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Equity Dilution Calculator

Enter your shares and the round details to see your diluted ownership.

How it is calculated

The tool compares your stake before and after the new shares appear. You enter your own share count, the total shares outstanding before the round, and the number of new shares issued:

before = your shares ÷ total before × 100
total after = total before + new shares
after = your shares ÷ total after × 100
dilution = before − after

The dilution figure is a difference in percentage points, not a relative loss of your stake. Your own share count is assumed not to change. Totals are plain share counts: options, convertible notes, SAFEs and pool top-ups only count if you have already added them into the totals yourself. Your shares cannot exceed the pre-round total and no value can be negative; otherwise there is no result.

Worked example

You hold 1,000,000 shares out of 10,000,000. Before the round that is 1,000,000 ÷ 10,000,000 = 10.0000%. The company issues 2,500,000 new shares, so the total becomes 12,500,000. Your stake is now 1,000,000 ÷ 12,500,000, which the tool shows as 8.0000%. The drop is 10.0000 − 8.0000 = 2.0000 percentage points, although relative to your original stake you gave up one fifth of it.

Try this example →

Common mistakes

  • Confusing percentage points with relative dilution. Going from 10% to 8% is 2 points of dilution, but your stake is 20% smaller in relative terms.
  • Entering the post-round total in the "total before" box. The new shares are added by the tool, so including them yourself counts them twice and understates the dilution.
  • Leaving out options, warrants or convertibles when you count the pre-round total. A fully diluted count gives a lower starting stake than a count of issued shares only.
  • Entering more of your own shares than the company total. That is impossible, so the tool shows no result; check that your shares are not larger than the pre-round total.
  • Typing the investment amount or valuation in the new shares box. That box expects a number of shares, not dollars.

Sources

About this calculator

When a startup issues new shares in a funding round, existing shareholders keep the same number of shares but now own a smaller slice of a bigger pie — this calculator computes your post-round ownership as your shares ÷ (total shares before the round + new shares issued), showing both your new percentage and how many percentage points you were diluted by.

Founders negotiating a term sheet, early employees evaluating stock options, and angel investors deciding whether to exercise pro-rata rights use this to understand the real cost of raising capital before signing: a $2M raise on an $8M pre-money valuation dilutes existing holders by 20%, for example, regardless of how the deal is framed. Anti-dilution provisions, option pool expansions, and convertible notes can change the exact math, but the core share-count ratio is the starting point for any dilution analysis.

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