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Startup Dilution Calculator

Model up to four future rounds with option pool top-ups and see what founders and each group of investors own after every round.

Inputs

Reset

Ownership today

Anything left over is treated as earlier investors (for example, converted SAFEs).

Seed

Unissued pool as a percent of post-money. Topped up before the round if it would fall short. 0 for none.

Series A

Series B

Series C

Leave at 0 to skip this round

Results

Founder ownership after Series B

42.1%

Down from 90.0% today, a loss of 47.9 percentage points.

Founders’ stake on paper
$63,106,061
At the $150M post-money
Share of founder stake given up
53.3%
All investors combined
47.9%
Total raised
$43,000,000
Last post-money valuation
$150,000,000
Option pool at the end
10.0%
Ownership after each round
Round by round
RoundPost-moneyNew moneyPool top-upFounders
Seed$15M20.0%2.2%70.0%
Series A$50M20.0%4.4%52.9%
Series B$150M20.0%0.5%42.1%

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The math

How dilution adds up

Every priced round issues new shares. Nobody loses shares, but everyone who already owns a piece ends up with a smaller percentage of a bigger company.

  1. New investors buy their stake. They own the raise divided by the post-money valuation (pre-money plus the raise).
  2. The option pool gets topped up. If the existing unissued pool would end the round below the target, new pool shares are created before the round so the pool lands exactly on the target.
  3. Everyone else shrinks pro rata. Founders, earlier investors and the old pool all scale down by the same factor, and the next round starts from there.

The chart stacks each group's ownership after every round so you can watch the founders' share shrink and each new investor class appear. The worked example uses the default inputs ($3M seed, $10M Series A, $30M Series B).

New investor stake  = raise / (pre-money + raise)
Pool top-up T       = (target - pool x (1 - stake)) / (1 - stake - target)
Each holder keeps   = (1 - stake) / (1 + T) of their percent

Assumptions and simplifications

  • Priced equity rounds only. SAFEs and notes are not converted here; include them in earlier investors or use the SAFE conversion calculator.
  • The pool target is the unissued pool after the round. Grants made between rounds are not modeled, so the pool only shrinks through dilution.
  • Existing investors are assumed not to buy into later rounds (no pro rata participation), and there are no secondary sales, down-round protections or warrants.
  • Founders’ stake “on paper” is ownership times the last post-money valuation, before any liquidation preferences.

Worked example

Seed: $3M on a $12M pre-money

New investor stake
$3M / $15M = 20.0%
Pool without a top-up
10% x 80% = 8.0%
Pool top-up (as % of post)
2.22%
Founders keep
90% x 77.78% = 70.0%
After Series A
52.9%
After Series B
42.1%
Founders after Series B42.1%

Further reading

Frequently Asked Questions

Common questions about the Dilution calculator and the math behind it.

How much dilution is normal per round?

Each round sells new investors a slice equal to the raise divided by the post-money valuation, so a round that raises $3M at a $15M post-money sells 20%. The option pool top-up comes on top of that. Rather than relying on a rule of thumb, plug in the raise and valuation you expect and see the result for each round.

Why does the option pool top-up dilute founders but not new investors?

Term sheets usually ask for the expanded pool to be created before the new money comes in, so it counts in the pre-money share count. That lowers the price per share for the new investors and leaves the whole cost of the top-up with the existing holders. This calculator models the top-up that way.

Does dilution mean my stake is worth less?

Not necessarily. Dilution lowers your percentage, but if the round is priced above the last one, each share is worth more and a smaller slice of a larger company can be worth more on paper. The calculator shows the founders’ stake at the last post-money valuation for that reason.

Are SAFEs and convertible notes included?

Not directly. If SAFEs or notes will convert at the first priced round, leave room for their expected ownership in the "earlier investors" share (100% minus founders and the pool), or use the SAFE conversion calculator first to estimate it. Anti-dilution adjustments and down rounds are not modeled.

How do I model a round I am not sure about?

Set its raise to zero and it is skipped. Every field is saved in the page URL, so you can copy the link for each scenario and compare them side by side.

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