Klaviyo IPO Presentation Deck

GAAP to Non-GAAP reconciliation (cont'd) Non-GAAP Operating Expense (in thousands) Research and Development (R&D) Expense on a GAAP Basis Less: Amortization of Prepaid Marketing Expense Less: Stock-Based Compensation Expense ¹,2 Less: Restructuring 3 Non-GAAP R&D Expense Revenue R&D Expense as a % of Revenue Non-GAAP R&D Expense as a % of Revenue Q1'21 1,599 $14,643 $14,412 $17,293 $13,044 $58,271 25.1% Q2'21 22.4% 1,393 Q3'21 21.5% 2,204 $66,949 $75,876 19.4% 22.8% Q4'21 19.9% 704 $13,019 $15,089 $18,547 $20,893 $23,748 $89,544 Q1'22 $19,251 $21,227 $24,048 $30,090 $28,712 21.5% 20.7% 334 Q2'22 21.4% 300 $99,322 $109,023 21.0% 22.1% Q3'22 21.8% 298 $29,792 $119,168 25.3% 25.0% ¹ Represents non-cash share-based awards granted. Stock-based compensation expense of $1.5 million for the quarter ending December 31, 2022 related to the cancellation of an executive's unvested RSUS outstanding for which the service-based vesting condition was satisfied but the liquidity-based vesting condition was not, which was paid in cash, and thus is excluded from the table above. This is included within general and administrative expense. Q4'22 2 Represents non-cash share-based awards granted. Stock-based compensation expense of $16.7 million related to repurchasing and retiring our common stock was paid in cash, thus excluded from the table above. 3 Represents restructuring costs incurred in connection with a reduction in the Company's workforce announced in March 2023. During the period ended March 31, 2023, stock-based compensation expense of approximately $0.5 million related to the reduction in workforce is excluded from restructuring expense and included in stock-based compensation from the table above. 298 Q1'23 19.8% 19.6% $35,032 $33,055 $28,414 $31,181 551 3,300 $145,235 $156,088 22.4% 20.0% 2023 Ⓒ Klaviyo Q2'23 262 $32,793 Confidential $164,586 20.1% 19.9% 57

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