Investor Presentation November 2023

Non-GAAP Financial Information In addition to our results under GAAP, in this presentation we also present certain other supplemental financial measures of financial performance that are not required by, or presented in accordance with, GAAP, including, Consolidated Adjusted EBITDA, Consolidated Adjusted EBITDA margin, Adjusted Net Income (Loss) and Adjusted Net Income (Loss) per Share. We calculate Consolidated Adjusted EBITDA as net income (loss) before interest expense, income tax expense (benefit) and depreciation and amortization, adjusted for the impact of certain other items, including stock-based compensation expense and acquisition-related costs, as set forth in greater detail in this appendix. We calculate Consolidated Adjusted EBITDA margin as Consolidated Adjusted EBITDA divided by revenue. We calculate Adjusted Net Income (Loss) as net income (loss) before amortization of intangible assets, stock-based compensation expense, fair value changes to financial instruments and contingent earnouts, and other gain or losses, as set forth in greater detail in this appendix. Adjusted Net Income (Loss) per Share represents Adjusted Net Income (Loss) attributable to stockholders divided by the weighted average number of shares of common stock outstanding during the applicable period. Consolidated Adjusted EBITDA is one of the primary metrics used by management to evaluate our financial performance and compare it to that of our peers, evaluate the effectiveness of our business strategies, make budgeting and capital allocation decisions and in connection with our executive incentive compensation. Adjusted Net Income (Loss) and Adjusted Net Income (Loss) per Share are useful metrics to evaluate ongoing business performance after interest and tax. These measures are also frequently used by analysts, investors and other interested parties to evaluate companies in our industry. Further, we believe they are helpful in highlighting trends in our operating results because they allow for more consistent comparisons of financial performance between periods by excluding gains and losses that are non-operational in nature or outside the control of management, and, in the case of Consolidated Adjusted EBITDA, by excluding items that may differ significantly depending on long-term strategic decisions regarding capital structure, the tax jurisdictions in which we operate and capital investments. These non-GAAP measures do, however, have certain limitations and should not be considered as an alternative to net income (loss), earnings (loss) per share or any other performance measure derived in accordance with GAAP. Our presentation of Consolidated Adjusted EBITDA, Adjusted Net Income (Loss) and Adjusted Net Income (Loss) per Share should not be construed as an inference that our future results will be unaffected by unusual or non-recurring items for which we may make adjustments. In addition, Consolidated Adjusted EBITDA, Adjusted Net Income (Loss) and Adjusted Net Income (Loss) per Share may not be comparable to similarly titled measures used by other companies in our industry or across different industries, and other companies may not present these or similar measures. Management compensates for these limitations by using these measures as supplemental financial metrics and in conjunction with our results prepared in accordance with GAAP. We encourage investors and others to review our financial information in its entirety, not to rely on any single measure and to view Consolidated Adjusted EBITDA, Adjusted Net Income (Loss) and Adjusted Net Income (Loss) per Share in conjunction with the related GAAP measures. Additionally, we have provided estimates regarding Consolidated Adjusted EBITDA for 2023. These projections account for estimates of revenue, operating margins and corporate and other costs. However, we cannot reconcile our projection of Consolidated Adjusted EBITDA to net income (loss), the most directly comparable GAAP measure, without unreasonable efforts because of the unpredictable or unknown nature of certain significant items excluded from Consolidated Adjusted EBITDA and the resulting difficulty in quantifying the amounts thereof that are necessary to estimate net income (loss). Specifically, we are unable to estimate for the future impact of certain items, including income tax (expense) benefit, stock-based compensation expense, fair value changes and the accounting for the issuance of the Series A-2 preferred stock. We expect the variability of these items could have a significant impact on our reported GAAP financial results. This presentation also includes Net debt, a non-GAAP measure which represents total debt (excluding deferred debt issuance costs) less cash and restricted cash. Management uses Net debt as one of the means by which it assesses financial leverage and capitalization, and it is therefore useful to investors in evaluating our business using the same measures as management. This measure is also useful to investors because it is often used by securities analysts and other interested parties in evaluating our business. The measure does, however, have certain limitations and should not be considered as an alternative to or in isolation from gross debt and cash or any other measure calculated in accordance with GAAP. Other companies, including other companies in our industry, may not use Net debt in the same way or may calculate it differently than as presented herein. This presentation also includes Adjusted Operating Cash Flow, a non-GAAP measure which represents cash flow provided by (used in) operating activities less amounts paid for acquisition-related contingent consideration. Payments for acquisition- related consideration are not part of the Company's day-to-day operations and management uses this measure to assess the Company's operating cash flow without the impact of these unique, non-operational payments. This measure does, however, have certain limitations as the excluded acquisition-related payments are typically paid in cash and, as a result, impact the Company's liquidity as a whole, and should therefore not be considered as an alternative to or in isolation from cash flow provided by (used in) operating activities or any other liquidity measure calculated in accordance with GAAP. Other companies, including other companies in our industry, may not use this measure in the same way or may calculate it differently than as presented herein. This presentation also presents revenues on a last twelve month ("LTM") basis. Information presented for LTM periods that do not track our fiscal year (i.e., the LTM period ended Q3 2023) reflect unaudited trailing four quarter financial information calculated by starting with the results from the most recent audited fiscal year included in such LTM period and then (x) adding quarterly information for subsequent fiscal quarters and (y) subtracting quarterly information for the corresponding prior year period. For each line item shown, LTM Q3 2023 has been calculated by taking the relevant reported financial information from Fiscal 2022 and adding the reported financial information for the nine months ended September 30, 2023, and then subtracting the reported financial information for the nine months ended September 30, 2022. This presentation is not in accordance with GAAP. However, we believe LTM information is useful to investors as we use it to evaluate our financial performance for ongoing planning purposes, including a continuous assessment of our financial performance in comparison to budgets and internal projections. This presentation has limitations as an analytical tool, and you should not consider it in isolation or as a substitute for analysis of our results as reported under GAAP. Please see our Annual Report on Form 10-K filed on March 1, 2023 and Quarterly Report on Form 10-Q filed on November 8, 2023, respectively, for the historical amounts used to calculate the LTM information presented. In this presentation we also reference our organic growth. We define organic growth as the change in revenues excluding revenues from i) our CTEH environmental emergency and/or disaster response business, ii) acquisitions for the first twelve months following the date of acquisition and iii) businesses held for sale, disposed of or discontinued. As a result of the potential annual volatility in CTEH's revenues due to the emergency response aspect of their business, we will no longer be including CTEH revenues in the calculation of organic growth. Management uses organic growth as one of the means by which it assesses our results of operations. Organic growth is not, however, a measure of revenue growth calculated in accordance with GAAP, and should be considered in conjunction with revenue growth calculated in accordance with GAAP. We have grown organically and expect to continue to do so. © 2023 Montrose Environmental Group, Inc. Proprietary. | 25