Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 130

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 130
---
 in the case of a decrease, would decrease the percentage of total consideration paid by new investors to 28.7%, assuming that the assumed initial public offering price of $17.00 per share remains the same. The table above assumes no exercise of the underwriters’ option to purchase additional shares in this offering. If the underwriters’ option to purchase additional shares of our common stock is exercised in full, the number of shares of our common stock held by existing stockholders would be reduced to 75.9% of the total number of shares of our common stock outstanding after this offering, and the number of shares of common stock held by new investors purchasing common stock in this offering would be increased to 24.1% of the total number of shares of our common stock outstanding after this offering. The foregoing tables and calculations (other than the historical net tangible book value calculation) are based on 31,932,467 shares of common stock (which includes 119,639 shares of restricted common stock) outstanding as of September 30, 2024 after giving effect to the automatic conversion of outstanding shares of our preferred stock into 27,149,206 shares of common stock immediately prior to the completion of this offering, and excludes:

| • |     | 3,652,051 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 $5.77 per share;                                                   |

| • |     | 63,745 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 $10.33 per share;                                               |

| • |     | 1,099,636 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;                                   |

| • |     | 390,127 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 |

| • |     | 5,060,000 shares of our common stock that will