FINANCIAL INSTITUTIONS INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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FINANCIAL INSTITUTIONS, INC.

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FROM OUR INDEPENDENT BOARD CHAIRFELLOW SHAREHOLDERS:

Thank you, on behalf of the Board of Directors of Financial Institutions, Inc., for your interest and investment in our Company. Our 2025 results were very strong and illustrate the effectiveness of the strategic actions we have taken in recent years and the competitive positioning of our core community banking business lines within our markets. As expected, our fourth quarter 2024 public equity offering and subsequent balance sheet restructuring provided momentum into 2025 and have supported improved earnings and profitability. In addition, our core business operations performed at a high level, resulting in strong top- and bottom-line results. Disciplined execution of community banking fundamentals and continued focus on profitability in a manner that prioritizes safety and soundness remain key focus areas for our Board and executive management team, in support of long-term value creation for our shareholders.

Tangible common book value per share(1) grew to $27.84 as of December 31, 2025, up nearly 14% from one year prior. We recognize that this metric is a practical measure of intrinsic value in a company and we are committed to ensuring the quality of our earnings, a prudent approach to risk management and thoughtful allocation of capital come together to consistently grow tangible common book value over the long term. Accordingly, we will be incorporating this important metric into our long-term incentive plan beginning in 2026, as noted on page 37. We have made prudent investments in people, process and technology, while also efficiently deploying capital through our quarterly cash dividend, which we increased by $0.01, or 3.2%, to $0.32 per outstanding common share in February 2026, and the new share repurchase program that we approved in September 2025. We also took steps to build depth in our Board and plan for the future, through director refreshment, ongoing education, and cross-training. We are pleased to nominate Dave Bovenzi, a seasoned investment professional, and Steve Finch, an experienced operations and manufacturing leader, to our Board this year, as both bring valuable public company board experience. In 2025, we welcomed Angela Panzarella and Bob Schrader to our Board and its Audit Committee. Angela also serves as Vice Chair of our Management Development and Compensation (“MD&C”) Committee. Kim VanGelder was appointed to the MD&C Committee and the Board’s Executive Committee, while Mark Zupan joined our Nominating and Governance Committee, reflecting our approach to cross-training. I would also like to thank Don Boswell for his counsel and leadership during his three terms of service ahead of his retirement from our Board at the upcoming annual meeting.

We greatly value engagement with our shareholders and seek opportunities to proactively engage regularly, through conference attendance, virtual and in-person meetings, and publicly available quarterly earnings calls. Your engagement in our annual meeting is also important, and we encourage you to read this 2026 Proxy Statement and vote online to ensure that you are represented. Thank you again for your support of our Company. Cordially, Susan R. HollidayChair of the BoardApril 6, 2026

(1) Tangible Common Book Value Per Share (“TCBV”) is a non-GAAP financial measure. Please refer to Appendix A for a description of this financial measure and a reconciliation of TCBV to its most directly comparable GAAP financial measure.

Financial Institutions, Inc.

FROM OUR CEOFELLOW SHAREHOLDERS:

Our Company’s 2025 results reflect our consistent and disciplined execution. Strengthened by the strategic initiatives that gave us solid positioning heading into 2025, including the transformative investment securities restructuring we completed in December 2024 that was accompanied by a public equity offering, our core community banking business lines performed at a high level. I’m very proud of what our team accomplished and confident in our ability to continue executing on our strategic priorities in order to deliver a simple, connected and trusted banking experience in the markets we serve, and, importantly, long-term value to our shareholders.Our full year 2025 financial results included net income available to common shareholders of $73.4 million, or $3.61 per diluted share, and return on average assets of 1.20%. Net interest income reached a record level and noninterest income proved durable. We reported net interest margin for 2025 of 3.53%, reflecting 67 basis points of expansion year-

over-year. While the majority of this increase was attributable to the 2024 investment securities restructuring, it also reflects the impacts of our 4% annual loan growth, effective management of funding costs and continued active balance sheet management throughout last year. We closed the year with a successful subordinated debt offering in December 2025 that allowed us to refinance previous sub-debt issuances in January 2026 at a more attractive rate. We have also been executing under the repurchase program our Board approved in 2025, repurchasing 336,869 shares for an average price of $31.98 per share in the fourth quarter of 2025, reflecting our commitment to returning capital to shareholders in an efficient way. Alongside these meaningful accomplishments, the more than 600 employees of our community bank and wealth management firm subsidiaries served our communities through ongoing financial literacy education and volunteerism. We also continued to support local non-profits through grant funding. Details on these efforts and the other ways we seek to give back are outlined in our 2025 Community Report, which is available at Five-StarBank.com.

We cordially invite you to our 2026 Annual Meeting of Shareholders on Wednesday, May 20, 2026, at 10:00 am, Eastern Time. The meeting will be held in virtual format through a live webcast. You will be asked to vote on several items including the election of directors, compensation of our named executive officers (the say-on-pay vote), and the

ratification of the appointment of RSM US LLP to serve as our independent registered public accounting firm for 2026. Your vote is important, and we encourage you to read the proxy statement and vote your shares as promptly as possible. Proxy materials are again being provided via the internet this year, expediting delivery to shareholders, supporting effective expense management and reducing the environmental impact of our meeting. Please find information on how to attend the annual meeting, vote and submit questions in the attached notice of annual meeting.

On behalf of the Company’s executive and senior leadership team, I thank you for your continued support of and investment in Financial Institutions, Inc.Sincerely, Martin K. BirminghamPresident and Chief Executive OfficerApril 6, 2026

Financial Institutions, Inc.