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Option Pool Calculator

Convert your post-money SAFEs, top up the option pool and price the round. See founder dilution, every formula, and what the option pool shuffle costs you.

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How it works

Fill in today's fully diluted share counts, each post-money SAFE, and the priced round from your term sheet. The calculator converts the SAFEs, solves the pool top-up and round price together, and prints each step with your numbers. It then runs the same round with the pool added after the money so you can see what the option pool shuffle costs.

Formulas

SAFE ownership at the cap: each capped SAFE buys amount ÷ post-money cap of the company capitalization.
Company capitalization C = issued shares + options outstanding + promised options + unissued pool + all SAFE conversion shares. It excludes the new money and the pool increase. With only capped SAFEs converting at their caps, C = shares before SAFEs ÷ (1 − Σ amount ÷ cap).
Safe price = post-money cap ÷ C. Discount price = round price × (1 − discount). Each SAFE converts at the lower price that applies to it; an uncapped SAFE with no discount converts at the round price. When any SAFE converts below its cap, C changes, so the tool iterates until every share count settles.
Pool in the pre-money (shuffle): investor share f = investment ÷ (pre-money + investment). Post-round total T = (C − U) ÷ (1 − f − target), pool increase ΔP = target × T − U (zero if the existing pool already meets the target), round price = pre-money ÷ (C + ΔP), new shares = f × T.
Pool after the money: round price = pre-money ÷ C, new shares = investment ÷ price, then ΔP = (target × (C + new shares) − U) ÷ (1 − target). New investors are diluted by the pool too, so they own less than investment ÷ post-money.
Effective pre-money = round price × C: what the shares that existed before the round are worth at the round price. The gap to the headline pre-money is the pool increase × round price.

Shares are rounded down to whole shares. Exact solve keeps the pool increase unrounded so the target lands on exactly the percentage you entered. Like YC's guide rounds the pool increase up to the next 1,000 shares and the price to four decimals, as YC's worked example does.

Rules and sources (checked 2 Nov 2026)

Rule	What the source says	Source
Safe Price	Post-money valuation cap ÷ Company Capitalization	YC Post-Money SAFE User Guide, Section B, Questions 3 and 4
Lower price wins	The SAFE converts at whichever price gives the investor more shares: the Safe Price or the price new investors pay (discounted, for a SAFE with a discount)	YC User Guide, Section B, Question 3; discount forms on YC SAFE documents
Company Capitalization	Includes issued stock, outstanding and promised options, the unissued pool and converting securities; excludes the option pool increase in the equity financing (except to cover promised options above the pool) and the new money	YC User Guide, Section C, Question 1, and Example 1
Pool in the pre-money	Example 1's $15M pre-money includes an unallocated pool of 10% of the post-closing fully diluted capitalization and the SAFE conversion shares	YC User Guide, Appendix II, Example 1
Round price	Pre-money ÷ (fully diluted shares after SAFE conversion + option pool increase)	YC User Guide, Example 1
Non-US SAFEs	YC publishes valuation-cap versions for Canada, the Cayman Islands and Singapore, and says to consult a local lawyer	YC SAFE documents

What it does not model

Pre-money SAFEs, convertible notes and interest, MFN amendments, pro rata side letters (an investor buying into the new round shows up inside "New investors"), promised options above the pool, liquidation preferences and anti-dilution. Canadian and Australian founders: the math is the same for any instrument that uses YC's post-money definitions, including YC's Canada form. There is no YC Australian form, so check a local instrument's definitions first.

Educational model, not legal, tax or investment advice. Your lawyer's closing cap table is the one that counts.

Related guides and files

Worked example

YC's Example 1 (the default inputs): founders hold 9,250,000 shares, with 300,000 options outstanding, 350,000 promised and 100,000 unissued, for 10,000,000 fully diluted. Investor A buys a $200,000 SAFE at a $4M post-money cap (5%) and Investor B $800,000 at an $8M cap (10%).

Company capitalization = 10,000,000 ÷ (1 − 15%) = 11,764,705. Safe prices are $4M ÷ 11,764,705 = $0.34 and $0.68, so the SAFEs convert into 588,235 and 1,176,470 shares.
Series A: $5M at $15M pre-money, so new investors own 25%, with a 10% unissued pool after closing. T = (11,764,705.9 − 100,000) ÷ (1 − 25% − 10%) = 17,945,701, so the pool grows by 1,694,570 shares (YC rounds to 1,695,000) and the price is about $1.1145 ($1.1144 in YC's rounding).
After the round the founders own 51.54%, Investor A's SAFE 3.28%, Investor B's SAFE 6.56%, options outstanding 1.67%, promised options 1.95%, new investors 25.00% and the pool 10.00%. These are the figures in YC's own table.
The shuffle: at the round price, the 11.76M pre-round shares are worth about $13.11M, not $15M. Adding the same 10% pool after the money instead would leave the founders with about 53.41%.

Frequently asked questions

What is the option pool shuffle?

It is when a term sheet requires the option pool to be created or topped up inside the pre-money valuation. The new pool shares count before the round price is set, so the price per share drops and the cost of the pool falls on the existing holders (founders, employees and converting SAFE holders), not on the new investors. In YC's Example 1 the headline pre-money is $15M, but the shares that existed before the round are worth about $13.1M at the round price.

How do I calculate option pool dilution?

With the pool in the pre-money, solve two equations together: new investors own investment ÷ post-money of the post-round total, and the unissued pool (old plus new) equals your target percent of that same total. Total shares T = (C − U) ÷ (1 − investor % − target %), where C is company capitalization and U the existing unissued pool. The pool increase is target % × T − U.

Does the option pool increase dilute post-money SAFE holders?

Yes. Under YC's post-money SAFE, company capitalization includes the existing unissued pool but excludes the option pool increase made in the priced round. So the SAFEs convert first, and then the new pool and the new money dilute them along with the founders. In YC's Example 1, Investor A's 5% becomes 3.28% after the Series A.

What option pool size do investors ask for?

Commonly 10% to 15% of the post-round fully diluted company at seed or Series A, with 10% the most frequent figure in the example YC uses. The better number is the one your 12 to 24 month hiring plan needs, because every point of pool you create in the pre-money comes out of the existing holders.

Is a post-money SAFE more dilutive than a pre-money SAFE?

Usually, for the founders. A post-money SAFE fixes the investor's percentage (amount ÷ post-money cap) of a capitalization that already includes every other converting SAFE, so each new SAFE dilutes the founders rather than the earlier SAFE holders. This calculator models post-money SAFEs only.

Does this work for Canadian or Australian companies?

The arithmetic is the same wherever the instrument uses YC's post-money conversion. YC publishes valuation-cap SAFEs for companies formed in Canada, the Cayman Islands and Singapore, and says to use a local lawyer. It publishes no Australian version, so an Australian company on a locally drafted SAFE should check that its definitions match before relying on these numbers.

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