BLMT Bsb Bancorp, Inc.

Proposal 4 — Frequency of Advisory Votes On Executive Compensation

In accordance with Section 14A of the Exchange Act, we are providing a shareholder advisory vote to approve the compensation of our Named Executive Officers (the “say-on-pay” advisory vote in Proposal 3 of the Proxy Statement) this year, and we will do so at least once every three years. Pursuant to Section 14A of the Exchange Act, at the 2018 Annual Meeting we are also asking stockholders to vote on a Say-On-Frequency Proposal regarding whether future “say-on-pay” advisory votes on executive compensation should occur every year, every two years or every three years.

After careful consideration, the Board of Directors recommends that future stockholder “say-on-pay” advisory votes on executive compensation be conducted every year. Although the Board of Directors recommends a “say-on-pay” vote every year, stockholders will be able to specify one of four choices for this proposal on the proxy card: one year, two years, three years or abstain. Shareholders are not voting to approve or disapprove of the Board of Directors’ recommendation.

Although the vote on this Say-On-Frequency Proposal is non-binding on the Board of Directors, the Board of Directors and the Compensation Committee will review the voting results and take them into consideration when deciding how often to conduct future say-on-pay stockholder advisory votes.

The Board of Directors unanimously recommends that you vote “FOR” the One Year frequency option. Unless otherwise instructed, validly executed proxies will be voted “FOR” the One Year frequency option.

Vote Required on Proposal 4

In voting on the advisory, non-binding vote on how frequently a stockholder vote on executive compensation matters should be held, you may vote in favor of holding such a vote once every year, once every two years or once every three years, or you may abstain from voting. Even though this vote will not be binding on the Board of Directors, and it will not create or imply any change in the fiduciary duties of or impose any additional fiduciary duty on the Board of Directors, the Board of Directors will take into account the outcome of this vote in making a determination on the frequency that advisory votes on our executive compensation will be included in our proxy statements. In counting votes on the advisory, non-binding proposal on how frequently to hold a stockholder vote on our executive compensation, abstentions and broker non-votes will have no effect on the outcome of the vote.

Voting by Proxy; Revocability of Proxy

If you sign and return the amended proxy card, it will revoke and replace any previous proxy you have submitted. If you do not sign and return the amended proxy card, your previous proxy will remain in effect, but it will not include any vote on the Say-On-Frequency Proposal.

If the amended proxy card or original proxy card is properly signed, dated and returned and is not revoked, the proxy will be voted at the Meeting in accordance with the stockholder’s instructions indicated on the proxy. If you sign, date and return a proxy card without giving voting instructions, your shares will be voted as recommended by the Company’s Board of Directors. The Board of Directors recommends that you vote:

You may revoke your proxy at any time before the vote is taken at the meeting. To revoke your proxy, you must advise the Corporate Secretary of the Company in writing before your common stock has been voted at the annual meeting, deliver a later dated proxy, vote on a later date by telephone or the Internet or attend the meeting and vote your shares in person by ballot. Attendance at the annual meeting will not in itself constitute revocation of your proxy.

If you are the beneficial owner of shares held in “street name,” your bank, broker or other nominee has forwarded you this Supplement and the amended proxy card. As the beneficial owner of the shares, you have the right to direct your nominee concerning how to vote your shares by using the voting instructions your nominee included in the mailing or by following your nominee’s instructions for voting. If you want to vote your shares in person at the Meeting, you must contact your nominee directly in order to obtain a proxy issued to you by your nominee holder. If you are a “street name” holder, contact your bank, broker or other nominee so that they can provide instructions explaining how you may change or revoke your voting instructions.

. IMPORTANT ANNUAL MEETING INFORMATION Using a black ink pen, mark your votes with an X as shown in this example. Please do not write outside the designated areas. X Annual Meeting Proxy Card • PLEASE FOLD ALONG THE PERFORATION, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. • Proposals — THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” EACH OF THE FIRST THREE LISTED PROPOSALS, AND A VOTE TO HOLD AN ADVISORY, NON-BINDING VOTE EVERY “ONE YEAR” IN VOTING ON THE FOURTH PROPOSAL. 1. Election of Directors: For Withhold For Withhold For Withhold + 01 - Robert M. Mahoney 02 - John A. Borelli 03 - John W. Gahan, III 04 - John A. Whittemore For Against Abstain For Against Abstain 2. The ratification of the appointment of Baker Newman 3. An advisory, non-binding vote to approve the compensation & Noyes, LLC as independent registered public of the Company’s named executive officers. accounting firm of BSB Bancorp, Inc. for the fiscal year ending December 31, 2018. 1 Year 2 Years 3 Years Abstain 4. An advisory, non-binding vote regarding the frequency of voting on our executive compensation. Authorized Signatures — This section must be completed for your vote to be counted. — Date and Sign Below Please sign exactly as name(s) appears hereon. Joint owners should each sign. When signing as attorney, executor, administrator, corporate officer, trustee, guardian, or custodian, please give full title. Date (mm/dd/yyyy) — Please print date below. Signature 1 — Please keep signature within the box. Signature 2 — Please keep signature within the box. 1UPX + 02UDFB

. IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE ANNUAL MEETING OF STOCKHOLDERS TO BE HELD ON MAY 23, 2018—THIS NOTICE, THE PROXY STATEMENT, AND BSB BANCORP, INC.’S 2017 ANNUAL REPORT TO STOCKHOLDERS ARE EACH AVAILABLE AT http://www.edocumentview.com/BLMT • PLEASE FOLD ALONG THE PERFORATION, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. • Proxy — BSB BANCORP, INC. Notice of 2018 Annual Meeting of Stockholders Belmont Town Hall, Board of Selectman’s Meeting Room, 455 Concord Avenue, 2nd Floor, Belmont, MAProxy Solicited by Board of Directors for Annual Meeting — May 23, 2018 The undersigned hereby appoints the official proxy committee of BSB Bancorp, Inc. (the “Company”), consisting of Robert J. Morrissey and S. Warren Farrell or either of them, with full power of substitution in each, to act as proxy for the undersigned, and to vote all shares of common stock of the Company which the undersigned is entitled to vote only at the Annual Meeting of Stockholders to be held on Wednesday, May 23, 2018 at 10:00 a.m., Eastern Daylight Time, at the Belmont Town Hall, Board of Selectman’s Meeting Room, 455 Concord Avenue, 2nd Floor, Belmont, and at any and all adjournments thereof, with all of the powers the undersigned would possess if personally present at such meeting as follows: THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” EACH OF THE FIRST THREE LISTED PROPOSALS, AND A VOTE TO HOLD AN ADVISORY, NON-BINDING VOTE EVERY “ONE YEAR” IN VOTING ON THE FOURTH PROPOSAL. This proxy is revocable and will be voted as directed, but if no instructions are specified, this proxy, properly signed and dated, will be voted “FOR” each of the first three proposals listed, and to hold an advisory, non-binding vote every “ONE YEAR” on the fourth proposal. If other business is presented at the Annual Meeting, including whether or not to adjourn the meeting, this proxy will be voted by the proxies in their judgment. At the present time, the Board of Directors knows of no other business to be presented at the Annual Meeting. This proxy also confers discretionary authority on the proxy committee of the Board of Directors to vote (1) with respect to the election of any person as director, where the nominees are unable to serve or for good cause will not serve and (2) matters incident to the conduct of the meeting. In their discretion, the Proxies are authorized to vote upon such other business as may properly come before the meeting. PLEASE COMPLETE, DATE, SIGN AND PROMPTLY MAIL THIS PROXY IN THE ENCLOSED POSTAGE-PAID ENVELOPE. (Items to be voted appear on reverse side.)