Cap table calculator
Founder Dilution Calculator
Estimate how new investor ownership and option pool expansion reduce existing founder ownership on a simplified fully diluted basis.
Founder dilution formula on this page
Founder ownership after = founder ownership before × (1 − new investor ownership − option pool top-up). All inputs are percentages of the fully diluted company in this educational model. The calculator is meant for quick “what happens to my percent?” checks, not legal cap-table administration.
New investor ownership often comes from a priced-round raise (investment ÷ post-money). Option pool top-up is the incremental pool created in the round. Existing pool already reflected in the before-round founder percentage should not be double-counted as a top-up.
Worked example: 80% founders, 20% new money, 10% pool top-up
Start with founders at 80% before the round. Sell 20% to a new investor and create a 10% option-pool top-up on the simplified post-round pie. The remaining factor for existing holders is 1 − 0.20 − 0.10 = 0.70.
Founder ownership after = 80% × 0.70 = 56%. That is a 24 percentage-point drop from 80% to 56%, or relative dilution of 24 ÷ 80 = 30% of the founders’ prior stake. If the pool top-up is 0% instead, founders would land at 80% × 0.80 = 64% after the same 20% primary sale.
When to pair other calculators
- Derive investor ownership from dollars with the valuation calculators.
- Size pool shares and pre-money vs post-money treatment with the Option Pool Calculator.
- Estimate convertible overhang with the SAFE or convertible note tools before folding ownership into this view.
Educational-use disclaimer: FounderMath is for educational planning only. It is not legal, tax, accounting, investment, securities, financial, or fundraising advice.
Related tools
Cap table hub · Option Pool Calculator · Option Pool Shuffle · Pre/Post-Money Calculator · SAFE Conversion Calculator
FAQ
What does founder ownership after the round mean here?
It is the simplified post-round founder percentage after subtracting new investor ownership and any option-pool top-up percentage from the fully diluted pie, then applying that remaining factor to the founder ownership before the round.
How should I enter option pool top-up percent?
Enter the incremental pool percentage created in the round on a fully diluted post-round basis in this simplified model. If there is no pool expansion, leave the top-up at 0%.
Is this the same as an equity dilution calculator?
It targets founder-oriented dilution math and can answer equity-dilution style questions when you know starting founder ownership, new investor ownership, and pool expansion. It is not a full multi-class cap table.
Does this include SAFE or note conversion shares?
No. Convertibles should be estimated on the SAFE or convertible note calculators first, then reflected here as part of new ownership if you are doing a rough combined scenario.
Can two founders split the result?
Yes for planning: run the calculator with combined founder ownership, then allocate the after-round percentage in the same relative ratio the founders held before the round, unless a different agreement says otherwise.
Last reviewed September 7, 2026. See Methodology and Sources.