Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 127

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 127
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 pro forma net tangible book value of $9.22 per share to new investors purchasing shares of common stock in this offering. Dilution per share to new investors is determined by subtracting pro forma as adjusted net tangible book value per share after this offering from the initial public offering price per share paid by new investors. The following table illustrates this dilution (without giving effect to any exercise by the underwriters of their option to purchase additional shares):

| Assumed initial public offering price per share                                                          
 Historical net tangible book deficit per share as of September 30, 2024                                  
 Pro forma increase in net tangible book value per share as of September 30, 2024 attributable to the pro 
 forma adjustment described above                                                                         |     |     | (31.46 
  37.09 | ) |     |   | 17.00 |
|:---------------------------------------------------------------------------------------------------------|:----|:----|-------:|:--|:----|:--|------:|
| Pro forma net tangible book value per share as of September 30, 2024                                     |     |     |   5.63 |   |     |   |       |
| Increase in pro forma net tangible book value per share attributable to new investors participating in   
 this offering                                                                                            |     |     |   2.15 |   |     |   |       |
| Pro forma as adjusted net tangible book value per share after this offering                              |     |     |        |   |     |   |  7.78 |
| Dilution per share to new investors in this offering                                                     |     |     |        |   |     | $ |  9.22 |

The dilution information discussed above is illustrative only and may change based on the actual initial public offering price and other terms of this offering. Each $1.00 increase or decrease, as applicable, in the assumed initial public offering price of $17.00 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, the pro forma as adjusted net tangible book value per share after this offering 91

by $0.20, and dilution in pro forma net tangible book value per share to new investors by $0.80, assuming that the number of shares of common stock offered by us, as set forth on the cover page of this prospectus, remains the same, and after deducting underwriting discounts and commissions and estimated offering