Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 128

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 128
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 the percentage of total consideration paid by new investors to %, assuming that the assumed initial public offering price of $ per share remains the same. The foregoing tables and calculations (other than the historical net tangible book value calculation) are based on 46,656,571 shares of common stock (which includes 174,807 shares of restricted common 91

stock) outstanding as of September 30, 2024 after giving effect to the automatic conversion of outstanding shares of our preferred stock into 39,667,715 shares of common stock immediately prior to the completion of this offering, and excludes:

| • |     | 5,336,077 shares of common stock issuable upon exercise of outstanding stock options as of September 30, 2024 under our 
 2020 Plan, with a weighted average exercise price of $3.95 per share;                                                   |

| • |     | 93,141 shares of common stock issuable upon exercise of outstanding stock options granted after September 30, 2024 pursuant 
 to our 2020 Plan, with a weighted average exercise price of $7.07 per share;                                                |

| • |     | 1,606,629 shares of common stock reserved for future issuance as of September 30, 2024 under the 2020 Plan, which will 
 cease to be available for issuance at the time that our 2025 Plan becomes effective;                                   |

| • |     | shares of common stock reserved for future issuance under our ESPP, which will become effective                                                                                                                                                     
 on the date immediately prior to the effectiveness of the registration statement of which this prospectus forms a part, as well as any automatic increases in the number of shares of common stock reserved for future issuance under the ESPP; and |

| • |     | shares of our common stock that will become available for future issuance under our 2025 Plan,                                                                                                                                                     
 which will become effective on the date immediately prior to the effectiveness of the registration statement of which this prospectus forms a part, as well as any automatic increases in the number of shares of common stock reserved for future 
 issuance under the 2025 Plan and any shares underlying outstanding stock awards granted under the 2020 Plan that expire or are repurchased, forfeited, cancelled or withheld.                                                                      |

To the extent any outstanding options are exercised, new options or other equity awards are issued under our equity incentive plans, or we issue additional equity or convertible debt securities in the future, there will be further dilution to new investors.