SAFE & Dilution Calculator

A SAFE is a promise of future shares. It converts when you raise a priced round, at a price set by its valuation cap, its discount, or the round price, whichever gives the investor the most shares. This calculator follows the definitions in YC's post-money SAFE.

The capitalization includes the SAFEs' own shares, so the maths is circular: you need the SAFE shares to know the price, and the price to know the shares. The calculator solves it by iterating until the numbers stop moving, usually in under 20 steps. The neat consequence of a post-money SAFE is that each investor ends up with almost exactly amount ÷ cap of the company just before the round.

The calculator's defaults are Example 1 from YC's own Safe User Guide (Appendix II): founders hold 9,250,000 shares, Investor A puts in $200k at a $4M post-money cap, Investor B puts in $800k at an $8M cap, then a $5M Series A at $15M pre-money with a 10% pool. Here is what the calculator gets next to YC's published numbers:

The small differences come from YC rounding the pool increase to a round 1,695,000 shares; the calculator keeps the exact value. The founders' result matches to two decimal places.

YC switched its standard SAFE to post-money in 2018. The difference is what the cap measures, which decides who absorbs dilution from SAFEs raised later.

The “pre-money (simplified)” option above prices the SAFE against your existing capitalization only. Older pre-money documents vary, so treat that mode as an estimate.

Investors usually ask for an unissued option pool of a set size after the round, and they count it in the pre-money. That means the new pool shares are paid for by existing holders, not the new money. In the worked example, the pool top-up is 1,694,570 shares, worth about $1,888,553 at the round price.

So the $15M headline pre-money is effectively $13,111,447 to the founders and SAFE holders. When you negotiate, size the pool to a real hiring plan for the next 18 months instead of accepting a round number.