Commerce.com, Inc.

Use of Non-GAAP Financial Measures

We have provided in this Proxy Statement certain financial information that has not been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). Our management uses these Non-GAAP financial measures internally in analyzing our financial results and believes that use of these Non-GAAP financial measures is useful to investors as an additional tool to evaluate ongoing operating results and trends and in comparing our financial results with other companies in our industry, many of which present similar Non-GAAP financial measures. Non-GAAP financial measures are not meant to be considered in isolation or as a substitute for comparable financial measures prepared in accordance with GAAP and should be read only in conjunction with our consolidated financial statements prepared in accordance with GAAP.

Annual Revenue Run-Rate

We calculate annual revenue run-rate (“ARR”) at the end of each month as the sum of: (1) contractual monthly recurring revenue at the end of the period, which includes platform subscription fees, invoiced growth adjustments, feed management subscription fees, recurring professional services revenue, and other recurring revenue, multiplied by twelve to prospectively annualize recurring revenue, and (2) the sum of the trailing twelve-month non-recurring and variable revenue, which includes one-time partner integrations, one-time fees, payments revenue share, and any other revenue that is non-recurring and variable. ARR does not have any standardized meaning and is therefore unlikely to be comparable to similarly titled measures presented by other companies. ARR should be viewed independently of revenues and deferred revenues and is not intended to be combined with or to replace either of those items. ARR is not a forecast and the active contracts at the end of a reporting period used in calculating ARR may or may not be extended or renewed by our clients.

Adjusted EBITDA

We define Adjusted EBITDA as our GAAP net loss, excluding the impact of stock-based compensation expense and associated payroll tax costs, third party acquisition-related costs, and other acquisition related expenses, including contingent compensation arrangements entered into in connection with acquisitions, depreciation, amortization of acquisition-related intangible assets, interest income, interest expense, restructuring charges, other non-operating income and expense and our provision or benefit for income taxes. The most directly comparable GAAP measure is net loss.

Reconciliation of net loss to Adjusted EBITDA:

SCAN TO VIEW MATERIALS & VOTE BIGCOMMERCE HOLDINGS, INC. 11305 FOUR POINTS DRIVE BUILDING 2, SUITE 100 AUSTIN, TX 78726 VOTE BY INTERNET - www.proxyvote.com or scan the QR Barcode above Use the Internet to transmit your voting instructions and for electronic delivery of information up until 11:59 p.m. Eastern Time on May 14, 2025. Have your proxy card in hand when you access the web site and follow the instructions to obtain your records and to create an electronic voting instruction form. During The Meeting - Go to www.virtualshareholdermeeting.com/BIGC2025 You may attend the meeting via the Internet and vote during the meeting. Have the information that is printed in the box marked by the arrow available and follow the instructions. VOTE BY PHONE - 1-800-690-6903 Use any touch-tone telephone to transmit your voting instructions up until 11:59 p.m. Eastern Time on May 14, 2025. Have your proxy card in hand when you call and then follow the instructions. VOTE BY MAIL Mark, sign and date your proxy card and return it in the postage-paid envelope we have provided or return it to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, NY 11717. TO VOTE, MARK BLOCKS BELOW IN BLUE OR BLACK INK AS FOLLOWS: KEEP THIS PORTION FOR YOUR RECORDS DETACH AND RETURN THIS PORTION ONLY THIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED. The Board of Directors recommends you vote FOR the following: For Withhold For All All All Except To withhold authority to vote for any individual nominee(s), mark “For All Except” and write the number(s) of the nominee(s) on the line below. 1. Election of Directors Nominees 01) Sally Gilligan 02) Satish Malhotra The Board of Directors recommends you vote FOR Proposals 2 and 3. For Against Abstain 2. Ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm for 2025. 3. Non-binding advisory vote to approve the compensation of our named executive officers. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. Please sign exactly as your name(s) appear(s) hereon. When signing as attorney, executor, administrator, or other fiduciary, please give full title as such. Joint owners should each sign personally. All holders must sign. If a corporation or partnership, please sign in full corporate or partnership name by authorized officer. Signature [PLEASE SIGN WITHIN BOX] Date Signature (Joint Owners) Date 0000665287_1 R1.0.0.2

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice and Proxy Statement and Form 10-K are available at www.proxyvote.com BIGCOMMERCE HOLDINGS, INC. Annual Meeting of Shareholders May 15, 2025 8:00 AM Central Time This proxy is solicited by the Board of Directors The shareholder(s) hereby appoint(s) Travis Hess, Chief Executive Officer, and Chuck Cassidy, General Counsel and Secretary, or either of them, as proxies, each with the power to appoint his substitute, and hereby authorize(s) them to represent and to vote, as designated on the reverse side of this ballot, all of the shares of common stock of BIGCOMMERCE HOLDINGS, INC. that the shareholder(s) is/are entitled to vote at the Annual Meeting of Shareholders to be held at 8:00 AM Central Time on May 15, 2025, virtually at www.virtualshareholdermeeting.com/BIGC2025, and any adjournment or postponement thereof. This proxy, when properly executed, will be voted in the manner directed herein. If no such direction is made, this proxy will be voted in accordance with the Board of Directors' recommendations. Continued and to be signed on reverse side 0000665287_2 R1.0.0.2