Main Street Capital Fixed Income Presentation Deck

At-The-Market (ATM) Equity Program ATM Equity Program provides efficient and low cost access to equity capital Provides access to equity capital to match growth of LMM investments on an as- needed basis Provides significant economic cost savings compared to traditional overnight equity offerings Issued equity is accretive to NAV per share Provides permanent capital to match indefinite or long-term holding period for LMM investments Facilitates maintenance of conservative leverage position ● MAIN ST Provides significant benefits vs traditional overnight equity offerings CAPITAL CORPORATION Provides equity capital and liquidity on an as-needed basis, avoiding dilution from larger overnight equity offerings Provides equity capital at significantly lower cost Avoids negative impact to stock price from larger overnight equity offerings (1) Through June 30, 2023 (2) Assumes 6% all-in cost for traditional overnight equity offering Main Street Capital Corporation Raised net proceeds of $912.8 million since inception in 2015 (1) Average sale price is approximately 61% above average NAV per share over same period (1) NYSE: MAIN Resulted in economic cost savings of approximately $46.1 million when compared to traditional overnight equity offering(1)(2) mainstcapital.com Page 21

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