Startup Dilution Calculator
Every time you raise, you sell a slice of the company — and the details decide how big that slice really is. This calculator turns a round into clear numbers: enter your pre-money and the amount you're raising, and see the post-money cap table, the new investors' stake, and exactly how much ownership you walk away with.
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Methodology
How it works
How dilution is calculated
Post-money valuation is simply your pre-money valuation plus the new investment. The new investors' ownership is their cheque divided by that post-money figure — so a $2M round at an $8M pre-money is $2M / $10M, or 20%. Every existing shareholder is diluted in proportion: if you owned 100% before, you own 80% after.
Working in valuation and percentages (rather than exact share counts) is how founders reason about a raise on the back of an envelope. The arithmetic is intentionally transparent so you can sanity-check any term sheet against it.
The option pool shuffle — the part founders miss
Investors almost always require an employee option pool to be created or topped up as part of the round, and they want it counted in the pre-money. That means the pool is carved out of the existing shareholders' equity — the founders — not the incoming investor. A 10% post-money pool can therefore cost you several extra points of ownership on top of the investor's stake.
This calculator models the pool the standard (pre-money) way, so the dilution you see is the dilution you'll actually feel. If you can negotiate the pool into the post-money instead, you keep more — it's one of the highest-leverage terms in a seed deal.
Priced rounds, SAFEs and notes
A priced equity round and a post-money SAFE both behave the way this model shows: the investor's percentage is fixed at the cap relative to the post-money. Pre-money SAFEs and convertible notes are fuzzier — they convert later, and stacking several of them can dilute you more than expected once they all convert at the priced round. Use this as your priced-round baseline, then model conversions separately.
FAQ