five9q22025investorprese

Q2 2025 Investor Presentation Five9 (NASDAQ: FIVN)

©Five9, Inc. All rights reserved. | 2 Safe Harbor This presentation is proprietary and is intended solely for the information of the persons to whom it is presented. Disclosure of this presentation, its contents, extracts or abstracts to third parties is not authorized without the express written permission of Five9, Inc. (the “Company”), and it may not be retained, reproduced or distributed, in whole or in part, by any means (including electronic) without the prior written consent of Five9, Inc. This presentation speaks only as the date of first publication, its availability after such date shall not constitute an express or implied confirmation of such information as of any later date, and the Company undertakes no obligation to update any of the information set forth herein. This presentation includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, concerning events, trends, expectations and beliefs that may affect our industry or the Company, including long- term competitive position of the company, future financial performance of the company, customer growth, industry size and trends, our expectations regarding macroeconomic challenges, company market position, initiatives, pipeline, technology and product initiatives, including R&D, AI and automation and their expected benefits to the Company, potential growth drivers, projections and guidance concerning our future results of operations including our long-term model, our market opportunity and our long-term growth prospects. The Company has based these forward-looking statements on its current expectations and projections about future events and financial and operating trends that it believes may affect its financial condition, results of operations, business strategy, short- term and long-term business operations and objectives, and financial needs. Our actual results may be materially different from what we discuss here and you should not unduly rely on such forward looking statements. Please refer to our most recent Form 10-K and 10-Q under the caption "Risk Factors" and elsewhere in such reports, for detailed information about factors that could cause our results to differ from those set forth in such forward-looking statements, including risks related to the impact of adverse economic conditions, including the impact of macroeconomic challenges, the impact of global tariff increases and potential increases and announcements regarding the same, continued inflation, uncertainty regarding consumer spending, high interest rates, fluctuations in currency exchange rates, the impact of the Russia-Ukraine conflict, the impact of the conflicts in the Middle East, lower growth rates within our installed base of customers, competition, the effect of AI on the CX market, the Company’s AI platform and its market position and expected impact on the Company’s growth, expansion of the Company’s international operations, and other factors. Past performance is not necessarily indicative of future results. In addition to U.S. GAAP financials, this presentation includes certain non-GAAP financial measures. These non-GAAP financial measures are in addition to, and not a substitute for or superior to, measures of financial performance prepared in accordance with U.S. GAAP and may differ from non-GAAP measures used by other companies in our industry. The Company considers these non-GAAP financial measures to be important because they provide useful measures of the operating performance of the Company, exclusive of unusual events, as well as factors that do not directly affect what we consider to be our core operating performance. The non-GAAP financial measures should not be considered a substitute for financial information presented in accordance with GAAP. Please see the reconciliation of non-GAAP financial measures to the most directly comparable GAAP measure set forth in the Appendix to this presentation. This presentation contains statistical data that we obtained from industry publications and reports generated by third parties. Although we believe that the publications and reports are reliable, we have not independently verified this statistical data and accordingly, we cannot guarantee their accuracy or completeness.

©Five9, Inc. All rights reserved. | 3 Q2’25 Results and Key Metrics 12% Total Revenue YoY Growth 16% Subscription Revenue YoY Growth 81% Subscription Revenue as % of Total 20% LTM Enterprise Subscription Revenue YoY Growth 90% LTM Enterprise Revenue as % of Total 63% Adjusted Gross Margin 24% (All-time High) Adjusted EBITDA Margin 63% Adjusted EBITDA YoY $ Growth 12% Operating Cash Flow Margin 8% Free Cash Flow Margin 108% LTM DBRR Highest Total Quarterly ACV Bookings in Two Years (excluding the one Q1’24 Financial Services mega deal) All-time High Installed Base Bookings In co m e St a te m en t C a sh Fl ow Note: Non-GAAP and adjusted metrics exclude depreciation, intangibles amortization, stock-based compensation and unusual expense items. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure O p er a ti on a l

©Five9, Inc. All rights reserved. | 4 Q2’25 AI Metrics and Innovation 42% Enterprise AI Revenue YoY Growth 10% AI as % of Enterprise Subscription Revenue 20%+ AI as % of Enterprise New Logo ACV Bookings Virtually All AI Attach on $1M+ ARR New Logo Deals 3x+ Enterprise AI Bookings YoY Growth 2x+ Enterprise AI New Logo Bookings YoY Growth 4x+ Enterprise AI Installed Base Bookings YoY Growth Agentic AI Agents Launched in Q2’25 AI Trust & Governance Launched in Q2’25 Best AI Ranked as Having the Best AI Solutions by Channel Partners(1) M et ri cs In no va ti on (1) Source: Semi-Annual Baird Survey from July 2025

©Five9, Inc. All rights reserved. | 5 Q2’25 AI Customer Examples C us to m er E xa m p le s (1) Anticipated ARR Key Drivers of Momentum View Five9 as their core CX platform, including AI View Five9 as their core CX platform with the AI expertise, products and integrations Achieving significant and tangible ROI with Five9’s AI solutions Customer #1 Healthcare company Customer #3 Airline company Customer #5 Healthcare company Outcome Extended contract to 5-year term Expanded AI portfolio after working with Five9 AI experts to evaluate ROI of increasing self-service capabilities - 80% reduction in abandonment rate - 50%+ increase in containment rate - 60%+ improvement in post interaction work time Increase in Five9 ARR(1) ~40% ($11M+) 2x+ ($7M+) Customer #2 Healthcare company Customer #4 Pest Control company Customer #6 Digital Health company Outcome Extended contract to 5-year term Added new AI capabilities - 19% improvement in self-service containment - Improvement in CSAT metrics - 50% reduction in abandonment rate - ~50% reduction in hold time Increase in Five9 ARR(1) 2x+ ($5M+) 30%+ ($4M+) 1 2 3

©Five9, Inc. All rights reserved. | 6 Key Customer Wins and Expansion New Customer #2 Business unit of Fortune 50 financial services company Chose Five9 to replace legacy systems and enable scalable, compliant voice solutions integrated with Salesforce $2.8M in anticipated ARR New Customer #3 National mortgage services provider Chose Five9 to modernize from an inflexible on-prem system that was contributing to client churn, to a cloud platform that could support inbound and outbound engagement, integrate with a complex CRM stack, and elevate their customer experience $1.2M in anticipated ARR New Customer #4 Global veterinary services provider Chose Five9 to consolidate fragmented on-prem systems and elevate both customer and agent experience by unifying on a modern cloud platform, activating voice and all digital channels to manage workflows and gain visibility into performance trends $1.1M in anticipated ARR Existing Customer Leading academic health system Expanded its partnership with Five9 and signed new five-year agreement with a focus on enhancing their AI Agent solution, integrating Five9 with Epic to streamline clinical workflows, and leveraging Five9 Fusion for Salesforce $3.0M in additional ARR to over $5.0M total ARR New Customer #1 Global data and analytics company Chose Five9 to modernize from a rigid legacy platform to a scalable, AI-powered CX solution to elevate customer engagement and drive operational efficiency $3.3M in anticipated ARR (1) Announced on 5/1/2025 Five9 Earnings Call (1)

©Five9, Inc. All rights reserved. | 7 Consistent Revenue Growth 95 100 112 128 138 144 154 174 183 189 198 208 218 223 230 239 247 252 264 279 280 283 Quarterly Revenue ($M) Annual Revenue ($M) 12% YoY Growth 258 328 435 610 779 910 1,042 2018 2019 2020 2021 2022 2023 2024 14% YoY Growth

©Five9, Inc. All rights reserved. | 8 High Customer Retention % Annual Dollar Based Retention Rate (DBRR) Note: Annual DBRR based on last 12 months at the end of each respective quarter 111% 111% 114% 117% 121% 123% 123% 122% 120% 118% 118% 115% 114% 112% 110% 110% 109% 108% 108% 108% 107% 108% Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25

©Five9, Inc. All rights reserved. | 9 Executing on Enterprise Opportunity Note: Historical results prior to 2018 based on ASC 605; Results 2018 onward are based on ASC 606; $1M+ ARR based on Q4’24 annualized 60% 90% Q2'14 (IPO) Q2'25 Enterprise Customers $1M+ ARR (Q4’24 Ann.)Enterprise as a % of Total Revenue (LTM) 3 211 Q2'14 (IPO) Q4'24

©Five9, Inc. All rights reserved. | 10 $150.2 $152.4 $163.3 $176.8 $174.6 $178.5 14% 11% 17% 21% 16% 17% 0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0% 35.0% 40.0% 45.0% 50.0% $0.0 $50.0 $100.0 $150.0 $200.0 $250.0 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 Adjusted Gross Profit ($M) Adjusted Gross Profit YoY Growth (%) 60.8% 60.5% 61.8% 63.5% 62.4% 63.0% 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% Adjusted Gross Margin (%) Continued Adjusted Gross Profit Expansion Non-GAAP Adjusted Gross Profit and Margin ($M) Note: Adjusted gross profit and adjusted gross margin excludes depreciation, intangibles amortization, stock-based compensation and unusual expense items. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure

©Five9, Inc. All rights reserved. | 11 Robust Margin Expansion and Operating Leverage Non-GAAP Note: Non-GAAP and adjusted metrics exclude depreciation, intangibles amortization, stock-based compensation and unusual expense items. Historical results prior to 2018 based on ASC 605; Results 2018 onward are based on ASC 606. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure 20.4% 9.7% 37.5% 22.6% 21.4% 6.8% 79.3% 39.0% Q2'14 (IPO) Q2'25 G&A S&M R&D Non-GAAP Opex (% of revenue) 40.3% point improvement 51.5% 63.0% Q2'14 (IPO) Q2'25 Adj. Gross Margin 11.5% point expansion (27.8%) 24.0% Q2'14 (IPO) Q2'25 Adj. EBITDA Margin 51.8% point expansion

©Five9, Inc. All rights reserved. | 12 Improvement in Stock-Based Compensation Expense Stock-Based Compensation Expense Total, In-Year and Prior Periods (% of Revenue) 17% 19% 13% 13% 5% 4% 3% 2% 22% 23% 16% 14% 2022 2023 2024 YTD Q2'25 Prior Periods In-Year Total

©Five9, Inc. All rights reserved. | 13 Continuing to Drive Balanced Growth Note: Adjusted EBITDA excludes depreciation, intangibles amortization, stock-based compensation and unusual expense items. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure; ASC 605 for periods prior to 2018 22% 23% 20% 25% 23% 25% 27% 26% 28% 27% 23% 24% 23% 22% 25% 25% 28% 30% 31% 27% 27% 28% 28% 28% 29% 34% 39% 45% 44% 38% 36% 33% 32% 29% 20% 20% 18% 16% 15% 13% 13% 15% 17% 13% 12% (28%) (19%) (15%) (10%) (7%) (3%) 3% 1% 6% 7% 7% 6% 6% 10% 12% 13% 16% 20% 23% 16% 19% 18% 21% 15% 18% 21% 23% 16% 17% 18% 21% 13% 17% 18% 22% 16% 19% 18% 20% 15% 17% 20% 23% 19% 24% (6%) 3% 4% 14% 15% 21% 31% 27% 34% 34% 29% 29% 29% 33% 38% 38% 44% 50% 53% 42% 45% 46% 49% 42% 47% 55% 61% 61% 61% 55% 57% 46% 49% 47% 42% 36% 36% 34% 35% 28% 30% 35% 40% 32% 36% Q 2' 14 Q 3' 14 Q 4' 14 Q 1' 15 Q 2' 15 Q 3' 15 Q 4' 15 Q 1' 16 Q 2' 16 Q 3' 16 Q 4' 16 Q 1' 17 Q 2' 17 Q 3' 17 Q 4' 17 Q 1' 18 Q 2' 18 Q 3' 18 Q 4' 18 Q 1' 19 Q 2' 19 Q 3' 19 Q 4' 19 Q 1' 20 Q 2' 20 Q 3' 20 Q 4' 20 Q 1' 21 Q 2' 21 Q 3' 21 Q 4' 21 Q 1' 22 Q 2' 22 Q 3' 22 Q 4' 22 Q 1' 23 Q 2' 23 Q 3' 23 Q 4' 23 Q 1' 24 Q 2' 24 Q 3' 24 Q 4' 24 Q 1' 25 Q 2' 25 % YoY Revenue Growth % EBITDA Margin

©Five9, Inc. All rights reserved. | 14 Operating and Free Cash Flow $118.5 $125.8 $174.5 14.0% 13.0% 15.8% (40.0%) (30.0%) (20.0%) (10.0%) 0.0% 10.0% 20.0% $0.0 $50.0 $100.0 $150.0 $200.0 Q2'23 Q2'24 Q2'25 Operating Cash Flow % Operating Cash Flow Margin LTM Operating Cash Flow ($M) DSO of 35 days in Q2’25 LTM Free Cash Flow ($M) $78.0 $78.3 $109.9 9.2% 8.1% 9.9% (5.0%) (3.0%) (1.0%) 1.0% 3.0% 5.0% 7.0% 9.0% 11.0% $0.0 $20.0 $40.0 $60.0 $80.0 $100.0 $120.0 $140.0 $160.0 $180.0 $200.0 Q2'23 Q2'24 Q2'25 Free Cash Flow % Free Cash Flow Margin Note: Free cash flow defined as operating cash flow less CAPEX less capitalized software; Non-GAAP and adjusted metrics exclude depreciation, intangibles amortization, stock-based compensation and unusual expense items. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure

©Five9, Inc. All rights reserved. | 15Source: Company estimates; Gartner estimates; MZA estimates; Statista estimates Note: TAM as of 7/31/2025 based on Company estimates, Gartner estimates, MZA estimates, and Statista estimates TAM Expansion Driven by AI $234B $24B Cloud Contact Center Software + $210B Contact Center Labor Spend $24B Cloud Contact Center Software

©Five9, Inc. All rights reserved. | 16 Q3’25 and 2025 Guidance Note: Refer to the “GAAP to Non-GAAP Net Income (Loss) Reconciliation – Guidance” table in the appendix for more details, including important assumptions upon which such guidance is based; Non-GAAP and adjusted metrics exclude depreciation, intangibles amortization, stock-based compensation and unusual expense items Q3’25 2025 Revenue $283.0M – $286.0M $1.1435B – $1.1495B GAAP Net Income Per Diluted Share $0.06 – $0.12 $0.23 – $0.30 Non-GAAP Net Income Per Diluted Share $0.72 – $0.74 $2.86 – $2.90 Diluted Shares – GAAP 87.5M 88.5M Diluted Shares – Non-GAAP 78.1M 77.7M Taxes – Non-GAAP $2.8M – $3.0M $7.3M – $7.5M Purchase of PP&E $13M – $14M $26M – $27M

©Five9, Inc. All rights reserved. | 17 Medium-Term Operating Model Today Q2’25 Revenue (YoY Growth) Total Revenue 12% Profit & Expenses (% of Revenue) Adj. Gross Margin 63% S&M 23% R&D 10% G&A 7% Adj. EBITDA 24% Stock-Based Compensation 15% Note: Non-GAAP and adjusted metrics exclude depreciation, intangibles amortization, stock-based compensation and unusual expense items. See appendix for reconciliation of non-GAAP measures to most comparable GAAP measure. Medium-term model assumes stable macroeconomic conditions in 2026 and 2027 Medium-Term Model (In 2027) Key Assumptions Revenue (YoY Growth) 10% - 15% • Assumes stable macro conditions • Potential further upside with AI Profit & Expenses (% of Revenue) 66% - 68%+ • Subscription margin expansion and increasing subscription revenue mix 22% - 23% • Cost discipline • Economies of scale • Key strategic investments in go-to-market and innovation 10% - 11% 6% - 7% 25% - 30%+ • Rule of 40+ in 2027 Ongoing decline as % of revenue • Lagging indicator • Increased discipline

©Five9, Inc. All rights reserved. | 19 Balance Sheet Summary (1) Total principal amount of debt in the amount of $747.5M as of June 30, 2025 will become due in March 2029. Total principal amount of debt in the amount of $434.4M matured on June 1, 2025, and the Company settled its obligations with respect to this note in cash in connection therewith. $ in Millions Quarter Ended June 30, 2025 December 31, 2024 Cash, cash equivalents and marketable investments $635.9 $1,006.0 Working capital 692.6 606.9 Total assets 1,704.9 2,051.2 Total debt¹ 733.6 1,165.3 Total stockholders’ equity 717.4 622.2

©Five9, Inc. All rights reserved. | 20 GAAP to Adjusted Gross Profit Reconciliation Q2’14 – Q4’17 Quarter Ended Q2'14 Q3'14 Q4'14 Q1'15 Q2'15 Q3'15 Q4'15 Q1'16 Q2'16 Q3'16 Q4'16 Q1'17 Q2'17 Q3'17 Q4'17 GAAP gross profit $ 11,216 $ 12,365 $ 13,734 $ 15,496 $ 16,004 $ 17,475 $ 20,398 $ 21,405 $ 22,122 $ 23,192 $ 28,437 $ 27,043 $ 27,454 $ 29,584 $ 33,040 % GAAP gross margin 45.4 % 47.8 % 48.6 % 51.2 % 52.9 % 54.1 % 56.6 % 56.3 % 56.9 % 56.6 % 64.3 % 57.5 % 57.5 % 59.1 % 59.6 % Depreciation & amortization 1,373 1,272 1,291 1,439 1,558 1,470 1,483 1,680 1,616 1,668 1,608 1,576 1,716 1,397 1,611 Stock-based compensation 121 158 176 188 218 233 227 265 329 357 424 434 575 599 594 One-time integration costs — — — — — — — — — — — — — — — Reversal of accrued federal fees — — — — — — — — — — (3,114) — — — — Out of period adj. for accrued federal fees — — 235 — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Adjusted gross profit $ 12,710 $ 13,795 $ 15,436 $ 17,123 $ 17,780 $ 19,178 $ 22,108 $ 23,350 $ 24,067 $ 25,217 $ 27,355 $ 29,053 $ 29,745 $ 31,580 $ 35,245 % adjusted gross margin 51.5 % 53.3 % 54.6 % 56.6 % 58.7 % 59.4 % 61.4 % 61.4 % 61.9 % 61.5 % 61.9 % 61.8 % 62.3 % 63.1 % 63.6 % Note: Historical results prior to 2018 based on ASC 605

©Five9, Inc. All rights reserved. | 21 GAAP to Adjusted Gross Profit Reconciliation Q1’18 – Q4’21 Quarter Ended Q1'18 Q2'18 Q3'18 Q4'18 Q1'19 Q2'19 Q3'19 Q4'19 Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 GAAP gross profit $ 34,203 $ 36,306 $ 39,125 $ 43,996 $ 43,687 $ 46,188 $ 49,297 $ 54,323 $ 55,051 $ 57,339 $ 65,582 $ 76,652 $ 78,079 $ 79,387 $ 87,191 $ 93,835 % GAAP gross margin 58.1 % 59.4 % 59.9 % 60.8 % 58.6 % 59.6 % 58.8 % 58.9 % 57.9 % 57.5 % 58.5 % 59.9 % 56.6 % 55.2 % 56.5 % 54.1 % Depreciation & amortization 1,794 1,864 2,021 2,129 2,366 2,504 2,602 3,384 3,940 5,120 5,171 5,948 7,087 7,825 7,658 8,301 Stock-based compensation 678 853 860 942 1,229 1,658 1,702 1,745 1,989 2,499 2,603 2,331 3,105 3,781 3,994 6,854 One-time integration costs — — — — — — — — — — — — 30 2 37 43 Reversal of accrued federal fees — — — — — — — — — — — — — — — — Out of period adj. for accrued federal fees — — — — — — — — — — — — — — — — Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — 618 — — — — — — Refund for prior year overpayment of USF fees — — — — — — — — — — — — — — — — Adjusted gross profit $ 36,675 $ 39,023 $ 42,006 $ 47,067 $ 47,282 $ 50,350 $ 53,601 $ 59,452 $ 60,980 $ 65,576 $ 73,356 $ 84,931 $ 88,301 $ 90,995 $ 98,880 $ 109,033 % adjusted gross margin 62.3 % 63.8 % 64.3 % 65.1 % 63.4 % 65.0 % 64.0 % 64.4 % 64.1 % 65.7 % 65.4 % 66.4 % 64.0 % 63.3 % 64.1 % 62.8 %

©Five9, Inc. All rights reserved. | 22 GAAP to Adjusted Gross Profit Reconciliation Q1’22 – Q2’25 Quarter Ended Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 GAAP gross profit $ 93,910 $ 101,153 $ 104,231 $ 112,051 $ 113,683 $ 118,521 $ 119,025 $ 126,569 $ 132,480 $ 133,672 $ 142,249 $ 155,997 $ 153,732 $ 155,404 % GAAP gross margin 51.4 % 53.4 % 52.6 % 53.8 % 52.0 % 53.2 % 51.7 % 52.9 % 53.6 % 53.0 % 53.8 % 56.0 % 55.0 % 54.9 % Depreciation & amortization 8,500 8,747 8,904 8,803 8,907 9,269 10,075 10,308 9,613 10,421 10,414 12,087 11,883 12,161 Stock-based compensation 7,793 8,538 8,329 8,638 9,333 9,888 9,856 9,182 7,603 7,789 7,512 6,921 7,184 7,296 One-time integration costs 48 80 187 86 34 — — — 53 72 94 40 — — Reversal of accrued federal fees — — — — — — — — — — — — — — Out of period adj. for accrued federal fees — — — — — — — — — — — — — — Exit costs related to closure and relocation of Russian operations 380 3 96 219 23 51 18 12 — — — — — — Lease amortization for finance leases — — — — — — 492 449 457 455 895 1,802 1,816 2,119 Costs related to reduction in force plan — — — — — — — — — — 2,115 — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — 1,565 Refund for prior year overpayment of USF fees — (3,511) — — — — — — — — — — — — Adjusted gross profit $ 110,631 $ 115,010 $ 121,747 $ 129,797 $ 131,980 $ 137,729 $ 139,466 $ 146,520 $ 150,206 $ 152,409 $ 163,279 $ 176,847 $ 174,615 $ 178,545 % adjusted gross margin 60.5 % 60.7 % 61.4 % 62.3 % 60.4 % 61.8 % 60.6 % 61.3 % 60.8 % 60.5 % 61.8 % 63.5 % 62.4 % 63.0 %

©Five9, Inc. All rights reserved. | 23 GAAP to Adjusted Gross Profit Reconciliation 2014 – 2024 Year Ended 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 GAAP gross profit $ 48,441 $ 69,373 $ 95,156 $ 117,121 $ 153,630 $ 193,495 $ 254,624 $ 338,492 $ 411,345 $ 477,798 $ 564,398 % GAAP gross margin 47.0 % 53.8 % 58.7 % 58.5 % 59.6 % 59.0 % 58.5 % 55.5 % 52.8 % 52.5 % 54.2 % Depreciation & amortization 5,138 5,950 6,573 6,300 7,808 10,856 20,179 30,870 34,955 38,559 42,535 Stock-based compensation 542 866 1,375 2,202 3,333 6,334 9,422 17,734 33,297 38,259 29,825 Reversal of accrued federal fees — — (3,114) — — — — — — — — Out of period adj. for accrued federal fees 235 — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — 618 — — — — One-time integration costs — — — — — — — 112 401 34 259 Exit costs related to closure and relocation of Russian operations — — — — — — — — 698 105 — Refund for prior year overpayment of USF fees — — — — — — — — (3,511) — — Lease amortization for finance leases — — — — — — — — — 941 3,609 Costs related to a reduction in force plan — — — — — — — — — — 2,115 Adjusted gross profit $ 54,356 $ 76,189 $ 99,990 $ 125,623 $ 164,771 $ 210,685 $ 284,843 $ 387,208 $ 477,185 $ 555,696 $ 642,741 % adjusted gross margin 52.7 % 59.1 % 61.7 % 62.7 % 63.9 % 64.2 % 65.5 % 63.5 % 61.3 % 61.0 % 61.7 % Note: Historical results prior to 2018 based on ASC 605

©Five9, Inc. All rights reserved. | 24 GAAP Net Inc. (Loss) to Adj. EBITDA Reconciliation Q2’14 – Q4’17 Note: Historical results prior to 2018 based on ASC 605 Quarter Ended Q2'14 Q3'14 Q4'14 Q1'15 Q2'15 Q3'15 Q4'15 Q1'16 Q2'16 Q3'16 Q4'16 Q1'17 Q2'17 Q3'17 Q4'17 GAAP net income (loss) $ (8,659) $ (11,435) $ (9,372) $ (8,903) $ (7,369) $ (6,048) $ (3,518) $ (4,911) $ (3,468) $ (3,890) $ 409 $ (5,255) $ (4,007) $ 924 $ (631) Non-GAAP adjustments: Depreciation and amortization 1,699 1,567 1,605 1,775 1,910 1,840 1,863 2,103 2,060 2,140 2,086 2,095 2,270 1,881 2,068 Stock-based compensation 1,723 1,877 1,957 2,235 1,830 1,945 1,720 1,994 2,414 2,519 2,716 3,129 3,854 3,720 4,640 Interest expense 1,092 1,116 1,175 1,139 1,155 1,235 1,198 1,199 1,197 961 869 882 888 865 836 Interest income and other 28 (95) (146) (2) 49 (119) (28) 45 33 (12) (54) (118) (90) (118) (164) Provision for (benefit from) income taxes 12 13 33 18 (20) 50 13 28 42 (2) (14) 49 50 43 126 Extinguishment of debt — — — — — — — — — 1,026 — — — — — Reversal of accrued federal fees — — — — — — — — — — (3,114) — — — — Legal settlement — — — — — — — — — — — 1,700 — — — Legal and indemnification fees related to settlement — — — — — — — — — — — 135 — — — Acquisition-related transaction costs and one- time integration costs — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Loss on early extinguishment of debt — — — — — — — — — — — — — — — Contingent consideration expense — — — — — — — — — — — — — — — Change in fair value of convertible preferred and common stock warrant liabilities — — — — — — — — — — — — — — — Reversal of contingent sales tax liability (G&A) (2,766) — — — — — — — — — — — — — — Reversal of interest and penalties on accrued federal fees (G&A) — — — — — — — — — — — — — (2,133) — Accrued FCC charge (G&A) — 2,000 — — — — — — — — — — — — — Out of period adj. for accrued federal fees (COR) — — 235 — — — — — — — — — — — — Out of period adj. for sales tax liability (G&A) — — 183 575 190 — — — — — — — — — — Adjusted EBITDA $ (6,871) $ (4,957) $ (4,330) $ (3,163) $ (2,255) $ (1,097) $ 1,248 $ 458 $ 2,278 $ 2,742 $ 2,898 $ 2,617 $ 2,965 $ 5,182 $ 6,875 % adjusted EBITDA margin (27.8)% (19.2)% (15.3)% (10.4)% (7.4)% (3.4)% 3.5 % 1.2 % 5.9 % 6.7 % 6.6 % 5.6 % 6.2 % 10.3 % 12.4 %

©Five9, Inc. All rights reserved. | 25 GAAP Net Inc. (Loss) to Adj. EBITDA Reconciliation Q1’18 – Q4’21 Quarter Ended Q1'18 Q2'18 Q3'18 Q4'18 Q1'19 Q2'19 Q3'19 Q4'19 Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 GAAP net income (loss) $ (607) $ (2,042) $ (1,305) $ 3,733 $ (1,924) $ (1,860) $ (1,604) $ 836 $ (7,437) $ (16,052) $ (11,431) $ (7,210) $ (12,332) $ (16,530) $ (20,537) $ (3,601) Non-GAAP adjustments: Depreciation and amortization 2,320 2,449 2,667 2,838 3,192 3,361 3,497 4,324 4,970 6,243 6,537 7,337 8,763 9,651 9,780 10,538 Stock-based compensation 5,325 6,797 8,869 7,493 8,686 10,436 11,075 11,868 13,794 16,791 17,286 16,876 20,908 24,901 27,395 35,601 Interest expense 810 2,378 3,595 3,462 3,396 3,406 3,486 3,506 3,484 5,734 9,649 9,481 1,938 2,118 1,947 2,024 Interest income and other (398) (206) (1,352) (1,359) (1,745) (1,490) (1,460) (1,384) (1,072) (830) (631) (501) (175) 353 (213) 43 Provision for (benefit from) income taxes 45 64 41 150 (49) 29 50 74 69 (2,876) 346 8 (517) (135) (188) (10,445) Extinguishment of debt — — — — — — — — — — — — — — — — Reversal of accrued federal fees — — — — — — — — — — — — — — — — Legal settlement — — — — — 420 — — — — — — — — — — Legal and indemnification fees related to settlement — 241 258 93 292 64 — — — — — — — — — — Acquisition-related transaction costs and one-time integration costs — — — — — — — 338 329 1,637 2,030 2,339 1,094 973 9,158 2,351 Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — 1,817 — — — — — — Loss on early extinguishment of debt — — — — — — — — — 5,795 282 887 — — — — Contingent consideration expense — — — — — — — — — — — — 2,500 2,700 60 380 Refund for prior year overpayment of USF fees — — — — — — — — — — — — — — — — Change in fair value of convertible preferred and common stock warrant liabilities — — — — — — — — — — — — — — — — Reversal of contingent sales tax liability (G&A) — — — — — — — — — — — — — — — — Reversal of interest and penalties on accrued federal fees (G&A) — — — — — — — — — — — — — — — — Accrued FCC charge (G&A) — — — — — — — — — — — — — — — — Out of period adj. for accrued federal fees (COR) — — — — — — — — — — — — — — — — Out of period adj. for sales tax liability (G&A) — — — — — — — — — — — — — — — — Adjusted EBITDA $ 7,495 $ 9,681 $ 12,773 $ 16,410 $ 11,848 $ 14,366 $ 15,044 $ 19,562 $ 14,137 $ 18,259 $ 24,068 $ 29,217 $ 22,179 $ 24,031 $ 27,402 $ 36,891 % adjusted EBITDA margin 12.7 % 15.8 % 19.6 % 22.7 % 15.9 % 18.6 % 18.0 % 21.2 % 14.9 % 18.3 % 21.5 % 22.8 % 16.1 % 16.7 % 17.8 % 21.3 %

©Five9, Inc. All rights reserved. | 26 GAAP Net Inc. (Loss) to Adj. EBITDA Reconciliation Q1’22 – Q2’25 Quarter Ended Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 GAAP net income (loss) $ (34,120) $ (23,670) $ (23,207) $ (13,653) $ (27,248) $ (21,739) $ (20,419) $ (12,358) $ (7,077) $ (12,816) $ (4,479) $ 11,577 $ 576 $ 1,154 Non-GAAP adjustments: Depreciation and amortization 10,795 11,640 11,215 11,021 11,347 11,724 12,482 12,962 12,183 12,938 13,144 14,640 14,490 14,649 Stock-based compensation 39,394 44,786 44,503 43,824 50,743 53,367 52,611 49,571 44,684 43,632 39,556 38,443 39,245 41,859 Interest expense 1,870 1,857 1,879 1,887 1,845 1,866 1,972 1,963 2,567 3,906 4,068 4,271 4,115 3,820 Interest income and other (845) (280) (982) (2,706) (4,121) (6,123) (8,233) (8,322) (10,559) (13,800) (11,144) (11,242) (10,303) (7,917) Provision for (benefit from) income taxes 2,256 332 579 1,221 527 753 942 119 989 3,345 (3,868) (426) 184 1,382 Extinguishment of debt — — — — — — — — (6,615) — — — — — Acquisition-related transaction costs and one-time integration costs 1,638 1,714 1,944 1,605 1,455 877 778 3,670 932 4,089 4,486 2,797 982 1,489 Exit costs related to closure and relocation of Russian operations 3,227 214 774 2,975 596 815 659 243 25 32 21 — — — Lease amortization for finance leases — — — — — — 492 449 457 455 951 1,994 2,008 2,311 Costs related to reduction in force plan — — — — — — — — — — 9,625 — — 7,766 Impairment charge related to closure of operating lease facilities — — — — — — — — — — — 2,202 — 95 One-time expenses related to strategic consulting services for operational review — — — — — — — — — — — — 1,265 — Other cost reduction and productivity initiatives — — — — — — — — — — — — — 974 Legal fees related to the securities class action — — — — — — — — — — — — 141 368 Contingent consideration expense 260 — — — — — — — — — — — — — Refund for prior year overpayment of USF fees — (3,511) — — — — — — — — — — — — Adjusted EBITDA $ 24,475 $ 33,082 $ 36,705 $ 46,174 $ 35,144 $ 41,540 $ 41,284 $ 48,297 $ 37,586 $ 41,781 $ 52,360 $ 64,256 $ 52,703 $ 67,950 % adjusted EBITDA margin 13.4 % 17.5 % 18.5 % 22.2 % 16.1 % 18.6 % 17.9 % 20.2 % 15.2 % 16.6 % 19.8 % 23.1 % 18.8 % 24.0 %

©Five9, Inc. All rights reserved. | 27 GAAP Net Loss to Adjusted EBITDA Reconciliation 2014 – 2019 Year Ended 2014 2015 2016 2017 2018 2019 GAAP net income (loss) $ (37,786) $ (25,838) $ (11,860) $ (8,969) $ (221) $ (4,552) Non-GAAP adjustments: Depreciation and amortization 6,463 7,388 8,390 8,314 10,274 14,374 Stock-based compensation 6,753 7,730 9,643 15,343 28,484 42,065 Interest expense 4,161 4,727 4,226 3,471 10,245 13,794 Interest income and other (245) (100) 13 (490) (3,315) (6,079) Provision for (benefit from) income taxes 85 61 54 268 300 104 Extinguishment of debt — — 1,026 — — — Reversal of accrued federal fees — — (3,114) — — — Legal settlement — — — 1,700 — 420 Legal and indemnification fees related to settlement — — — 135 592 356 Acquisition-related transaction costs and one-time integration costs — — — — — 338 Change in fair value of convertible preferred and common stock warrant liabilities (1,745) — — — — — Refund for prior year overpayment of USF fees — — — — — — Reversal of contingent sales tax liability (G&A) (2,766) — — — — — Reversal of interest and penalties on accrued federal fees (G&A) — — — (2,133) — — Accrued FCC charge (G&A) 2,000 — — — — — Out of period adj. for accrued federal fees (COR) 235 — — — — — Out of period adj. for sales tax liability (G&A) 183 765 — — — — Adjusted EBITDA $ (22,662) $ (5,267) $ 8,378 $ 17,639 $ 46,359 $ 60,820 % adjusted EBITDA margin (22.0) % (4.1)% 5.2 % 8.8 % 18.0 % 18.5 % Note: Historical results prior to 2018 based on ASC 605

©Five9, Inc. All rights reserved. | 28 GAAP Net Loss to Adjusted EBITDA Reconciliation 2020 – 2024 Year Ended 2020 2021 2022 2023 2024 GAAP net income (loss) $ (42,130) $ (53,000) $ (94,650) $ (81,764) $ (12,795) Non-GAAP adjustments: Depreciation and amortization 25,087 38,732 44,671 48,515 52,905 Stock-based compensation 64,747 108,805 172,507 206,292 166,315 Interest expense 28,348 8,027 7,493 7,646 14,812 Interest income and other (3,034) 8 (4,813) (26,799) (46,745) Provision for (benefit from) income taxes (2,453) (11,285) 4,388 2,341 40 Acquisition-related transaction costs and one-time integration costs 6,335 13,576 6,901 6,780 12,303 Exit costs related to closure and relocation of Russian operations — — 7,190 2,313 78 Costs related to reduction in force plan — — — — 9,625 Impairment charge related to closure of operating lease facilities — — — — 2,202 COVID-19 relief bonus for employees 1,817 — — — — (Gain) loss on early extinguishment of debt 6,964 — — — (6,615) Contingent consideration expense — 5,640 260 — — Refund for prior year overpayment of USF fees — — (3,511) — — Lease amortization for finance leases — — — 941 3,857 Adjusted EBITDA $ 85,681 $ 110,503 $ 140,436 $ 166,265 $ 195,982 % adjusted EBITDA margin 19.7 % 18.1 % 18.0 % 18.3 % 18.8 %

©Five9, Inc. All rights reserved. | 29 GAAP to Non-GAAP COR and OpEx Reconciliation Q2’14 – Q4’17 Quarter Ended Q2'14 Q3'14 Q4'14 Q1'15 Q2'15 Q3'15 Q4'15 Q1'16 Q2'16 Q3'16 Q4'16 Q1'17 Q2'17 Q3'17 Q4'17 GAAP COR $ 13,469 $ 13,504 $ 14,540 $ 14,778 $ 14,270 $ 14,812 $ 15,635 $ 16,610 $ 16,764 $ 17,790 $ 15,770 $ 19,971 $ 20,273 $ 20,497 $ 22,363 % of revenue 54.6 % 52.2 % 51.4 % 48.8 % 47.1 % 45.9 % 43.4 % 43.7 % 43.1 % 43.4 % 35.7 % 42.5 % 42.5 % 40.9 % 40.4 % Depreciation & amortization (1,373) (1,272) (1,291) (1,439) (1,558) (1,470) (1,483) (1,680) (1,616) (1,668) (1,608) (1,576) (1,716) (1,397) (1,611) Stock-based compensation (121) (158) (176) (188) (218) (233) (227) (265) (329) (357) (424) (434) (575) (599) (594) Acquisition-related transaction costs and one-time integration costs — — — — — — — — — — — — — — — Reversal of accrued federal fees — — — — — — — — — — 3,114 — — — — Out of period adj. for accrued federal fees — — (235) — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Non-GAAP COR $ 11,975 $ 12,074 $ 12,838 $ 13,151 $ 12,494 $ 13,109 $ 13,925 $ 14,665 $ 14,819 $ 15,765 $ 16,852 $ 17,961 $ 17,982 $ 18,501 $ 20,158 % of revenue 48.5 % 46.7 % 45.4 % 43.4 % 41.3 % 40.6 % 38.6 % 38.6 % 38.1 % 38.5 % 38.1 % 38.2 % 37.7 % 36.9 % 36.4 % GAAP R&D $ 5,554 $ 5,503 $ 5,828 $ 6,038 $ 5,568 $ 5,473 $ 5,580 $ 5,802 $ 5,799 $ 6,041 $ 6,236 $ 6,847 $ 6,836 $ 6,689 $ 6,748 % of revenue 22.5 % 21.3 % 20.6 % 19.9 % 18.4 % 17.0 % 15.5 % 15.3 % 14.9 % 14.7 % 14.1 % 14.6 % 14.3 % 13.4 % 12.2 % Depreciation & amortization (50) (58) (75) (87) (102) (126) (140) (148) (161) (204) (224) (206) (237) (182) (170) Stock-based compensation (471) (583) (527) (574) (340) (475) (401) (435) (528) (547) (549) (637) (801) (797) (807) Acquisition-related transaction costs and one-time integration costs — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Non-GAAP R&D $ 5,033 $ 4,862 $ 5,226 $ 5,377 $ 5,126 $ 4,872 $ 5,039 $ 5,219 $ 5,110 $ 5,290 $ 5,463 $ 6,004 $ 5,798 $ 5,710 $ 5,771 % of revenue 20.4 % 18.8 % 18.5 % 17.8 % 16.9 % 15.1 % 14.0 % 13.7 % 13.1 % 12.9 % 12.4 % 12.8 % 12.1 % 11.4 % 10.4 % Note: Historical results prior to 2018 based on ASC 605

©Five9, Inc. All rights reserved. | 30 GAAP to Non-GAAP OpEx Reconciliation Q2’14 – Q4’17 Note: Historical results prior to 2018 based on ASC 605 Quarter Ended Q2'14 Q3'14 Q4'14 Q1'15 Q2'15 Q3'15 Q4'15 Q1'16 Q2'16 Q3'16 Q4'16 Q1'17 Q2'17 Q3'17 Q4'17 GAAP S&M $ 9,674 $ 9,296 $ 9,453 $ 9,931 $ 10,594 $ 10,797 $ 10,720 $ 12,706 $ 12,637 $ 12,925 $ 14,480 $ 15,778 $ 16,932 $ 16,502 $ 17,358 % of revenue 39.2 % 35.9 % 33.4 % 32.8 % 35.0 % 33.4 % 29.8 % 33.4 % 32.5 % 31.5 % 32.8 % 33.6 % 35.5 % 33.0 % 31.3 % Depreciation & amortization (48) (50) (50) (49) (51) (52) (54) (53) (54) (56) (58) (30) (30) (30) (30) Stock-based compensation (368) (361) (455) (524) (458) (448) (370) (434) (544) (626) (759) (928) (1,224) (1,084) (1,128) Acquisition-related transaction costs and one-time integration costs — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Non-GAAP S&M 9,258 8,885 8,948 9,358 10,085 10,297 10,296 12,219 12,039 12,243 13,663 14,820 15,678 15,388 16,200 % of revenue 37.5 % 34.3 % 31.6 % 30.9 % 33.3 % 31.9 % 28.6 % 32.1 % 31.0 % 29.9 % 30.9 % 31.5 % 32.8 % 30.7 % 29.2 %

©Five9, Inc. All rights reserved. | 31 GAAP to Non-GAAP OpEx Reconciliation Q2’14 – Q4’17 Note: Historical results prior to 2018 based on ASC 605 Quarter Ended Q2'14 Q3'14 Q4'14 Q1'15 Q2'15 Q3'15 Q4'15 Q1'16 Q2'16 Q3'16 Q4'16 Q1'17 Q2'17 Q3'17 Q4'17 GAAP G&A $ 3,515 $ 7,967 $ 6,763 $ 7,275 $ 6,027 $ 6,087 $ 6,433 $ 6,536 $ 5,882 $ 6,143 $ 6,511 $ 8,860 $ 6,845 $ 4,679 $ 8,767 % of revenue 14.2 % 30.8 % 23.9 % 24.0 % 19.9 % 18.9 % 17.9 % 17.2 % 15.1 % 15.0 % 14.7 % 18.8 % 14.3 % 9.3 % 15.8 % Depreciation & amortization (228) (187) (189) (200) (199) (192) (186) (222) (229) (212) (196) (283) (287) (272) (257) Stock-based compensation (763) (775) (799) (949) (814) (789) (722) (860) (1,013) (989) (984) (1,130) (1,254) (1,240) (2,111) Legal settlement — — — — — — — — — — — (1,700) — — — Legal and indemnification fees related to settlement — — — — — — — — — — — (135) — — — Acquisition and related transaction costs and one-time integration costs — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — — — — — — — Contingent consideration expense — — — — — — — — — — — — — — — Reversal of contingent sales tax liability 2,766 — — — — — — — — — — — — — — Reversal of interest & penalties on accrued fed. fees — — — — — — — — — — — — — 2,133 — Accrued FCC charge — (2,000) — — — — — — — — — — — — — Out of period adj. for sales tax liability — — (183) (575) (190) — — — — — — — — — — Non-GAAP G&A 5,290 5,005 5,592 5,551 4,824 5,106 5,525 5,454 4,640 4,942 5,331 5,612 5,304 5,300 6,399 % of revenue 21.4 % 19.3 % 19.8 % 18.3 % 15.9 % 15.8 % 15.3 % 14.3 % 11.9 % 12.1 % 12.1 % 11.9 % 11.1 % 10.6 % 11.5 %

©Five9, Inc. All rights reserved. | 32 GAAP to Non-GAAP COR and OpEx Reconciliation Q1’18 – Q4’21 Quarter Ended Q1'18 Q2'18 Q3'18 Q4'18 Q1'19 Q2'19 Q3'19 Q4'19 Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 GAAP COR $ 24,702 $ 24,814 $ 26,179 $ 28,339 $ 30,851 $ 31,248 $ 34,472 $ 37,940 $ 40,037 $ 42,453 $ 46,561 $ 51,233 $ 59,803 $ 64,395 $ 67,137 $ 79,764 % of revenue 41.9 % 40.6 % 40.1 % 39.2 % 41.4 % 40.4 % 41.2 % 41.1 % 42.1 % 42.5 % 41.5 % 40.1 % 43.4 % 44.8 % 43.5 % 45.9 % Depreciation & amortization (1,794) (1,864) (2,021) (2,129) (2,366) (2,504) (2,602) (3,384) (3,940) (5,120) (5,171) (5,948) (7,087) (7,825) (7,658) (8,301) Stock-based compensation (678) (853) (860) (942) (1,229) (1,658) (1,702) (1,745) (1,989) (2,499) (2,603) (2,331) (3,105) (3,781) (3,994) (6,854) Acquisition-related transaction costs and one-time integration costs — — — — — — — — — — — — (30) (2) (37) (43) Reversal of accrued federal fees — — — — — — — — — — — — — — — — Out of period adj. for accrued federal fees — — — — — — — — — — — — — — — — Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — (618) — — — — — — Refund for prior year overpayment of USF fees — — — — — — — — — — — — — — — — Non-GAAP COR $ 22,230 $ 22,097 $ 23,298 $ 25,268 $ 27,256 $ 27,086 $ 30,168 $ 32,811 $ 34,108 $ 34,216 $ 38,787 $ 42,954 $ 49,581 $ 52,787 $ 55,448 $ 64,566 % of revenue 37.7 % 36.2 % 35.7 % 34.9 % 36.6 % 35.0 % 36.0 % 35.6 % 35.9 % 34.3 % 34.6 % 33.6 % 36.0 % 36.7 % 35.9 % 37.2 % GAAP R&D $ 7,772 $ 8,367 $ 9,582 $ 8,451 $ 10,546 $ 10,811 $ 11,665 $ 12,168 $ 15,189 $ 17,208 $ 17,674 $ 18,676 $ 22,121 $ 24,648 $ 29,680 $ 30,448 % of revenue 13.2 % 13.7 % 14.7 % 11.7 % 14.1 % 14.0 % 13.9 % 13.2 % 16.0 % 17.2 % 15.8 % 14.6 % 16.0 % 17.1 % 19.2 % 17.5 % Depreciation & amortization (194) (233) (278) (331) (440) (450) (450) (461) (465) (497) (512) (488) (596) (729) (1,004) (948) Stock-based compensation (877) (1,064) (2,352) (1,010) (1,470) (1,907) (2,022) (2,259) (2,806) (3,684) (3,876) (3,675) (4,763) (6,152) (9,101) (9,163) Acquisition-related transaction costs and one-time integration costs — — — — — — — — — (248) (439) (332) (337) (666) (660) (462) Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — (365) — — — — — — Non-GAAP R&D $ 6,701 $ 7,070 $ 6,952 $ 7,110 $ 8,636 $ 8,454 $ 9,193 $ 9,448 $ 11,918 $ 12,414 $ 12,847 $ 14,181 $ 16,425 $ 17,101 $ 18,915 $ 19,875 % of revenue 11.4 % 11.6 % 10.6 % 9.8 % 11.6 % 10.9 % 11.0 % 10.2 % 12.5 % 12.4 % 11.5 % 11.1 % 11.9 % 11.9 % 12.3 % 11.4 %

©Five9, Inc. All rights reserved. | 33 GAAP to Non-GAAP COR and OpEx Reconciliation Q1’22 – Q2’25 Quarter Ended Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 GAAP COR $ 88,867 $ 88,229 $ 94,111 $ 96,294 $ 104,756 $ 104,361 $ 111,080 $ 112,493 $ 114,530 $ 118,414 $ 121,933 $ 122,663 $ 125,973 $ 127,865 % of revenue 48.6 % 46.6 % 47.4 % 46.2 % 48.0 % 46.8 % 48.3 % 47.1 % 46.4 % 47.0 % 46.2 % 44.0 % 45.0 % 45.1 % Depreciation & amortization (8,500) (8,747) (8,904) (8,803) (8,907) (9,269) (10,075) (10,308) (9,613) (10,421) (10,414) (12,087) (11,883) (12,161) Stock-based compensation (7,793) (8,538) (8,329) (8,638) (9,333) (9,888) (9,856) (9,182) (7,603) (7,789) (7,512) (6,921) (7,184) (7,296) Acquisition-related transaction costs and one-time integration costs (48) (80) (187) (86) (34) — — (63) (53) (72) (94) (40) — — Exit costs related to closure and relocation of Russian operations (380) (3) (96) (219) (23) (51) (18) (12) — — — — — — Lease amortization for finance leases — — — — — — (492) (449) (457) (455) (895) (1,802) (1,816) (2,119) Costs related to reduction in force plan — — — — — — — — — — (2,115) — — (1,565) Refund for prior year overpayment of USF fees — 3,511 — — — — — — — — — — — — Non-GAAP COR $ 72,146 $ 74,372 $ 76,595 $ 78,548 $ 86,459 $ 85,153 $ 90,639 $ 92,479 $ 96,804 $ 99,677 $ 100,903 $ 101,813 $ 105,090 $ 104,724 % of revenue 39.5 % 39.3 % 38.6 % 37.7 % 39.6 % 38.2 % 39.4 % 38.7 % 39.2 % 39.5 % 38.2 % 36.5 % 37.6 % 37.0 % GAAP R&D $ 35,824 $ 34,992 $ 34,113 $ 36,865 $ 38,108 $ 39,210 $ 40,391 $ 38,873 $ 41,518 $ 40,717 $ 42,482 $ 41,480 $ 41,100 $ 39,912 % of revenue 19.6 % 18.5 % 17.2 % 17.7 % 17.4 % 17.6 % 17.6 % 16.3 % 16.8 % 16.2 % 16.1 % 14.9 % 14.7 % 14.1 % Depreciation & amortization (825) (804) (768) (768) (872) (868) (831) (1,012) (890) (741) (721) (620) (680) (799) Stock-based compensation (10,145) (11,818) (10,603) (11,799) (12,382) (13,013) (12,980) (12,055) (10,930) (9,827) (8,244) (8,259) (8,690) (8,829) Acquisition-related transaction costs and one-time integration costs (656) (1,307) (1,654) (1,449) (1,423) — — (12) (323) (488) (412) (501) (466) (742) Exit costs related to closure and relocation of Russian operations (2,629) (59) (557) (2,615) (475) (542) (503) (197) (8) (28) (18) — — — Lease amortization for finance leases — — — — — — — — — — — (192) (192) (192) Costs related to reduction in force plan — — — — — — — — — — (1,942) — — (1,931) COVID-19 relief bonus for — — — — — — — — — — — — — — Non-GAAP R&D $ 21,569 $ 21,004 $ 20,531 $ 20,234 $ 22,956 $ 24,787 $ 26,077 $ 25,597 $ 29,367 $ 29,633 $ 31,145 $ 31,908 $ 31,072 $ 27,419 % of revenue 11.8 % 11.1 % 10.4 % 9.7 % 10.5 % 11.1 % 11.3 % 10.7 % 11.9 % 11.8 % 11.8 % 11.5 % 11.1 % 9.7 %

©Five9, Inc. All rights reserved. | 34 GAAP to Non-GAAP OpEx Reconciliation Q1’18 – Q4’21 Quarter Ended Q1'18 Q2'18 Q3'18 Q4'18 Q1'19 Q2'19 Q3'19 Q4'19 Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 GAAP S&M $ 17,478 $ 17,912 $ 17,818 $ 18,793 $ 21,701 $ 23,250 $ 25,014 $ 25,627 $ 30,160 $ 32,231 $ 32,969 $ 37,053 $ 44,799 $ 46,024 $ 49,712 $ 53,394 % of revenue 29.7 % 29.3 % 27.3 % 26.0 % 29.1 % 30.0 % 29.9 % 27.8 % 31.7 % 32.3 % 29.4 % 29.0 % 32.5 % 32.0 % 32.2 % 30.8 % Depreciation & amortization (29) (30) (30) (6) (1) (1) (2) (2) (2) (2) (1) (2) (1) (1) (1) (1) Stock-based compensation (1,362) (1,585) (1,613) (1,747) (2,249) (2,749) (3,017) (3,353) (4,106) (5,265) (5,427) (5,366) (6,771) (8,208) (8,304) (11,987) Acquisition-related transaction costs and one- time integration costs — — — — — — — — — (169) (28) (43) (11) (28) (322) (642) Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — (596) — — — — — — Non-GAAP S&M $ 16,087 $ 16,297 $ 16,175 $ 17,040 $ 19,451 $ 20,500 $ 21,995 $ 22,272 $ 26,052 $ 26,199 $ 27,513 $ 31,642 $ 38,016 $ 37,787 $ 41,085 $ 40,764 % of revenue 27.3 % 26.7 % 24.8 % 23.6 % 26.1 % 26.5 % 26.3 % 24.1 % 27.4 % 26.3 % 24.5 % 24.7 % 27.6 % 26.3 % 26.6 % 23.5 %

©Five9, Inc. All rights reserved. | 35 GAAP to Non-GAAP OpEx Reconciliation Q1’22 – Q2’25 Quarter Ended Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 GAAP S&M $ 64,611 $ 64,098 $ 67,353 $ 65,928 $ 76,314 $ 74,077 $ 73,366 $ 72,956 $ 81,109 $ 78,332 $ 78,615 $ 73,898 $ 82,855 $ 80,668 % of revenue 35.3 % 33.8 % 34.0 % 31.6 % 34.9 % 33.2 % 31.9 % 30.5 % 32.8 % 31.1 % 29.8 % 26.5 % 29.6 % 28.5 % Depreciation & amortization (1) (1) (1) (1) (1) (1) (36) (27) (27) (26) (32) (38) (36) (27) Stock-based compensation (13,424) (14,963) (15,761) (15,152) (17,045) (17,391) (16,404) (15,389) (14,020) (13,824) (12,490) (10,880) (11,574) (13,355) Acquisition-related transaction costs and one- time integration costs (46) (23) — — — — — — — — — — — — Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — Costs related to reduction in force plan — — — — — — — — — — (4,424) — — (3,319) COVID-19 relief bonus for employees — — — — — — — — — — — — — — Non-GAAP S&M $ 51,140 $ 49,111 $ 51,591 $ 50,775 $ 59,268 $ 56,685 $ 56,926 $ 57,540 $ 67,062 $ 64,482 $ 61,669 $ 62,980 $ 71,245 $ 63,967 % of revenue 28.0 % 25.9 % 26.0 % 24.4 % 27.1 % 25.4 % 24.7 % 24.1 % 27.1 % 25.6 % 23.3 % 22.6 % 25.5 % 22.6 %

©Five9, Inc. All rights reserved. | 36 GAAP to Non-GAAP OpEx Reconciliation Q1’18 – Q4’21 Quarter Ended Q1'18 Q2'18 Q3'18 Q4'18 Q1'19 Q2'19 Q3'19 Q4'19 Q1'20 Q2'20 Q3'20 Q4'20 Q1'21 Q2'21 Q3'21 Q4'21 GAAP G&A $ 9,103 $ 9,833 $ 10,746 $ 10,766 $ 11,762 $ 12,042 $ 12,146 $ 13,496 $ 14,658 $ 16,129 $ 16,724 $ 18,258 $ 22,245 $ 22,909 $ 26,790 $ 21,972 % of revenue 15.5 % 16.1 % 16.5 % 14.9 % 15.8 % 15.6 % 14.5 % 14.6 % 15.4 % 16.2 % 14.9 % 14.3 % 16.1 % 15.9 % 17.4 % 12.7 % Depreciation & amortization (303) (322) (338) (372) (385) (406) (443) (477) (563) (624) (853) (899) (1,079) (1,096) (1,117) (1,288) Stock-based compensation (2,408) (3,295) (4,044) (3,794) (3,738) (4,122) (4,334) (4,511) (4,893) (5,343) (5,380) (5,504) (6,269) (6,760) (5,996) (7,597) Legal settlement — — — — — (420) — — — — — — — — — — Legal and indemnification fees related to settlement — (241) (258) (93) (292) (64) — — — — — — — — — — Acquisition and related transaction costs and one-time integration costs — — — — — — — (338) (329) (1,220) (1,563) (1,964) (716) (278) (8,139) (1,204) Exit costs related to closure and relocation of Russian operations — — — — — — — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — — — — (238) — — — — — — Contingent consideration expense — — — — — — — — — — — — (2,500) (2,700) (60) (380) Reversal of contingent sales tax liability — — — — — — — — — — — — — — — — Reversal of interest & penalties on accrued fed. fees — — — — — — — — — — — — — — — — Accrued FCC charge — — — — — — — — — — — — — — — — Out of period adj. for sales tax liability — — — — — — — — — — — — — — — — Non-GAAP G&A $ 6,392 $ 5,975 $ 6,106 $ 6,507 $ 7,347 $ 7,030 $ 7,369 $ 8,170 $ 8,873 $ 8,704 $ 8,928 $ 9,891 $ 11,681 $ 12,075 $ 11,478 $ 11,503 % of revenue 10.9 % 9.8 % 9.4 % 9.0 % 9.9 % 9.1 % 8.8 % 8.9 % 9.3 % 8.7 % 8.0 % 7.7 % 8.5 % 8.4 % 7.4 % 6.6 %

©Five9, Inc. All rights reserved. | 37 GAAP to Non-GAAP OpEx Reconciliation Q1’22 – Q2’25 Quarter Ended Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 GAAP G&A $ 24,314 $ 23,824 $ 24,496 $ 22,509 $ 28,258 $ 30,477 $ 31,006 $ 33,338 $ 30,548 $ 33,988 $ 36,575 $ 36,439 $ 35,205 $ 36,385 % of revenue 13.3 % 12.6 % 12.4 % 10.8 % 12.9 % 13.7 % 13.5 % 13.9 % 12.4 % 13.5 % 13.8 % 13.1 % 12.6 % 12.8 % Depreciation & amortization (1,469) (2,088) (1,542) (1,449) (1,567) (1,586) (1,540) (1,615) (1,653) (1,750) (1,977) (1,895) (1,891) (1,662) Stock-based compensation (8,032) (9,467) (9,810) (8,235) (11,983) (13,075) (13,371) (12,945) (12,131) (12,192) (11,310) (12,383) (11,797) (12,379) Acquisition and related transaction costs and one-time integration costs (888) (304) (103) (70) 2 (877) (778) (3,595) (556) (3,529) (3,980) (2,256) (516) (746) Exit costs related to closure and relocation of Russian operations (218) (152) (121) (141) (98) (222) (138) (34) (17) (4) (3) — — — Lease amortization for finance leases — — — — — — — — — — (56) — — — Costs related to reduction in force plan — — — — — — — — — — (1,144) — — (952) Impairment charge related to closure of operating lease facilities — — — — — — — — — — — (2,202) — — Office closure lease termination costs — — — — — — — — — — — — — (95) One-time expenses related to strategic consulting services for operational review — — — — — — — — — — — — (1,265) — Other cost reduction and productivity initiatives — — — — — — — — — — — — — (974) Legal fees related to the securities class action — — — — — — — — — — — — (141) (368) Contingent consideration expense (260) — — — — — — — — — — — — — Non-GAAP G&A $ 13,447 $ 11,813 $ 12,920 $ 12,614 $ 14,612 $ 14,717 $ 15,179 $ 15,149 $ 16,191 $ 16,513 $ 18,105 $ 17,703 $ 19,595 $ 19,209 % of revenue 7.4 % 6.2 % 6.5 % 6.1 % 6.7 % 6.6 % 6.6 % 6.3 % 6.6 % 6.6 % 6.9 % 6.4 % 7.0 % 6.8 %

©Five9, Inc. All rights reserved. | 38 GAAP to Non-GAAP COR Reconciliation 2014 – 2024 Year Ended 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 GAAP COR $ 54,661 $ 59,495 $ 66,934 $ 83,104 $ 104,034 $ 134,511 $ 180,284 $ 271,099 $ 367,501 $ 432,690 $ 477,540 % of revenue 53.0 % 46.2 % 41.3 % 41.5 % 40.4 % 41.0 % 41.5 % 44.5 % 47.2 % 47.5 % 45.8 % Depreciation & amortization (5,138) (5,950) (6,573) (6,300) (7,808) (10,856) (20,179) (30,870) (34,955) (38,559) (42,535) Stock-based compensation (542) (866) (1,375) (2,202) (3,333) (6,334) (9,422) (17,734) (33,297) (38,259) (29,825) Acquisition and related transaction costs and one-time integration costs — — — — — — — (112) (401) (34) (259) Exit costs related to closure and relocation of Russian operations — — — — — — — — (698) (105) — Refund for prior year overpayment of USF fees — — — — — — — — 3,511 — — Lease amortization for finance leases — — — — — — — — — (941) (3,609) Costs related to a reduction in force plan — — — — — — — — — — — Reversal of accrued federal fees — — 3,114 — — — — — — — (2,115) Out of period adj. for accrued federal fees (235) — — — — — — — — — — COVID-19 relief bonus for employees — — — — — — (618) — — — — Non-GAAP COR $ 48,746 $ 52,679 $ 62,100 $ 74,602 $ 92,893 $ 117,321 $ 150,065 $ 222,383 $ 301,661 $ 354,792 $ 399,197 % of revenue 47.3 % 40.9 % 38.3 % 37.3 % 36.1 % 35.8 % 34.5 % 36.5 % 38.7 % 39.0 % 38.3 % Note: Historical results prior to 2018 based on ASC 605

©Five9, Inc. All rights reserved. | 39 GAAP to Non-GAAP OpEx Reconciliation 2014 – 2024 Note: Historical results prior to 2018 based on ASC 605 Year Ended 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 GAAP R&D $ 22,110 $ 22,659 $ 23,878 $ 27,120 $ 34,172 $ 45,190 $ 68,747 $ 106,897 $ 141,794 $ 156,582 $ 166,197 % of revenue 21.4 % 17.6 % 14.7 % 13.5 % 13.3 % 13.8 % 15.8 % 17.5 % 18.2 % 17.2 % 16.0 % Depreciation & amortization (229) (455) (737) (795) (1,036) (1,801) (1,962) (3,277) (3,164) (3,583) (2,972) Stock-based compensation (1,931) (1,790) (2,059) (3,042) (5,303) (7,658) (14,041) (29,179) (44,367) (50,430) (37,260) Acquisition and related transaction costs and one-time integration costs — — — — — — (1,019) (2,125) (5,066) (1,435) (1,724) Exit costs related to closure and relocation of Russian operations — — — — — — — — (5,860) (1,717) (54) Lease amortization for finance leases — — — — — — — — — — (192) Costs related to a reduction in force plan — — — — — — — — — — (1,942) COVID-19 relief bonus for employees — — — — — — (365) — — — — Non-GAAP R&D $ 19,950 $ 20,414 $ 21,082 $ 23,283 $ 27,833 $ 35,731 $ 51,360 $ 72,316 $ 83,337 $ 99,417 $ 122,053 % of revenue 19.3 % 15.8 % 13.0 % 11.6 % 10.8 % 10.9 % 11.8 % 11.9 % 10.7 % 10.9 % 11.7 %

©Five9, Inc. All rights reserved. | 40 GAAP to Non-GAAP OpEx Reconciliation 2014 – 2024 Note: Historical results prior to 2018 based on ASC 605 Year Ended 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 GAAP S&M $ 37,445 $ 42,042 $ 52,748 $ 66,570 $ 72,001 $ 95,592 $ 132,413 $ 193,929 $ 261,990 $ 296,713 $ 311,954 % of revenue 36.3 % 32.6 % 32.5 % 33.2 % 27.9 % 29.1 % 30.4 % 31.8 % 33.6 % 32.6 % 29.9 % Depreciation & amortization (196) (206) (221) (120) (95) (6) (7) (4) (4) (65) (123) Stock-based compensation (1,510) (1,800) (2,363) (4,364) (6,307) (11,368) (20,164) (35,270) (59,300) (66,229) (51,214) Acquisition and related transaction costs and one-time integration costs — — — — — — (240) (1,003) (69) — — Costs related to a reduction in force plan — — — — — — — — — — (4,424) COVID-19 relief bonus for employees — — — — — — (596) — — — — Non-GAAP S&M $ 35,739 $ 40,036 $ 50,164 $ 62,086 $ 65,599 $ 84,218 $ 111,406 $ 157,652 $ 202,617 $ 230,419 $ 256,193 % of revenue 34.7 % 31.1 % 30.9 % 31.0 % 25.5 % 25.7 % 25.6 % 25.9 % 26.0 % 25.3 % 24.6 %

©Five9, Inc. All rights reserved. | 41 GAAP to Non-GAAP OpEx Reconciliation 2014 – 2024 Note: Historical results prior to 2018 based on ASC 605 t Year Ended 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 GAAP G&A $ 24,416 $ 25,822 $ 25,072 $ 29,151 $ 40,448 $ 49,446 $ 65,769 $ 93,916 $ 95,143 $ 123,079 $ 137,550 % of revenue 23.7 % 20.0 % 15.5 % 14.6 % 15.7 % 15.1 % 15.1 % 15.4 % 12.2 % 13.5 % 13.2 % Depreciation & amortization (900) (777) (859) (1,099) (1,335) (1,711) (2,939) (4,581) (6,548) (6,308) (7,275) Stock-based compensation (2,770) (3,274) (3,846) (5,735) (13,541) (16,705) (21,120) (26,622) (35,543) (51,374) (48,016) Legal settlement — — — (1,700) — (420) — — — — — Legal and indemnification fees related to settlement — — — (135) (592) (356) — — — — — Acquisition and related transaction costs and one-time integration costs — — — — — (338) (5,076) (10,336) (1,365) (5,248) (10,320) Exit costs related to closure and relocation of Russian operations — — — — — — — — (632) (492) (24) Lease amortization for finance leases — — — — — — — — — — (56) Costs related to a reduction in force plan — — — — — — — — — — (1,144) Impairment charge related to closure of operating lease facilities — — — — — — — — — — (2,202) COVID-19 relief bonus for employees — — — — — — (238) — — — — Contingent consideration expense — — — — — — — (5,640) (260) — — Reversal of contingent sales tax liability 2,766 — — — — — — — — — — Reversal of interest & penalties on accrued federal fees — — — 2,133 — — — — — — — Accrued FCC charge (2,000) — — — — — — — — — — Out of period adj. for sales tax liability (183) (765) — — — — — — — — — Non-GAAP G&A $ 21,329 $ 21,006 $ 20,367 $ 22,615 $ 24,980 $ 29,916 $ 36,396 $ 46,737 $ 50,795 $ 59,657 $ 68,513 % of revenue 20.7 % 16.3 % 12.6 % 11.3 % 9.7 % 9.1 % 8.4 % 7.7 % 6.5 % 6.6 % 6.6 %

©Five9, Inc. All rights reserved. | 42 GAAP to Non-GAAP Net Income (Loss) Reconciliation (1) Non-GAAP adjustments do not have a material impact on our worldwide income tax provision due to the tax treatment of non-GAAP adjustments reported, and our domestic valuation allowance position. Three Months Ended Six Months Ended June 30, 2025 June 30, 2024 June 30, 2025 June 30, 2024 GAAP net income (loss) $ 1,154 $ (12,816) $ 1,730 $ (19,893) Non-GAAP adjustments: Stock-based compensation 41,859 43,632 81,104 88,316 Intangibles amortization 3,464 2,648 7,564 5,296 Amortization of discount and issuance costs on convertible senior notes 1,273 1,435 2,680 2,509 Gain on early extinguishment of debt — — — (6,615) Acquisition and related transaction costs and one-time integration costs 1,489 4,089 2,470 5,020 Exit costs related to closure and relocation of Russian operations (169) (114) (545) (20) Costs related to reduction in force plan 7,766 — 7,766 — One-time expenses related to strategic consulting services for operational review — — 1,265 — Other cost reduction and productivity initiatives 974 — 974 — Legal fees related to the securities class action 368 — 509 — Office closure lease termination costs 95 — 95 — Income tax expense effects(1) — — — — Non-GAAP net income $ 58,273 $ 38,874 $ 105,612 $ 74,613 GAAP net income (loss) per share: Basic $ 0.02 $ (0.17) $ 0.02 $ (0.27) Diluted $ 0.01 $ (0.17) $ 0.02 $ (0.27) Non-GAAP net income per share: Basic $ 0.76 $ 0.52 $ 1.38 $ 1.01 Diluted $ 0.76 $ 0.52 $ 1.37 $ 1.00 Shares used in computing GAAP net income (loss) per share: Basic 76,654 74,203 76,303 73,845 Diluted 88,523 74,203 88,964 73,845 Shares used in computing non-GAAP net income per share: Basic 76,654 74,203 76,303 73,845 Diluted 76,919 74,647 76,836 74,415

©Five9, Inc. All rights reserved. | 43 Capital Expenditure and Free Cash Flow Q1'22 - Q4'23 $ in Thousands Q1'22 Q2'22 Q3'22 Q4'22 12 mo ended 12/31/2022 Q1'23 Q2'23 Q3'23 Q4'23 12 mo ended 12/31/2023 Net cash provided by operating activities $ 28,724 $ (3,125) $ 30,526 $ 32,740 $ 88,865 $ 33,412 $ 21,852 $ 37,030 $ 36,544 $ 128,838 (Refer to cash flows from operating activities in cash flow stmt) Capital expenditure Purchases of property and equipment 12,398 22,076 11,554 6,244 52,272 9,928 6,714 3,299 11,293 31,234 (Refer to cash flows from investing activities in cash flow stmt) Capitalization of software development costs 569 823 1,028 1,479 3,899 1,806 1,759 2,255 3,717 9,537 Equipment purchased and unpaid at period-end: Beginning balance 13,871 22,365 16,141 13,372 13,871 12,332 8,310 5,849 11,419 12,332 Ending balance 22,365 16,141 13,372 12,332 12,332 8,310 5,849 11,419 11,243 11,243 (Refer to non-cash investing and financing activities in cash flow stmt) Change in equipment purchased and unpaid during period 8,494 (6,224) (2,769) (1,040) (1,539) (4,022) (2,461) 5,570 (176) (1,089) Total capital expenditure $ 21,461 $ 16,675 $ 9,813 $ 6,683 $ 54,632 $ 7,712 $ 6,012 $ 11,124 $ 14,834 $ 39,682 Free cash flow $ 15,757 $ (26,024) $ 17,944 $ 25,017 $ 32,694 $ 21,678 $ 13,379 $ 31,476 $ 21,534 $ 88,067 (operating cash flow less capex paid in cash and capitalized software) Note 1: Revised original cash flow presentation to include restricted cash, which resulted in the following changes in net cash from operating activities from the originally reported disclosures: (1) Q2'22 changed from $(3,103k) to $(3,125k) (2) Q3'22 changed from $30,504k to $30,526k

©Five9, Inc. All rights reserved. | 44 Capital Expenditure and Free Cash Flow Q1’24 – Q2’25 $ in Thousands Q1'24 Q2'24 Q3'24 Q4'24 12 mo ended 12/31/2024 Q1'25 Q2'25 Net cash provided by operating activities $ 32,353 $ 19,878 $ 41,122 $ 49,815 $ 143,168 $ 48,384 $ 35,061 (Refer to cash flows from operating activities in cash flow stmt) Capital expenditure Purchases of property and equipment 11,951 6,771 14,375 9,291 42,388 4,724 3,494 (Refer to cash flows from investing activities in cash flow stmt) Capitalization of software development costs 3,242 5,018 5,951 8,012 22,223 8,732 9,998 Equipment purchased and unpaid at period-end: Beginning balance 11,243 9,335 16,684 12,944 11,243 11,890 9,330 Ending balance 9,335 16,684 12,944 11,890 11,890 9,330 13,058 (Refer to non-cash investing and financing activities in cash flow stmt) Change in equipment purchased and unpaid during period (1,908) 7,349 (3,740) (1,054) (647) (2,560) 3,728 Total capital expenditure $ 13,285 $ 19,138 $ 16,586 $ 16,249 $ 65,258 $ 10,896 $ 17,220 Free cash flow $ 17,160 $ 8,089 $ 20,796 $ 32,512 $ 78,557 $ 34,928 $ 21,569 (operating cash flow less capex paid in cash and capitalized software)

©Five9, Inc. All rights reserved. | 45 GAAP to Non-GAAP Net Income Reconciliation Guidance(1) (1) Represents guidance discussed on 07/31/2025. Reader shall not construe presentation of this information after 07/31/2025 as an update or reaffirmation of such guidance. (2) Stock-based compensation expense are based on a range of probable significance, assuming market price for our common stock that is approximately consistent with current levels. (3) Acquisition and related transaction costs and one-time integration costs are based on a range of probable significance for completed acquisitions, and no new acquisitions assumed. (4) Non-GAAP adjustments do not have a material impact on our worldwide income tax provision due to the tax treatment of the non-GAAP adjustments reported, and our domestic valuation allowance position. Three Months Ended Twelve Months Ended September 30, 2025 December 31, 2025 Low High Low High GAAP net income $ 5,515 $ 10,077 $ 20,238 $ 26,346 Non-GAAP adjustments: Stock-based compensation(2) 41,509 39,509 162,022 160,022 Intangibles amortization 2,643 2,643 12,849 12,849 Amortization of discount and issuance costs on convertible senior notes 932 932 4,002 4,002 Exit costs related to closure and relocation of Russian operations — — (545) (545) Acquisition and related transaction costs and one-time integration costs(3) 3,736 2,736 8,972 7,972 Costs related to a reduction in force plan — — 7,766 7,766 One-time expenses related to strategic consulting services for operational review — — 1,265 1,265 Other cost-reduction and productivity initiatives 1,898 1,898 4,771 4,771 Legal fees related to the securities class action — — 509 509 Office closure lease termination costs — — 95 95 Income tax expense effects(4) — — — — Non-GAAP net income $ 56,233 $ 57,795 $ 221,944 $ 225,052 GAAP net income per share: Diluted $ 0.06 $ 0.12 $ 0.23 $ 0.30 Non-GAAP net income per share: Diluted $ 0.72 $ 0.74 $ 2.86 $ 2.90 Shares used in computing GAAP net income per share: Diluted 87,500 87,500 88,500 88,500 Shares used in computing non-GAAP net income per share: Diluted 78,100 78,100 77,700 77,700