Dilution calculator
We love cake. Carrot, chocolate, lemon drizzle. So what better way to think about your company than as a cake everyone wants a slice of? It has 100 slices. At the beginning, you own the whole thing, but over time, investors, advisors and core team members all take a slice. This calculator helps you model what you're left with and whether it's an exciting enough share.
New to this? Words like pre-money and dilution are explained on the vocabulary page. It takes two minutes.
You only need two numbers per round: what the company is worth before the money goes in, and how much money is coming in. If you do not know them yet, try 800k and 200k to see how it works.
Start with your company today
Step 1 of 2. Who owns the company now? If it is only you, leave these as they are.
Three checks that always work
Check 1. Post-money is always pre-money plus the new money. If your post-money is smaller than the pre-money, something is wrong.
Check 2. The new investor's share is always the money in divided by the post-money. Never divided by the pre-money. This is the most common mistake.
Check 3. All the shares must add up to 100%. Add them. If they do not, you missed someone.
UK rounds in 2025, by stage
Median figures for all UK equity deals in 2025. Half of rounds were bigger than this, half smaller. The last column is the sum from this page: round ÷ (pre-money + round).
| Stage | Median round | Median pre-money | Investor share if both are typical |
|---|---|---|---|
| Seed | £0.6m | £3.2m | 16% |
| Venture (Series A and B) | £1.1m | £8.2m | 12% |
| Growth | £2.6m | £22.3m | 10% |
Averages are much higher (seed average round £3.2m, average pre-money £6.0m) because a few very large deals pull them up. Use the median.
Source: British Business Bank, Small Business Equity Tracker 2026, figures 2.5 and 2.7 (published July 2026, data for calendar year 2025).
First rounds on SeedLegals
Founder-led first rounds, which are usually smaller than the market-wide figures above. This is closer to a university spin-out's first raise.
| What | Figure |
|---|---|
| Mean pre-money, first round | £2.89m |
| Usual range, first round | £1.4m to £5m |
| Mean pre-money, later rounds | £7.33m |
Source: SeedLegals Termometer, 2,000+ UK rounds, May 2024 to April 2025.
UK investment in 2025, by sector
Total equity investment into smaller UK businesses, and how it changed from 2024. No public UK source gives pre-money valuations by sector, so use the stage table above for your sums and this table to see where the money is going.
| Sector | Investment 2025 | Change vs 2024 |
|---|---|---|
| Digital and technologies | £9.3bn | +21% |
| Professional and business services | £2.1bn | 0% |
| Life sciences | £1.6bn | −23% |
| Financial services | £1.5bn | −12% |
| Advanced manufacturing | £0.6bn | +49% |
| Creative industries | £0.5bn | +1% |
| Clean energy | £0.5bn | +4% |
AI companies took £5.4bn of this, 44% of all investment into smaller businesses. Seed-stage deal numbers fell 27% in 2025, so first rounds are harder to get but not smaller.
Source: British Business Bank, Small Business Equity Tracker 2026, figures 2.12 and 2.13.
These are UK figures. Other markets can be very different. Check a local source before you use them in a negotiation.
Vocabulary
- Pre-money
- The price of the company before the new money goes in.
- Post-money
- Pre-money plus the new money.
- Equity
- Ownership. On this page, measured in slices out of 100.
- Dilution
- Your percentage going down because an investor took some of the slices.
- Round
- One investment, at one price, from one or more investors.
- Term sheet
- The short document that sets out the deal before the lawyers write the long one.
Three terms to ask a lawyer about before you sign
- Liquidation preference
- When the company is sold, the investor gets their money back first. You get what is left.
- Option pool
- Slices set aside for future staff. If the pool is created before the round, the slices come from you, not the investor.
- Anti-dilution
- If a later round has a lower price, the investor gets extra slices so their share does not drop as much. Yours drops more.
This page does not model any of these three terms.
Made by GuessWorks. We train founders and researchers to pitch, raise and keep their slices. This page is a teaching aid, not financial or legal advice.