Company: BLLN
Filing Date: 2025-10-07
Form Type: S-1
Source: 0001193125-25-233697
Chunk: 135

Company: BillionToOne, Inc.
Filing Date: 2025-10-07
Form: S-1
Chunk 135
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, before deducting underwriting discounts and commissions and estimated offering expenses payable by us.

| (in thousands, except share and per share data and 
 percentages)                                       |     | Shares purchased 
 Number           |     | Percent |      |     | Total consideration 
 Amount              |     | Percent |      |     | Weighted- 
 average   
 price per 
 share     |
|:---------------------------------------------------|:----|:-----------------|:----|:--------|:-----|:----|:--------------------|:----|:--------|:-----|:----|:----------|
| Existing stockholders                              |     |                  |     |         | %    |     | $                   |     |         | %    |     | $         |
| New investors                                      |     |                  |     |         |      |     |                     |     |         |      |     | $         |
| Total                                              |     |                  |     |         | 100% |     | $                   |     |         | 100% |     |           |

The presentation in this table regarding ownership by existing stockholders does not give effect to any purchases that existing stockholders may make through our directed share program or otherwise purchase in this offering. If the underwriters exercise their option to purchase additional shares of Class A common stock in full, the number of shares held by the existing stockholders after this offering would be reduced to shares, or % of the total number of shares of our Class A common stock outstanding after this offering, and the number of shares held by new investors would increase to shares, or % of the total number of shares of our Class A common stock outstanding after this offering. 87

The foregoing discussion and calculations above (other than the historical net tangible book value calculations) are based on 35,616,629 shares of our Class A common stock and 4,552,650 shares of our Class B common stock outstanding as of June 30, 2025, after giving effect to the Preferred Stock Conversion, the Reclassification and the Class B Stock Exchange, in each case as if they had occurred on June 30, 2025, and excludes:

| • |     | 8,930,919 shares of our Class A common stock issuable upon the exercise of stock options outstanding as of 
 June 30, 2025 under our 2018 Plan, at a weighted-average exercise price of $10.59 per share;               |

| • |     | 1,224,