Your SAFEs convert at the priced round, and the founders pay for most of it. Each post-money SAFE takes its amount divided by its cap of the company before the new money (Y Combinator). The pool increase the lead asks for sits in the pre-money. YC's guide leaves it out of the SAFE math, so it dilutes the founders and the SAFE holders but not the new investors. Enter your cap table, each SAFE, and the round below. You get every holder's percentage before and after. Not legal or tax advice.
What the calculator returns
| Output | Formula | Source |
|---|---|---|
| Company Capitalization (K) | Today's fully diluted shares + all SAFE conversion shares. Excludes new money and the round's pool increase | YC post-money safe user guide |
| SAFE cap price | Post-money cap ÷ K | YC |
| SAFE discount price | Round price × (1 − discount) | YC; Carta |
| SAFE conversion price | Lowest of cap price, discount price, and round price | YC; Carta |
| Pool increase | Target % × post-round shares − unissued pool today | YC worked example |
| Round price per share | Pre-money ÷ (K + pool increase) | YC worked example |
| New investor % | New money ÷ (pre-money + new money) | YC |
The tool solves for the round price and the SAFE shares together, because a discount SAFE's shares depend on the round price and the round price depends on the shares. It assumes YC post-money SAFEs, no notes, and no promised options above the unissued pool. If an investor has a pro rata side letter, put that money inside new money.
Three worked examples
All three start from 10,000,000 fully diluted shares.
| Example | Inputs | Founders after | SAFE holders after | New investors | Pool |
|---|---|---|---|---|---|
| 1. YC, round above the caps | Founders 92.5%, unissued pool 1%. SAFEs $200k at $4M and $800k at $8M. $5M at $15M pre, 10% pool | 51.54% | 3.28% and 6.56% | 25.00% | 10.00% |
| 2. YC, round below one cap | Same SAFEs. $2.2M at $8.8M pre, 10% pool | 55.31% (YC rounds to 55.32%) | 3.53% (cap) and 7.27% (round price) | 20.00% | 10.00% |
| 3. Editorial, discount SAFEs | Founders 90%, pool 10%. $1M at $20M cap with 20% discount and $500k discount-only at 20%. $3M at $12M pre, 15% pool | 52.50% | 8.33% and 4.17% | 20.00% | 15.00% |
Examples 1 and 2 come from Appendix II of YC's post-money safe user guide. In example 1, YC's table shows the $800k investor at 9.06% because it also buys its pro rata in the round. The 6.56% here is its SAFE shares alone. Example 2 shows the cap turning off. The $8M cap works out to about $0.68 a share, above the $0.6577 round price, so that SAFE converts at the round price and ends up with more than the 10% its cap implied (YC). Example 3 is not a company. The round price is $0.875, both SAFEs convert at $0.70, and the $20M cap never binds.
Why the pool increase lands on founders
YC counts the unissued pool that exists before the round in the SAFE math, and leaves out the increase the round asks for. YC's reasoning: putting the Series A increase in the SAFE math would make founders bear two rounds of hiring dilution by themselves. The lead's term sheet usually puts the increase in the pre-money, so the new money does not pay for it either.
Two levers are left. Size the pool from a hiring plan, not a round number. Size the option pool from a hiring plan walks the seats. Then see who pays for the top-up in the option pool shuffle calculator. Each point of pool you avoid stays with the founders and the SAFE holders.
Cap, discount, or both
YC's standard post-money SAFE has a cap and no discount. YC also posts a discount-only version and an uncapped MFN version. It pulled the cap-and-discount form on 28 August 2021, saying it had not seen cases where that form was the better choice. Carta reports that nearly a third of SAFEs still carry both. A discount only matters when the round prices close to or below the cap. Example 3 shows that case. Carta: 91% of SAFEs on its platform were post-money as of Q2 2026. This tool does not model pre-money SAFEs or uncapped MFN SAFEs.
If you are still choosing the instrument, start with SAFE vs priced round.
Before you sign the next SAFE
SAFE check
- List every SAFE. Amount, cap, discount, and side letters. Include the ones from friends and family.
- Add up amount ÷ cap. That is the percentage you have sold before the round (YC).
- Pick a likely round. Use a pre-money and raise you could defend, plus the pool size the lead will ask for.
- Run it here. Read the founders' line after the round, not the SAFE line.
- Run a down case. Drop the pre-money below your lowest cap and see which SAFEs switch to the round price.
- Check founder vesting terms. A lead can ask you to re-vest at the same close. See founder vesting at a priced round.
- Confirm with counsel. Bring this output and your cap table software export. Not legal or tax advice.
Mistakes
- Reading a SAFE's cap as the company's price. A cap is a ceiling. The round can price below it (YC).
- Treating SAFE ownership as final. YC: the SAFE percentage is post-SAFEs, not post-round. The round dilutes it.
- Leaving the lead's pool increase out of your model. It comes out of founders and SAFE holders.
- Adding a discount to a SAFE that already has a low cap without modeling a down round.
- Counting a pro rata purchase as SAFE ownership. It is new money in the round.
Sources
- Y Combinator, Post-Money Safe User Guide (PDF). Version 1.2, February 2023. Ownership sold = amount ÷ post-money cap; Company Capitalization includes the existing unissued pool and converting securities and excludes the round's pool increase and new money; conversion at the better of Safe Price and round price; cap-and-discount version removed 28 August 2021; Appendix II Example 1 questions 2 and 5 ($200k at $4M, $800k at $8M; $5M at $15M pre; $2.2M at $8.8M pre; 10% pool; founders 51.54% and 55.32%).
- Y Combinator, SAFE financing documents. Current post-money versions: cap no discount, discount no cap, uncapped MFN.
- Carta, Understanding the SAFE. 8 October 2026. Cap and discount definitions; the investor takes the better term; nearly a third of SAFEs carry both a cap and a discount.
- Carta, Pre-money vs. post-money SAFEs. 7 October 2026. Post-money SAFEs do not dilute each other; 91% of SAFEs on Carta were post-money as of Q2 2026.
- VEN (Venture Executive Network). Founder sessions on SAFEs, priced rounds, and founder dilution at Series A, 2026. Session topics only. No closed-session numbers.
SAFE math is easy to skip until the term sheet lands. Founders who have converted a stack of SAFEs at a priced round will pressure-test your caps, pool ask, and round size in a VEN session.