BigCommerce Holdings 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. A reconciliation of our historical Non-GAAP financial measures to the most directly comparable GAAP measures has been provided in the tables below.

Annual Revenue Run-Rate

We calculate annual revenuerun-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-monthnon-recurring and variable revenue, which includesone-time partner integrations, one-time fees, payments revenue share, and any other revenue that isnon-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 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, othernon-operating income and expense and our provision or benefit for income taxes. The most directly comparable GAAP measure is net loss.

Non-GAAP Operating Income (Loss)

We define Non-GAAP operating income (loss) as our GAAP operating loss from operations, 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, amortization of acquisition-related intangible assets, and restructuring charges. The most directly comparable GAAP measure is our loss from operations.

Reconciliation of net loss to adjusted EBITDA:

Reconciliation of loss from operations to Non-GAAP operating income (loss):

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BIGCOMMERCE HOLDINGS, INC. Annual Meeting of Shareholders May 16, 2024 8:00 AM Central Time This proxy is solicited by the Board of Directors The shareholder(s) hereby appoint(s) Brent Bellm, Chief Executive Officer, and Chuck Cassidy, Chief Legal Officer 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 16, 2024, virtually at www.virtualshareholdermeeting.com/BIGC2024, 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