Free calculator
Startup dilution calculator
Work out who owns what after a priced funding round. Enter the pre-money valuation, the investment, the option pool the investor wants and your current shareholders, and see the new cap table.
Post-money valuation
£2,500,000
Price per share
£1.7500
to 4 decimal places
New investor owns
20.00%
285,714 new shares
| Holder | Shares before | Before | Shares after | After |
|---|---|---|---|---|
| Founder A | 600,000 | 60.00% | 600,000 | 42.00% |
| Founder B | 400,000 | 40.00% | 400,000 | 28.00% |
| Option pool (unallocated) | 0 | 0.00% | 142,857 | 10.00% |
| New investor | 0 | 0.00% | 285,714 | 20.00% |
| Total | 1,000,000 | 100% | 1,428,571 | 100% |
The 142,857 new pool shares are counted in the pre-money, so existing holders pay for them: their shares are effectively valued at £1,750,000, not the headline £2,000,000.
How it works
The post-money valuation is the pre-money valuation plus the investment, and the investor's share is the investment divided by the post-money valuation. New shares are issued to the investor at the round price, so everyone else's percentage falls even though their number of shares does not change.
Most term sheets also ask for an option pool of a set size after the round, created before the investment and counted in the pre-money valuation. That top-up dilutes only the existing shareholders, which lowers the effective price they get for their shares. Switch the pool to "post-money" to see the version where the investor shares that dilution.
Shares are whole numbers, so the calculator rounds new shares to the nearest share and works the percentages out from the rounded counts.
Worked example
Two founders hold 600,000 and 400,000 shares. An investor puts in £500,000 at a £2,000,000 pre-money valuation and asks for a 10% option pool after the round, counted in the pre-money.
The post-money valuation is £2,500,000, so the investor gets 20%. To leave 10% for the pool and 20% for the investor, the founders' 1,000,000 shares must be 70% of the company, so there are 1,428,571 shares after the round: 142,857 in the new pool and 285,714 for the investor. The price per share is £1.75, and the founders end with 42% and 28%.
Because the pool is paid for out of the pre-money, the founders' shares are effectively valued at £1,750,000 rather than £2,000,000. If the pool were counted in the post-money instead, the price would be £2.00, the founders would keep 43.2% and 28.8%, and the investor would end with 18%.
Assumptions
- One priced round of new ordinary or preference shares, all issued at the same price.
- Existing shareholdings are fully diluted: include granted options and any ASAs or loan notes that convert in this round as shareholders.
- The option pool percentage is the unallocated pool after the round, as a share of all shares.
- No anti-dilution adjustments, secondary sales or conversion discounts are applied.
- New shares are rounded to the nearest whole share.
Sources
Rates, limits and fees were checked on 21 October 2026.
Not financial advice. This calculator gives estimates for general information only. It does not know your full circumstances, and tax rules, rates and fees change. Check the official sources and speak to a qualified accountant, tax adviser or lawyer before you make a decision.