar event. The term “principal subsidiary bank” means each of (1) any bank subsidiary the consolidated assets of which constitute 40% or more of our consolidated assets and (2) any other bank subsidiary designated as a “principal subsidiary bank” by our Board of Directors; provided that if the Federal Reserve notifies us that our bank subsidiary that is a principal subsidiary bank applying the tests in clause (1) or (2) above does not qualify as a “major subsidiary depository institution” within the requirements of the Federal Reserve’s capital guidelines applicable to bank holding companies, such bank subsidiary will not be a principal subsidiary bank from and after the time we receive from the Federal Reserve such a notice. Currently, NBT Bank is our only principal subsidiary bank and therefore is a “principal subsidiary bank.” If an event of default permitting acceleration of the maturity of the subordinated notes occurs and is continuing, either the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding subordinated notes may declare the principal amount and interest to be due and payable immediately. The foregoing provision would, in the event of the bankruptcy or insolvency involving the Company or NBT Bank, be subject as to enforcement to the broad equity powers of a federal bankruptcy court and to the determination by that court of the nature and status of the payment claims of the holders of the subordinated notes.

If we default in our obligation to pay any interest on the subordinated notes when due and payable and such default continues for a period of 30 days, or if we default in our obligation to pay the principal amount due upon maturity, and such default continues for a period of 30 days, then the trustee may, subject to certain limitations and conditions, seek to enforce its rights and the rights of the holders of subordinated notes of the performance of any covenant or agreement in the Subordinated Indenture. The trustee and holders of the subordinated notes may not accelerate the maturity of the subordinated notes, except upon our or our principal subsidiary bank’s bankruptcy, insolvency, liquidation, receivership or similar event.

The Subordinated Indenture also provides that the holders of not less than a majority in principal amount of the subordinated notes may waive any past default with respect to the subordinated notes and its consequences, except a default consisting of:

The Subordinated Indenture contains a provision entitling the trustee to be indemnified by the holders of any outstanding subordinated notes before proceeding to exercise any right or power under the Subordinated Indenture at the holders’ request or direction. The holders of a majority in principal amount of outstanding subordinated notes of a series may direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or other power conferred on the trustee, with respect to the subordinated notes of that series. However, the trustee may refuse to follow any direction which is in conflict with any law or the Subordinated

Indenture, which may involve the trustee in personal liability or which may be unduly prejudicial to the holders of the subordinated notes not joining in the direction (it being understood that the trustee does not have an affirmative duty to ascertain whether or not any such directions are unduly prejudicial to such holders).

The Subordinated Indenture provides that no holder of the subordinated notes will have any right to institute any proceeding, judicial or otherwise, with respect to the Subordinated Indenture, or for the appointment of a receiver or trustee, or for any other remedy hereunder, unless:

These limitations do not apply to a suit instituted by a holder of subordinated notes for the enforcement of payment of the principal of or interest on the subordinated notes on or after the maturity date.

Except as set forth below, modification and amendment of the Subordinated Indenture as applicable to the subordinated notes may be made only with the consent of the holders of not less than a majority in principal amount of the subordinated notes and all other series of debt securities issued under the Subordinated Indenture and affected by such modification or amendment (voting as one class).

No modification or amendment of the Subordinated Indenture as applicable to the subordinated notes may, without the consent of each holder affected thereby, do any of the following:

We and the trustee may modify or amend the Subordinated Indenture as applicable to the subordinated notes, without the consent of any holder of the subordinated notes, for any of the following purposes:

No modification or amendment of the Subordinated Indenture that adversely affects the superior position of any holder of senior indebtedness will be effective against any such holder of senior indebtedness unless such holder of senior indebtedness will have consented to such modification or amendment.

We may consolidate with or merge into any other corporation, or convey or transfer our properties and assets substantially as an entirety to any person or entity, provided that:

Upon any such consolidation or merger, or conveyance or transfer, the successor corporation formed, or into which we are merged or to which such conveyance or transfer is made, shall succeed to, and be substituted for, us under the Subordinated Indenture, as supplemented.

This covenant would not apply to any recapitalization transaction, change of control of us or a transaction in which we incur a large amount of additional debt unless the transaction or change of control included a merger or consolidation or transfer of all or substantially all of our assets. There are no covenants or other provisions in the

Subordinated Indenture providing for a put option or increased interest or that would otherwise afford holders of the subordinated notes additional protection in the event of a recapitalization transaction, a change of control of us or a transaction in which we incur or acquire a large amount of additional debt.

Although there is a limited body of case law interpreting the phrase “substantially as an entirety” and similar phrases, there is no precise established definition of the phrase under applicable law. Accordingly, in certain circumstances, there may be a degree of uncertainty as to whether a particular transaction would involve the property or assets of a person “substantially as an entirety.”

The Subordinated Indenture provides that when, among other things, all subordinated notes not previously delivered to the trustee for cancellation:

and we irrevocably deposit or cause to be deposited with the trustee as trust funds in trust for such purpose money, in an amount sufficient to pay and discharge the entire indebtedness on the subordinated notes not previously delivered to the trustee for cancellation, for the principal and any premium and interest to the date of such deposit (in the case of subordinated notes which have become due and payable) or to the Maturity Date or the date of redemption, as the case may be;

then, upon our request, the Subordinated Indenture will cease to be of further effect, and we will be deemed to have satisfied and discharged the Subordinated Indenture with respect to the subordinated notes.

Our obligations will be deemed to have been paid and discharged if the following applicable conditions have been satisfied:

Any defeasance of the subordinated notes pursuant to the Subordinated Indenture will be subject to our obtaining the prior approval of the Federal Reserve and any additional requirements that the Federal Reserve may impose with respect to defeasance of the subordinated notes. Notwithstanding the foregoing, if, due to a change in law, regulation

or policy subsequent to the issue date of the subordinated notes the Federal Reserve does not require that defeasance of instruments be subject to Federal Reserve approval in order for the instrument to be accorded Tier 2 capital treatment, then no such approval of the Federal Reserve will be required for such defeasance.

Benchmark Replacement. If the calculation agent determines that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred on or prior to the Reference Time in respect of any determination of the Benchmark on any date, then the Benchmark Replacement will replace the then-current Benchmark for all purposes relating to the subordinated notes during the floating rate period in respect of such determination on such date and all determinations on all subsequent dates.

Benchmark Replacement Conforming Changes. In connection with the implementation of a Benchmark Replacement, the calculation agent will have the right to make Benchmark Replacement Conforming Changes from time to time.

Certain Defined Terms. As used herein:

“Benchmark Replacement” means the Interpolated Benchmark with respect to the then-current Benchmark, plus the Benchmark Replacement Adjustment for such Benchmark; provided that if (a) the calculation agent cannot determine the Interpolated Benchmark as of the Benchmark Replacement Date or (b) the then-current Benchmark is Three-Month Term SOFR and a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to Three-Month Term SOFR (in which event no Interpolated Benchmark with respect to Three-Month Term SOFR shall be determined), then

“Benchmark Replacement” means the first alternative set forth in the order below that can be determined by the calculation agent as of the Benchmark Replacement Date:

“Benchmark Replacement Adjustment” means the first alternative set forth in the order below that can be determined by the calculation agent as of the Benchmark Replacement Date:

“Benchmark Replacement Conforming Changes” means, with respect to any Benchmark Replacement, any technical, administrative or operational changes (including changes to the definition of “interest period,” timing and frequency of determining rates with respect to each interest period and making payments of interest, rounding of amounts or tenors, and other administrative matters) that the calculation agent decides may be appropriate to reflect the adoption of such Benchmark Replacement in a manner substantially consistent with market practice (or, if the

calculation agent decides that adoption of any portion of such market practice is not administratively feasible or if the calculation agent determines that no market practice for use of the Benchmark Replacement exists, in such other manner as the calculation agent determines is reasonably necessary).

“Benchmark Replacement Date” means the earliest to occur of the following events with respect to the then-current Benchmark:

For the avoidance of doubt, for purposes of the definitions of Benchmark Replacement Date and Benchmark Transition Event, references to the Benchmark also include any reference rate underlying the Benchmark (for example, if the Benchmark becomes Compounded SOFR, references to the Benchmark would include SOFR).

For the avoidance of doubt, if the event giving rise to the Benchmark Replacement Date occurs on the same day as, but earlier than, the Reference Time in respect of any determination, the Benchmark Replacement Date will be deemed to have occurred prior to the Reference Time for such determination.

“Benchmark Transition Event” means the occurrence of one or more of the following events with respect to the then-current Benchmark:

“Compounded SOFR” means the compounded average of SOFRs for the applicable Corresponding Tenor, with the rate, or methodology for this rate, and conventions for this rate being established by the calculation agent in accordance with:

For the avoidance of doubt, the calculation of Compounded SOFR shall exclude the Benchmark Replacement Adjustment (if applicable) and the spread of 485 basis points per annum.

“Corresponding Tenor” with respect to a Benchmark Replacement means a tenor (including overnight) having approximately the same length (disregarding business day adjustment) as the applicable tenor for the then-current Benchmark.

“Interpolated Benchmark” with respect to the Benchmark means the rate determined for the Corresponding Tenor by interpolating on a linear basis between: (1) the Benchmark for the longest period (for which the Benchmark is available) that is shorter than the Corresponding Tenor, and (2) the Benchmark for the shortest period (for which the Benchmark is available) that is longer than the Corresponding Tenor.

“ISDA Definitions” means the 2006 ISDA Definitions published by the International Swaps and Derivatives Association, Inc. or any successor thereto, as amended or supplemented from time to time, or any successor definitional booklet for interest rate derivatives published from time to time.

“ISDA Fallback Adjustment” means the spread adjustment (which may be a positive or negative value or zero) that would apply for derivatives transactions referencing the ISDA Definitions to be determined upon the occurrence of an index cessation event with respect to the Benchmark for the applicable tenor.

“ISDA Fallback Rate” means the rate that would apply for derivatives transactions referencing the ISDA Definitions to be effective upon the occurrence of an index cessation date with respect to the Benchmark for the applicable tenor excluding the applicable ISDA Fallback Adjustment.

“Unadjusted Benchmark Replacement” means the Benchmark Replacement excluding the Benchmark Replacement Adjustment.

The terms “Federal Reserve Bank of New York’s Website,” “Reference Time,” “Relevant Governmental Body,” “SOFR” and “Term SOFR” have the meanings set forth above under the heading “—Interest.”

The calculation agent is expressly authorized to make certain determinations, decisions and elections under the terms of the subordinated notes, including with respect to the use of Three-Month Term SOFR as the Benchmark for the floating rate period and under the benchmark transition provisions. Any determination, decision or election that may be made by the calculation agent under the terms of the subordinated notes, including any determination with respect to a tenor, rate or adjustment or of the occurrence or non-occurrence of an event, circumstance or date and any decision to take or refrain from taking any action or any selection:

The subordinated notes offered hereby will be issued only in fully registered form, without interest coupons, and in minimum denominations of $1,000 and integral multiples of $1,000 in excess thereof.

The subordinated notes offered hereby will be evidenced by a global note which will be deposited with, or on behalf of, DTC, or any successor thereto, and registered in the name of Cede & Co., or Cede, as nominee of DTC. Except as set forth below, record ownership of the global note may be transferred, in whole or in part, only to another nominee of DTC or to a successor of DTC or its nominee.

The global note will not be registered in the name of any person, or exchanged for subordinated notes that are registered in the name of any person, other than DTC or its nominee, unless one of the following occurs:

In those circumstances, DTC will determine in whose names any securities issued in exchange for the global note will be registered. Any such subordinated notes in certificated form will be issued in minimum denominations of $1,000 and multiples of $1,000 in excess thereof and may be transferred or exchanged only in such minimum denominations. In connection with any proposed exchange of a global note for a certificated note, there shall be provided to the trustee all information necessary to allow the trustee to comply with any applicable tax reporting obligations, including without limitation any cost basis reporting obligations under Internal Revenue Code Section 6045. The trustee may rely on information provided to it and shall have no responsibility to verify or ensure the accuracy of such information.

DTC or its nominee will be considered the sole owner and holder of the global note for all purposes, and as a result:

The laws of some jurisdictions require that certain kinds of purchasers (for example, certain insurance companies) can only own securities in definitive (certificated) form. These laws may limit your ability to transfer your beneficial interests in the global note to these types of purchasers.

Only institutions (such as a securities broker or dealer) that have accounts with DTC or its nominee (called “participants”) and persons that may hold beneficial interests through participants (including through Euroclear Bank SA/NV or Clearstream Banking, société anonyme, as DTC participants) can own a beneficial interest in the global note. The only place where the ownership of beneficial interests in the global note will appear and the only way the transfer of those interests can be made will be on the records kept by DTC (for their participants’ interests) and the records kept by those participants (for interests of persons held by participants on their behalf).

Secondary trading in bonds and notes of corporate issuers is generally settled in clearing-house (that is, next-day) funds. In contrast, beneficial interests in a global note usually trade in DTC’s same-day funds settlement system, and settle in immediately available funds. We make no representations as to the effect that settlement in immediately available funds will have on trading activity in those beneficial interests.

We will make cash payments of interest on and principal of the global note to Cede, the nominee for DTC, as the registered owner of the global note. We will make these payments by wire transfer of immediately available funds on each payment date.

You may exchange or transfer the subordinated notes at the corporate trust office of the trustee under the Subordinated Indenture for the series of subordinated notes or at any other office or agency maintained by us for those purposes. We will not require payment of a service charge for any transfer or exchange of the subordinated notes, but NBT Bancorp may require payment of a sum sufficient to cover any applicable tax or other governmental charge. The transferor of any note shall provide or cause to be provided to the trustee all information necessary to allow the trustee to comply with any applicable tax reporting obligations, including without limitation any cost basis reporting obligations under Internal Revenue Code Section 6045. The trustee may rely on information provided to it and shall have no responsibility to verify or ensure the accuracy of such information.

We have been informed that, with respect to any cash payment of interest on or principal of the global note, DTC’s practice is to credit participants’ accounts on the payment date with payments in amounts proportionate to

their respective beneficial interests in the subordinated notes represented by the global note as shown on DTC’s records, unless DTC has reason to believe that it will not receive payment on that payment date. Payments by participants to owners of beneficial interests in subordinated notes represented by the global note held through participants will be the responsibility of those participants, as is now the case with securities held for the accounts of customers registered in “street name.”

We also understand that neither DTC nor Cede will consent or vote with respect to the subordinated notes. We have been advised that under its usual procedures, DTC will mail or send an “omnibus proxy” to us as soon as possible after the record date. The omnibus proxy assigns Cede’s consenting or voting rights to those participants to whose accounts the subordinated notes are credited on the record date identified in a listing attached to the omnibus proxy.

Because DTC can only act on behalf of participants, who in turn act on behalf of indirect participants, the ability of a person having a beneficial interest in the principal amount represented by the global note to pledge the interest to persons or entities that do not participate in the DTC book-entry system, or otherwise take actions in respect of that interest, may be affected by the lack of a physical certificate evidencing its interest.

DTC has advised us that it will take any action permitted to be taken by a holder of notes (including the presentation of notes for exchange) only at the direction of one or more participants to whose account with DTC interests in the global note are credited and only in respect of such portion of the principal amount of the subordinated notes represented by the global note as to which such participant has, or participants have, given such direction.

DTC has also advised us as follows: DTC is a limited purpose trust company organized under the laws of the State of New York, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the Uniform Commercial Code, as amended, and a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act. DTC was created to hold securities for its participants and facilitate the clearance and settlement of securities transactions between participants through electronic book-entry changes in accounts of its participants.

Participants include securities brokers and dealers, banks, trust companies and clearing corporations and may include certain other organizations. Certain of such participants (or their representatives), together with other entities, own DTC. Indirect access to the DTC system is available to other entities such as banks, brokers, dealers and trust companies that clear through or maintain a custodial relationship with a participant, either directly or indirectly. The rules applicable to DTC and its direct and indirect participants are on file with the SEC.

The policies and procedures of DTC, which may change periodically, will apply to payments, transfers, exchanges and other matters relating to beneficial interests in the global note. We and the trustee have no responsibility or liability for any aspect of DTC’s or any participants’ records relating to beneficial interests in the global note, including for payments made on the global note, and we and the trustee are not responsible for maintaining, supervising or reviewing any of those records.

We will appoint a calculation agent for the subordinated notes prior to the commencement of the floating rate period and will keep a record of such appointment at our principal offices, which will be available to any holder of the subordinated notes upon request. In addition, we or an affiliate of ours may assume the duties of the calculation agent. We will act as the initial calculation agent. The trustee will have no responsibility for any act or omission of the calculation agent.

The trustee under the Subordinated Indenture is U.S. Bank National Association. If an event of default with respect to the subordinated notes occurs, and is not cured, the trustee will be required to use the degree of care of a prudent person in the conduct of his or her own affairs in the exercise of its powers. Subject to the provisions of the Subordinated Indenture, the trustee will be under no obligation to exercise any of its rights or powers under the Subordinated Indenture at the request of any holders of the subordinated notes, unless they have offered to the trustee security or indemnity satisfactory to the trustee.

U.S. Bank National Association, in the future, may be the trustee under other indentures pursuant to which we issue debt. Pursuant to the Trust Indenture Act, if a default occurs with respect to the securities of any series, the

trustee will be required to eliminate any conflicting interest as defined in the Trust Indenture Act or resign as trustee with respect to the securities of that series within 90 days of such default, unless such default were cured, duly waived or otherwise eliminated. In the event of such resignation, we would be required to appoint a successor trustee under the Subordinated Indenture for the subordinated notes.

From time to time, we and our subsidiaries may maintain deposit accounts and conduct other banking transactions, including lending transactions, with the trustee in the ordinary course of business. We also maintain banking relationships with U.S. Bank National Association and its affiliates in the ordinary course of business. These banking relationships include U.S. Bank National Association providing us with general banking services. The trustee assumes no responsibility for the accuracy or completeness of the information concerning us or our affiliates or any other party contained in this document or the related documents or for any failure by us or any other party to disclose events that may have occurred and may affect the significance or accuracy of such information.

We will pay principal and interest on the subordinated notes at the corporate trust office of the trustee or at such other place that we appoint in accordance with the Subordinated Indenture.

We will pay any interest on the subordinated notes to the registered owner of the subordinated notes at the close of business on the record date for the interest, except in the case of defaulted interest.

Any moneys deposited with the trustee or any paying agent, or then held by us in trust, for the payment of the principal of and interest on any subordinated note that remains unclaimed for two years after the principal or interest has become due and payable will, at our request, be repaid to us, or (if then held by us) be discharged from such trust. After repayment to us, you are entitled to seek payment only from us as an unsecured general creditor.

The Subordinated Indenture and the subordinated notes are governed by and construed in accordance with the laws of the State of New York. The Subordinated Indenture provides that we and the trustee, and each holder of a subordinated note by its acceptance thereof, irrevocably waives, to the fullest extent permitted by applicable law, any and all right to trial by jury in any legal proceeding arising out of or relating to the Subordinated Indenture or the subordinated notes, or any transaction contemplated thereby.

The following is a summary of certain U.S. federal income tax consequences of the acquisition, ownership and disposition of the subordinated notes described in this prospectus supplement. This summary is based upon the provisions of the Internal Revenue Code of 1986, as amended (the “Code”), applicable U.S. Treasury Regulations promulgated thereunder, judicial authorities and administrative interpretations, in each case as of the date of this prospectus supplement, all of which are subject to change or different interpretations, possibly with retroactive effect. We cannot assure you that the U.S. Internal Revenue Service (the “IRS”) will not challenge one or more of the tax consequences described in this discussion, and we have not obtained, nor do we intend to obtain, a ruling from the IRS or an opinion of counsel with respect to the U.S. federal income tax consequences of acquiring, owning or disposing of the subordinated notes.

This discussion does not purport to address all U.S. federal income tax consequences that may be relevant to a holder in light of the holder’s particular circumstances or status, nor does it discuss the U.S. federal income tax consequences to certain types of holders subject to special treatment under the U.S. federal income tax laws, such as banks and other financial institutions, insurance companies, regulated investment companies, tax-exempt entities, dealers in securities or foreign currency, real estate investment trusts, thrifts, traders in securities that have elected the mark-to-market method of accounting for their securities, partnerships or other pass-through entities (or investors in such entities), U.S. Holders (as defined below) whose “functional currency” is not the U.S. dollar, U.S. Holders that hold subordinated notes through non-U.S. brokers or other non-U.S. intermediaries, persons required to accelerate the recognition of any item of income as a result of such income being included on an applicable financial statement, U.S. expatriates and former long-term residents of the United States or persons that hold the subordinated notes as part of a hedge, wash sale, conversion transaction, straddle or other risk reduction transaction. This discussion is limited to those holders that purchase notes for cash in this offering at their “issue price” (which is the first price at which a substantial amount of the subordinated notes is sold for cash to investors other than to bond houses, brokers or similar persons or organizations acting in the capacity of underwriters, placement agents or wholesalers) and that hold the subordinated notes as capital assets (generally, property held for investment). Moreover, this discussion does not address the effect of any alternative minimum tax, the Medicare tax on investment income, state, local or non-U.S. tax laws or the application of any U.S. federal taxes other than U.S. federal income taxes (such as U.S. federal estate or gift taxes).

If any entity or arrangement that is treated as a partnership for U.S. federal income tax purposes is a holder of subordinated notes, the U.S. federal income tax treatment of a partner in the partnership generally will depend upon the status of the partner and the activities of the partnership. If you are a partnership or a partner in a partnership considering an investment in the subordinated notes, you should consult your own tax advisor about the tax consequences of acquiring, owning and disposing of the subordinated notes.

Investors considering the purchase of subordinated notes should consult their own tax advisors regarding the application of the U.S. federal tax laws to their particular situations and the applicability and effect of state, local or non-U.S. tax laws and tax treaties.

You are a U.S. Holder for purposes of this discussion if you are a beneficial owner of a subordinated note and, for U.S. federal income tax purposes, you are:

Under applicable Treasury Regulations, a debt instrument will qualify as a “variable rate debt instrument” if (i) its issue price does not exceed the total noncontingent principal payments due under the debt instrument by more than a specified de minimis amount and (ii) the debt instrument provides for stated interest, paid or compounded at least annually, at current values of a single fixed rate and one or more qualified floating rates. We expect that the subordinated notes will meet the requirements for being variable rate debt instruments, and accordingly we intend to treat the subordinated notes as variable rate debt instruments for U.S. federal income tax purposes. Under this characterization, payments treated as qualified stated interest (“QSI”) on the subordinated notes generally will be taxable to you as ordinary income at the time such QSI is received or accrued in accordance with your regular method of accounting for U.S. federal income tax purposes. QSI generally means stated interest that is unconditionally payable in cash at least annually at a single fixed rate, but as discussed below, special rules are applicable to variable rate debt instruments.

The subordinated notes will be treated as issued with OID for U.S. federal income tax purposes if the issue price of the subordinated notes is less than the stated redemption price at maturity by more than a de minimis amount. The stated redemption price at maturity for the subordinated notes is the sum of (i) the principal amount of the subordinated notes and (ii) any interest on the subordinated notes that is not QSI. The issue price of debt instruments equals the first price at which a substantial amount of the debt instruments has been sold (ignoring sales to bond houses, brokers or similar persons or organizations acting in the capacity of underwriters, placement agents or wholesalers). As discussed below, solely for purposes of calculating OID, special rules apply for determining the “maturity” of a subordinated note. If the subordinated notes are issued with OID, a U.S. Holder generally must include such OID in taxable income (as ordinary income) as such OID accrues in accordance with a constant yield method based on a compounding of interest, regardless of the U.S. Holder’s regular method of accounting for U.S. federal income tax purposes. Thus, a U.S. Holder generally will be required to include OID in income in advance of the receipt of the cash to which such OID is attributable.

Under applicable Treasury Regulations, to determine the amount of QSI and OID in respect of a variable rate debt instrument, an “equivalent fixed rate debt instrument” must be constructed. The equivalent fixed rate debt instrument of a variable rate debt instrument that has an initial fixed rate followed by one or more qualified floating rates, such as a subordinated note, is constructed as follows: (i) first, the initial fixed rate is replaced with a qualified floating rate such that the fair market value of a subordinated note as of the subordinated note’s issue date would be approximately the same as the fair market value of an otherwise identical debt instrument that provides for the replacement qualified floating rate rather than the fixed rate, and (ii) second, each floating rate (including the floating rate determined under clause (i) of this paragraph) is converted into a fixed rate substitute (which, in each case, generally will be the value of each floating rate as of the issue date of the subordinated notes). When the equivalent fixed rate debt instrument has been constructed pursuant to the foregoing rules, the amount of QSI and OID, if any, are determined for the equivalent fixed rate debt instrument by applying the general OID rules to the equivalent fixed rate debt instrument, and a U.S. Holder of subordinated notes will account for such OID, if any, and QSI as if the U.S. Holder held the equivalent fixed rate debt instrument. For each accrual period, appropriate adjustments will be made to the amount of QSI or OID assumed to have been accrued or paid with respect to the equivalent fixed rate debt instrument in the event that such amounts differ from the actual amount of interest accrued or paid on the subordinated notes during the accrual period.

The Treasury Regulations provide special rules for determining the yield and maturity of a debt instrument, such as the subordinated notes, that provide an issuer with the option to redeem the instrument at specified times. The Treasury Regulations generally deem an issuer to exercise a redemption option in a manner that minimizes the yield on the debt instrument for purposes of determining whether a debt instrument is issued with OID. Under the terms of the subordinated notes, if the initial fixed rate substitute on the equivalent fixed rate debt instrument (as determined in the manner described above) is greater than the fixed rate substitute of the floating rate (as determined in the manner described above), the Notes will be presumed not to be redeemed and original issue discount with respect to the Notes will be calculated as described above. If, however, the initial fixed rate substitute on the equivalent fixed rate debt instrument (as determined in the manner described above) is less than the fixed rate substitute of the floating rate (as determined in the manner described above), the yield on the subordinated notes will be minimized if the subordinated notes are redeemed immediately before the change in the interest rate on July 1, 2025, and, therefore, the subordinated notes will be treated as maturing on such date for OID purposes. This assumption is made solely for purposes of determining whether the subordinated notes are issued with OID for U.S. federal income tax purposes and is not an indication of our intention to redeem or not to redeem the subordinated notes at any time. If, contrary

to this presumption, the subordinated notes are not redeemed prior to the change in the interest rate on July 1, 2025, then, solely for OID purposes, the subordinated notes will be deemed to be reissued at their adjusted issue price on the date that they are not redeemed. This deemed reissuance should not result in taxable gain or loss to U.S. Holders.

Based on current market conditions and the manner in which the interest rates on the Notes are determined, we expect that when the foregoing calculations are completed, the Notes will be presumed to remain outstanding until maturity and have no original issue discount or will have de minimis original issue discount that can be disregarded and that, therefore, all interest payable on the Notes will be treated as qualified stated interest.

You generally will recognize capital gain or loss on a sale, redemption, exchange, retirement or other taxable disposition of a subordinated note equal to the difference, if any, between (i) the amount realized on such disposition (excluding amounts attributable to any accrued but unpaid stated interest, which will be taxable as ordinary income to the extent you have not previously included such amounts in income) and (ii) your adjusted tax basis in the subordinated note. The amount realized will equal the sum of any cash and the fair market value of any other property received on the disposition. Your adjusted tax basis in a subordinated note generally will equal the amount you paid for the subordinated note, increased by any OID previously included in your gross income with respect to the subordinated note (including OID accrued in the year of the sale or other disposition) less any payment (other than QSI) made on the Note. Any such gain or loss will be long-term capital gain or loss if you held the subordinated note for more than one year at the time of the disposition. Long-term capital gains of non-corporate U.S. Holders generally are eligible for reduced rates of taxation. The deductibility of capital losses is subject to limitations.

Payments of stated interest which is QSI, accruals of OID and the proceeds of a disposition (including a retirement or redemption) of subordinated notes may be reported to the IRS. These information reporting requirements, however, do not apply with respect to certain exempt U.S. Holders, such as corporations.

Backup withholding (currently at a rate of 24%) may apply to payments of the foregoing amounts, unless you provide the applicable withholding agent with your taxpayer identification number, certified under penalties of perjury, as well as certain other information, or otherwise establish an exemption from backup withholding.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules will be allowed as a credit against your U.S. federal income tax liability, if any, and may entitle you to a refund, provided the required information is timely furnished to the IRS.

You are a “Non-U.S. Holder” for purposes of this discussion if you are a beneficial owner of a subordinated note and you are, for U.S. federal income tax purposes, an individual, corporation, estate or trust that is not a U.S. Holder.

Subject to the discussion below under the headings “—Information Reporting and Backup Withholding” and “Foreign Account Tax Compliance Act,” payments of interest (which, for purposes of this discussion of Non-U.S. Holders, shall include any OID) on the subordinated notes generally will be exempt from U.S. federal income and withholding tax under the “portfolio interest” exemption if you properly certify as to your non-U.S. status, as described below, and:

The portfolio interest exemption applies only if you appropriately certify as to your non-U.S. status. You generally can meet this certification requirement by providing a properly executed IRS Form W-8BEN or W-8BEN-E, as applicable (or appropriate substitute or successor form) to the applicable withholding agent. If you hold the subordinated notes through a financial institution or other agent acting on your behalf, you may be required to provide appropriate certifications to your agent. Your agent then generally will be required to provide appropriate certifications to the applicable withholding agent, either directly or through other intermediaries.

If you cannot satisfy the requirements described above, payments of interest made to you will be subject to U.S. federal withholding tax, currently at a 30% rate, unless (i) you provide the applicable withholding agent with a properly executed IRS Form W-8BEN or W-8BEN-E, as applicable (or appropriate substitute or successor form) claiming an exemption from (or a reduction of) withholding under an applicable income tax treaty or (ii) the payments of interest are effectively connected with your conduct of a trade or business in the United States (and, in the event that an income tax treaty is applicable, payments of interest are also attributable to a U.S. permanent establishment or fixed base maintained by you in the United States, as applicable) and you meet the certification requirements described below (see “—Income or Gain Effectively Connected with a U.S. Trade or Business”).

Subject to the discussion below under the headings “—Information Reporting and Backup Withholding” and “Foreign Account Tax Compliance Act,” you generally will not be subject to U.S. federal income or withholding tax on any gain realized on a sale, redemption, exchange, retirement or other taxable disposition of a subordinated note (other than amounts attributable to accrued and unpaid interest, which will be treated as described above under “—Interest on the Subordinated Notes”) unless:

If you are a Non-U.S. Holder described in the first bullet point above, you generally will be subject to U.S. federal income tax as described below (see “—Income or Gain Effectively Connected with a U.S. Trade or Business”). If you are a Non-U.S. Holder described in the second bullet point above, you generally will be subject to U.S. federal income tax at a flat 30% rate (or a lower applicable income tax treaty rate) on the gain derived from the sale, redemption, exchange, retirement or other taxable disposition, which may be offset by certain U.S.-source capital losses, unless an applicable income tax treaty provides otherwise.

If any interest on the subordinated notes or gain from a sale, redemption, exchange, retirement or other taxable disposition of the subordinated notes is effectively connected with a U.S. trade or business conducted by you, then you generally will be subject to U.S. federal income tax on such interest or gain on a net income basis in the same manner as a U.S. Holder (unless an applicable income tax treaty provides otherwise). If interest received with respect to the subordinated notes is effectively connected income, the U.S. federal withholding tax described above will not apply (assuming an appropriate certification is provided) unless an applicable income tax treaty provides otherwise. You generally can meet the certification requirements by providing a properly executed IRS Form W-8ECI (or other applicable form) to the applicable withholding agent. If you are eligible for the benefits of an income tax treaty between the United States and your country of residence, any effectively connected income or gain generally will be subject to U.S. federal income tax only if it is also attributable to a permanent establishment or fixed base maintained by you in the United States. In addition, if you are a corporation for U.S. federal income tax purposes, that portion of your earnings and profits that is attributable to such effectively connected income or gain, subject to certain adjustments, may be subject to a “branch profits tax” at a 30% rate (or a lower applicable income tax treaty rate).

Payments to you of interest on a subordinated note, and amounts withheld from such payments, if any, generally will be required to be reported to the IRS and may also be made available to the tax authorities of the country in which you are a tax resident under the provisions of an applicable income tax treaty or agreement. Backup withholding (currently at a rate of 24%) generally will not apply to payments of interest on a subordinated note to a Non-U.S. Holder if the certification described in “—Interest on the Subordinated Notes” above is provided by the Non-U.S. Holder, or the Non-U.S. Holder otherwise establishes an exemption.

Proceeds from a disposition (including a retirement or redemption) of a subordinated note effected by the U.S. office of a U.S. or non-U.S. broker will be subject to information reporting requirements and backup withholding unless you properly certify, under penalties of perjury, as to your non-U.S. status and certain other conditions are met, or you otherwise establish an exemption. Information reporting and backup withholding generally will not apply to any proceeds from a disposition of a subordinated note effected outside the United States by a non-U.S. office of a broker, unless such broker has certain connections to the United States, in which case information reporting, but not backup withholding, will apply unless the broker has documentary evidence in its records that you are a Non-U.S. Holder and certain other conditions are met, or you otherwise establish an exemption.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules will be allowed as a credit against your U.S. federal income tax liability, if any, and may entitle you to a refund, provided the required information is timely furnished to the IRS.

The Foreign Account Tax Compliance Act imposes a U.S. federal withholding tax (separate and apart from, but without duplication of, the withholding tax described above) at a rate of 30% on payments of interest on, and, subject to the proposed U.S. Treasury Regulations discussed below, the gross proceeds from a disposition (including a retirement or redemption) of, a debt instrument paid to certain non-U.S. entities, including certain foreign financial institutions and investment funds (including, in some instances, where such an entity is acting as an intermediary), unless such non-U.S. entity complies with certain withholding and reporting requirements regarding U.S. account holders and U.S. owners of such entity’s equity and debt. Pursuant to proposed U.S. Treasury Regulations (upon which taxpayers are permitted to rely until final U.S. Treasury Regulations are issued), this withholding tax generally will not apply to payments of gross disposition proceeds. Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States with respect to these rules may be subject to different rules. Under certain circumstances, a beneficial owner of subordinated notes may be eligible for a refund or credit of such taxes. Prospective purchasers of the subordinated notes should consult their own tax advisors regarding these withholding and reporting provisions.

The preceding discussion of certain U.S. federal income tax consequences is for general information only and is not tax advice. Each prospective investor should consult its own tax advisor regarding the particular U.S. federal, state, local and non-U.S. tax consequences of acquiring, owning and disposing of the subordinated notes, including the consequences of any proposed change in applicable laws.

A fiduciary of a pension, profit-sharing or other employee benefit plan subject to the U.S. Employee Retirement Income Security Act of 1974, as amended (“ERISA”) (each, an “ERISA Plan”), should consider the fiduciary standards of ERISA in the context of the ERISA Plan’s particular circumstances before authorizing an investment in the subordinated notes. Among other factors, the fiduciary should consider whether the investment would satisfy the prudence and diversification requirements of ERISA and would be consistent with the documents and instruments governing the ERISA Plan, and whether the investment would involve a non-exempt prohibited transaction under ERISA or the Code.

Section 406 of ERISA and Section 4975 of the Code prohibit ERISA Plans, as well as individual retirement accounts, and any other plans that are subject to Section 4975 of the Code (together with ERISA Plans, “Plans”) from engaging in certain transactions involving “plan assets” with persons who are “parties in interest” under ERISA or “disqualified persons” under the Code with respect to the Plan unless an exemption is available. A violation of these prohibited transaction rules may result in excise tax or other liabilities under ERISA or the Code for those persons, unless exemptive relief is available under an applicable statutory, regulatory or administrative exemption. Employee benefit plans that are governmental plans (as defined in Section 3(32) of ERISA), certain church plans (as defined in Section 3(33) of ERISA that have not made an election under Section 410(d) of the Code) and non-U.S. plans (as described in Section 4(b)(4) of ERISA) (“Non-ERISA Arrangements”) are not subject to the requirements of Section 406 of ERISA or Section 4975 of the Code but may be subject to similar provisions under applicable federal, state, local, non-U.S. or other laws (“Similar Laws”).

The acquisition and holding of the subordinated notes or any interest therein by a Plan or any entity whose underlying assets include “plan assets” by reason of any Plan’s investment in the entity (a “Plan Asset Entity”) with respect to which we or any paying agent or any of our or its respective affiliates is or becomes a party in interest or disqualified person may result in a prohibited transaction under Section 406 of ERISA or Section 4975 of the Code, unless the subordinated notes are acquired and held pursuant to an applicable exemption. The U.S. Department of Labor has issued prohibited transaction class exemptions, or “PTCEs,” that may provide exemptive relief if required for direct or indirect prohibited transactions that may arise from the purchase, holding or disposition of the subordinated notes, or any interest therein. These exemptions include PTCE 84-14 (for certain transactions determined by independent qualified professional asset managers), PTCE 90-1 (for certain transactions involving insurance company pooled separate accounts), PTCE 91-38 (for certain transactions involving bank collective investment funds), PTCE 95-60 (for transactions involving certain insurance company general accounts), and PTCE 96-23 (for transactions managed by in-house asset managers). In addition, section 408(b)(17) of ERISA and Section 4975(d)(20) of the Code (the “service provider exemption”) may provide an exemption for the purchase and sale of the subordinated notes, provided that (i) the issuer of the subordinated notes is not a party in interest or disqualified person with respect to an investing Plan other than by reason of providing services to the Plan or a relationship to a service provider, (ii) and neither the issuer of the subordinated notes nor any of its affiliates has or exercises any discretionary authority or control or renders any investment advice with respect to the assets of the Plan involved in the transaction, and provided further that the Plan pays no more and receives no less than “adequate consideration” in connection with the transaction. There can be no assurance that all of the conditions of any such exemptions will be satisfied.

Any purchaser or holder of the subordinated notes or any interest therein will be deemed to have represented by its purchase and holding of the subordinated notes or any interest therein that it either (1) is not a Plan, a Plan Asset Entity or a Non-ERISA Arrangement and is not purchasing or holding the subordinated notes or any interest therein on behalf of or with the assets of any Plan, a Plan Asset Entity or Non-ERISA Arrangement or (2) the purchase, holding and disposition of the subordinated notes, or any interest in the subordinated notes, will not constitute or result in a non-exempt prohibited transaction under ERISA or the Code or a similar violation under any applicable Similar Laws.

Due to the complexity of these rules and the penalties that may be imposed upon persons involved in non-exempt prohibited transactions, it is important that fiduciaries or other persons considering purchasing the subordinated notes or any interest therein on behalf of or with the assets of any Plan, a Plan Asset Entity or Non-ERISA Arrangement consult with their legal counsel regarding the potential consequences under ERISA and Section 4975 of the Code, and, if applicable, the availability of exemptive relief under any of the PTCEs listed above, the service provider exemption or the potential consequences of any purchase or holding under Similar Laws, as applicable. Purchasers of the subordinated notes have exclusive responsibility for ensuring that their purchase,

holding and disposition of the subordinated notes or any interest therein do not violate the fiduciary or prohibited transaction rules of ERISA or the Code or any similar provisions of Similar Laws. The sale of any subordinated notes to a Plan, Plan Asset Entity or Non-ERISA Arrangement is in no respect a recommendation to make such a purchase or a representation by us or any of our affiliates or representatives that such an investment meets all relevant legal requirements with respect to investments by any such Plans, Plan Asset Entities or Non-ERISA Arrangements generally or any particular Plan, Plan Asset Entity or Non-ERISA Arrangement or that such investment is appropriate for such Plans, Plan Asset Entities or Non-ERISA Arrangements generally or any particular Plan, Plan Asset Entity or Non-ERISA Arrangement.

The foregoing discussion is merely a summary and should not be construed as legal advice or as complete in all relevant respects.

We have entered into an underwriting agreement, dated June 16, 2020 (the “Underwriting Agreement”), with Keefe, Bruyette & Woods, Inc. and Piper Sandler & Co., or the underwriters, with respect to the subordinated notes. Subject to certain conditions, the underwriters have agreed to purchase, severally, the aggregate principal amount of subordinated notes set forth next to their names in the following table.

The Underwriting Agreement provides that the obligations of the underwriters to purchase the subordinated notes offered hereby are subject to certain conditions precedent and that the underwriters will purchase all of the subordinated notes if any of the subordinated notes are purchased.

The subordinated notes sold by the underwriters to the public will be offered at the public offering price set forth on the cover of this prospectus supplement. The underwriters may offer the subordinated notes to selected dealers at the public offering price set forth on the cover of this prospectus supplement less a concession not in excess of 0.50% of the principal amount per note. After the initial offering, the underwriters may change the offering price and the other selling terms. The offering of the subordinated notes by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part.

The following table shows the public offering price, the underwriting discounts and commissions that we are to pay the underwriters and the proceeds, before expenses, to us in connection with this offering (expressed as a percentage of the principal amount of the subordinated notes offered hereby).

We estimate that our total expenses for this offering, not including underwriting discounts and commissions, will be approximately $611,682. We also have agreed to reimburse the underwriters for certain of their fees and expenses related to the offering. In accordance with FINRA Rule 5110, the underwriters’ reimbursed expenses are deemed underwriting compensation for this offering.

We have agreed to indemnify the underwriters, and persons who control the underwriters, against certain liabilities, including liabilities under the Securities Act and to contribute to payments that the underwriters may be required to make in respect of these liabilities.

There is currently no public trading market for the subordinated notes. In addition, we have not applied and do not intend to apply to list the subordinated notes on any national securities exchange or to have the subordinated notes quoted on an automated dealer quotation system. The underwriters have advised us that they intend to make a market in the subordinated notes. However, the underwriters are not obligated to do so and may discontinue any

market-making in the subordinated notes at any time in their sole discretion and without prior notice. Therefore, we cannot assure you that a liquid trading market for the subordinated notes will develop or continue, that you will be able to sell your subordinated notes at a particular time, or that the price that you receive when you sell will be favorable.

We have agreed with the underwriters that for a period of 45 days from the date of the Underwriting Agreement, we and our subsidiaries will not, without the prior consent of the underwriters, offer or sell, or enter into any agreement to sell, any debt securities (excluding deposit obligations) of ours or of our subsidiaries.

In connection with this offering of the subordinated notes, the underwriters may engage in overallotment, stabilizing transactions and syndicate covering transactions. Overallotment involves sales in excess of the offering size, which create a short position for the underwriters. Stabilizing transactions involve bids to purchase the subordinated notes in the open market for the purpose of pegging, fixing or maintaining the price of the subordinated notes. Syndicate covering transactions involve purchases of the subordinated notes in the open market after the distribution has been completed in order to cover short positions. Stabilizing transactions and syndicate covering transactions may cause the price of the subordinated notes to be higher than it would otherwise be in the absence of those transactions. If the underwriters engage in stabilizing or syndicate covering transactions, they may discontinue such activities at any time without notice.

Neither we nor the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of the subordinated notes. In addition, neither we nor any of the underwriters make any representation that the underwriters will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

This prospectus supplement and the accompanying prospectus may be made available in electronic format on websites or through other online services maintained by the underwriters or their respective affiliates.

Other than the prospectus supplement and the accompanying prospectus in electronic format, information on such websites and any information contained in any other website maintained by any of the underwriters or its respective affiliates is not part of this prospectus supplement or our registration statement of which the related prospectus forms a part, has not been approved or endorsed by us or the underwriters in their capacity as underwriters and should not be relied on by investors.

The underwriters and their affiliates have engaged, or may in the future engage, in investment banking transactions and other commercial dealings in the ordinary course of business with us or our affiliates. The underwriters have received, or may in the future receive, customary fees and commissions for these transactions.

In addition, in the ordinary course of its business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade indebtedness and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own accounts and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Other than in the United States, no action has been taken by us or the underwriters that would permit a public offering of the subordinated notes offered by this prospectus supplement in any jurisdiction in which action for that purpose is required. The subordinated notes offered by this prospectus supplement may not be offered or sold, directly or indirectly, nor may this prospectus supplement, the accompanying prospectus or any other offering material or advertisements in connection with the offer and sale of any such securities be distributed or published in any

jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. We and the underwriters require that the persons into whose possession this prospectus supplement comes inform themselves about, and observe any restrictions relating to, the offering and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

We expect that delivery of the subordinated notes will be made against payment therefor on or about June 23, 2020, which will be the fifth business day following the date hereof (such settlement being referred to as “T+5”). Under Rule 15c6-1 of the Exchange Act, trades in the secondary market generally are required to settle in two business days, unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the subordinated notes prior to the delivery of the subordinated notes hereunder will be required, by virtue of the fact that the subordinated notes initially settle in T+5, to specify an alternate settlement arrangement at the time of any such trade to prevent a failed settlement. Purchasers of the subordinated notes who wish to trade the subordinated notes prior to their date of delivery hereunder should consult their advisors.

In relation to each member state of the European Economic Area (the “EEA”), each a Member State, no offer of the subordinated notes to the public has been or will be made in that Member State, except that offers of the subordinated notes to the public may be made in that Member State at any time under the following exemptions under the Prospectus Regulation:

provided that no such offer of subordinated notes shall require us or the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of the above provisions, the expression “an offer of subordinated notes to the public” in relation to any subordinated notes in any Member State means the communication in any form and by any means of sufficient information on the terms of the offer and any subordinated notes to be offered so as to enable an investor to decide to purchase or subscribe for any subordinated notes, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

This document is only being distributed to, and is only directed at, persons in the United Kingdom that are qualified investors within the meaning of Article 2(e) of the Prospectus Regulation that are also (i) investment professionals falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended, referred to herein as the Order, and/or (ii) high net worth entities falling within Article 49(2)(a) to (d) of the Order and other persons to whom it may lawfully be communicated. Each such person is referred to herein as a Relevant Person.

In the United Kingdom, any investment or investment activity to which this prospectus supplement relates is available only to Relevant Persons and will only be engaged with Relevant Persons. This prospectus supplement and its contents are confidential and should not be distributed, published or reproduced (in whole or in part) or disclosed by recipients to any other persons in the United Kingdom. Any person in the United Kingdom that is not a Relevant Person should not act or rely on this document or any of its contents.

Certain legal matters in connection with this offering, including the validity of the subordinated notes offered hereby, will be passed upon for us by Hogan Lovells US LLP. Certain legal matters in connection with this offering will be passed upon for the underwriters by Squire Patton Boggs (US) LLP, Cincinnati, Ohio.

The consolidated financial statements of NBT Bancorp Inc. as of December 31, 2019 and 2018, and for each of the years in the three-year period ended December 31, 2019, and management's assessment of the effectiveness of internal control over financial reporting as of December 31, 2019 have been incorporated by reference herein and in the accompanying prospectus in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.