Startup dilution calculator

See who owns what after each funding round, and what the option pool shuffle costs founders when the new pool is counted in the pre-money. Everything runs in this browser tab; nothing is sent anywhere.

How it's calculated

For each round, with S fully diluted shares before the round (pool included), pre-money V, raise R, existing pool P and a target pool of p of post-money shares:

• Pool in pre-money (shuffle): new pool shares T = (p × (V+R)/V × S − P) / (1 − p × (V+R)/V). Price per share = V / (S + T). The investor buys R / price shares and owns exactly R / (V+R). The top-up dilutes only the existing holders.
• Pool in post-money: price per share = V / S, the investor buys R / price shares, then T = (p × (S + investor shares) − P) / (1 − p). The top-up dilutes everyone, the new investor included.
• A pool already at or above the target is left alone. Investors are assumed not to buy their pro-rata in later rounds.

Example: 9M founder shares, a 1M pool, $8M pre-money, $2M raise, 20% pool target. In the pre-money, the pool tops up by 2M shares, the price is $0.667, and founders keep 60.0%. In the post-money, founders keep 62.6%. The shuffle costs them 2.6 points.

Beyond dilution

Ownership is half the story. CapStack GP takes the same cap table through SAFEs and notes, liquidation preferences and the exit waterfall, then shows what each holder is paid at each exit value.

Related: SAFE conversion calculator · Exit waterfall calculator · Rule of 40 and Rule of X calculator

Illustrative model only. Not legal, tax, or investment advice. Real rounds also turn on SAFE conversion, anti-dilution and the exact pool definition in the term sheet.