Does this account for an option pool?

No — a pool created or expanded as part of the round (common in venture deals) dilutes existing holders further than this basic calculation shows. Add that as a separate, larger effective round if your term sheet includes one.

What's the difference between pre-money and post-money valuation?

Pre-money is what the company is worth before the new investment; post-money is pre-money plus the new investment — the new investor's ownership % is investment ÷ post-money.

Does this work for SAFEs or convertible notes?

Not directly — those convert into shares at a later priced round under their own specific terms (a valuation cap, discount, or both), which this calculator doesn't model.

How do multiple funding rounds compound?

Multiplicatively — run this calculator once per round, using the previous round's ending ownership % as the next round's starting ownership %, since each round dilutes the ownership from after the prior round.

Is this the same as what a cap-table software tool shows?

The core math is the same, but dedicated cap-table tools also track share classes, liquidation preferences, vesting, and option pools — this is a simplified single-round illustration.

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Finance

Equity Dilution/Cap Table Calculator

How a funding round dilutes existing ownership — new % = old % × pre-money ÷ post-money.

🔒 Runs entirely in your browser — nothing here is ever uploaded

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Last reviewed 2026-08-30

About the Equity Dilution/Cap Table Calculator

Calculates how a new funding round dilutes an existing shareholder's ownership percentage — from shares outstanding, current ownership %, the round's pre-money valuation, and the new investment amount.

100% Free Runs in Your Browser No Sign-Up Required

How to use it

Enter total shares outstanding before this round.
Enter your (or the shareholder's) ownership % before this round.
Enter the round's pre-money valuation and the new investment amount.
Read your ownership % after the round, and how many points you were diluted.

Formula

Post-money valuation = pre-money + investment. Price per share = pre-money ÷ shares outstanding. New shares issued = investment ÷ price per share. New ownership % = old ownership % × (pre-money ÷ post-money) — every existing holder dilutes by this same ratio regardless of how many shares they hold, since new shares are issued at one shared price for the whole round.

Worked example

A founder with 100% of 10,000,000 shares, an $8M pre-money valuation, and a $2M new investment: post-money is $10M, price per share is $0.80, 2,500,000 new shares are issued, and the founder's ownership dilutes from 100% to exactly 80% (100% × 8/10).

Dilution factor by round size (illustrative)

Dilution factor by round size (illustrative)
Investment ÷ Pre-money	New investor %	Existing holder retains
10%	9.1%	90.9% of prior ownership
25%	20%	80% of prior ownership
50%	33.3%	66.7% of prior ownership

Interpreting your result

This models a single, simple priced round only. It doesn't account for an option pool top-up (commonly created or expanded right before a round, which dilutes existing holders further than this alone shows), convertible notes/SAFEs converting at the same close, or multiple share classes with different rights/preferences. Not legal or investment advice — a real cap table needs a lawyer or dedicated cap-table tool for anything binding.

Recommendations

• Dilution depends only on the investment-to-pre-money ratio, not on how many shares you personally hold — a 25% raise relative to pre-money dilutes every existing holder to 80% of their prior ownership, whether they held 1% or 40%.
• Watch for an option pool being created or expanded 'pre-money' — investors often require this, and it dilutes existing holders on top of the investor's own new shares, which this simple calculator doesn't add in.
• Multiple rounds compound multiplicatively, not additively — model each round in sequence, feeding one round's ending ownership % into the next round's starting ownership %.

Frequently asked questions

Because new shares are issued at one shared price per share for the whole round — the ratio of new shares to the post-round total is fixed by the investment-to-pre-money relationship, not by any individual holder's stake.