Dilution calculator

Dilution is the fall in an existing shareholder's percentage when new shares are issued. You keep the same shares, but they are a smaller slice.

The formula

Dilution = existing shares ÷ all shares after the round

Worked example: 70.0% kept by existing shareholders, down from 100.0%

The example uses the guide's seed round, £200,000 for 20%, with a matching cap table, exit, fund and market.

1,000,000 existing shares ÷ 1,428,571 shares after the round = 70.0%
Down 30.0 percentage points

Try it with your numbers

Work out your dilution

It starts on the example. Replace any figure with your own; nothing you type leaves your browser.

Your deal numbers

Start with any one figure. Each one you add works out more below. Your numbers are kept in this browser only.

What this calculation uses

Pre-money valuation (needed)

You can type 2m or 750k.

New investment (needed)

Shares in issue (needed)

Options already granted

Unallocated option pool

In shares. 0 if you have none.

Option pool wanted after the round

Add more of your numbers

Open a group to fill it in. Everything you add shows up in the list below the calculator.

An investment offer

Investment offered

For this share of the company

Your round

Your own shares

Money converting at the round

Amount converting

From an ASA, SAFE or loan note.

Valuation cap

Leave blank for no cap.

Discount

Interest a year (loan notes)

Months since the note was issued

A sale of the company

Sale price of the company

What the preferred investor put in

What the preferred investor owns

1x2x

Participating preference

What the founders own

An investor's return

Amount invested

Share bought

Later dilution

30 means later rounds shrink that share by 30%.

Sale price at the exit

Years to the exit

The next round

Share you own now

Size of the next round

Its pre-money valuation

Last round's post-money

New round's pre-money

A venture fund

Fund size (committed)

Paid in by investors so far

Invested in companies so far

Paid back to investors

Value of what the fund still holds

Your market

Potential customers

What one pays a year

Share you can serve

Share of those you could win

A SEIS, EIS or VCT investment

Amount an investor puts in

Shares that vest

Shares or options granted

Vesting period

Cliff

Months worked so far

Your dilution

70.0%

kept by existing shareholders, down from 100.0%

1,000,000 existing shares ÷ 1,428,571 shares after the round = 70.0%
Down 30.0 percentage points

Formula: Existing shares ÷ all shares after the round.

Diluted by: 30.0 points
Price per share: £0.70

How to read your result

Being diluted is fine if the company is worth more after the round. What matters is the value of your slice, not only its size.

Watch out for

An option pool top-up inside the pre-money often dilutes founders more than the investor does.

Last checked 24 October 2026. Estimates only, not financial, tax or legal advice: check your accounts and documents, and take advice before you act. More terms in the startup glossary.