Key takeaways
- Price per share is the pre-money valuation divided by the shares inside the pre-money. New investors get investment ÷ price shares.
- With no pool and no SAFEs, the new investors own investment ÷ (pre-money + investment), and everyone else is diluted by the same proportion.
- A pool top-up in the pre-money lowers the price, so existing holders pay for it. A top-up after the money is shared with the new investors.
- Ownership is not payout. Liquidation preferences, vesting and later terms decide who receives what in a sale.
How to use the dilution calculator
- 1List today's fully diluted cap table: founders, employees with granted options, earlier investors and the unallocated option pool, each with their shares or options.
- 2Pick the currency and enter the round: its name, the pre-money valuation and the new money invested.
- 3Set the option pool target, the unallocated pool you want after the round as a share of all shares, or 0 for none. Choose whether the top-up sits in the pre-money or comes after the money.
- 4Add any post-money SAFEs that convert in this round, with their amount, cap and discount. Add up to two later rounds if you want to see dilution over time.
- 5Read ownership before and after each round, open the formula with your numbers, and copy the summary.
The formulas behind each round
Shares are kept as fractions so the percentages are exact. Real documents round share counts, so a signed cap table can differ by a few shares.
| Quantity | Formula |
|---|---|
| Shares before the round (E) | Issued shares + granted options + unallocated pool |
| Price per share, pool top-up in the pre-money | Pre-money ÷ (E + SAFE shares + top-up) |
| Price per share, pool top-up after the money | Pre-money ÷ (E + SAFE shares) |
| New investor shares | Investment ÷ price |
| Top-up in the pre-money | (t × k × (E + SAFE shares) − existing pool) ÷ (1 − t × k), where t is the pool target and k = 1 + investment ÷ pre-money |
| Top-up after the money | (t × (E + SAFE shares + new investor shares) − existing pool) ÷ (1 − t) |
| A holder's ownership after | Their shares ÷ shares after the round |
| Relative dilution | 1 − ownership after ÷ ownership before |
The top-up is never negative: if the unallocated pool already meets the target, nothing is issued.
Worked example: the same seed round with two pool positions
Two founders hold 4,500,000 shares each and the unallocated pool holds 1,000,000, so there are 10,000,000 shares. The company raises $2,000,000 at an $8,000,000 pre-money valuation, and the investors ask for a 10% unallocated pool after the round. Without any pool, each founder would go from 45% to 36%.
| Result | Top-up in the pre-money | Top-up after the money |
|---|---|---|
| Pool top-up | 285,714 shares | 277,778 shares |
| Price per share | $0.7778 | $0.8000 |
| New investor shares | 2,571,429 | 2,500,000 |
| Each founder after | 35.00% | 35.22% |
| New investors after | 20.00% | 19.57% |
| Unallocated pool after | 10.00% | 10.00% |
With the top-up in the pre-money, the new investors still get exactly 20%, and the founders carry the whole cost of the larger pool. The headline pre-money is $8,000,000, but the value of the shares that existed before the round is 10,000,000 × $0.7778, about $7,777,778. That gap is often called the option pool shuffle.
SAFEs and later rounds
A post-money SAFE, the standard Y Combinator form since 2018, converts at whichever price gives its holder more shares: the cap divided by the shares before the round plus all SAFE shares, the round price less any discount, or the round price. At its cap it owns its amount divided by the cap of the company just before the new money. The new investors and a pool top-up made in the round then dilute it like everyone else.
A later round starts from the cap table after the one before it, so you can see founders' ownership across seed and Series A in one place. For pre-money SAFEs, or to see each SAFE's candidate prices side by side, use the SAFE conversion calculator.
What the calculator leaves out
- Pre-money SAFEs, convertible notes with interest, warrants and side letters. Enter their converted shares as a holder if you know them.
- Liquidation preferences, participation and anti-dilution terms. They change who gets paid in a sale, not the share count shown here.
- Vesting, unvested shares that may return to the pool, and secondary sales.
- Pro rata rights. If an earlier investor takes part in a round, add their new money to the round and track it separately.
- Tax, legal and accounting effects. The result is an estimate, not legal, tax or investment advice. The signed documents decide.
Cap tables in Delsivo
Delsivo is an investment workspace for venture funds, not a cap table tool. In the pilot, a fund can send a founder a follow-up form from a template, including one for the cap table, and keep the answer on the deal record next to the deck and the fund's thesis. You don't need Delsivo to use this calculator. See founder requests and forms.
Sources
- Y Combinator: Safe financing documents (checked 6 November 2026)
- Y Combinator: Post-Money Safe User Guide (PDF) (checked 6 November 2026)
Facts about other companies and services come from the pages listed, on the dates shown, and can change.