Fundraising · YC Deal Mechanics
The YC SAFE, explained — the post-money agreement every YC founder signs.
The SAFE (Simple Agreement for Future Equity) is the contract Y Combinator wrote in 2013 to replace convertible notes and standardized in 2018 as the post-money SAFE. This is what it actually is, how the math works, and the traps founders miss.
What a SAFE actually is
A SAFE is not debt. It's not equity yet either. It's a promise: the investor gives you money today, and in exchange gets the right to shares at your next priced round, an acquisition, or an IPO. There is no interest, no maturity date, and (unlike a convertible note) no legal obligation to ever repay if the company shuts down without a triggering event.
The document is short — six pages of legal text you can actually read. YC publishes the templates for free at ycombinator.com/documents. Every YC founder signs a slightly customized version of the post-money SAFE.
Post-money vs pre-money — the shift that changed everything
The original 2013 SAFE was pre-money. Ownership got calculated before new money came in, which meant every subsequent SAFE diluted the earlier SAFE investors. Nobody knew their real ownership until conversion. Cap tables became unreadable.
YC's 2018 post-money SAFE fixed the ownership percentage at the moment of conversion. If a $10M-cap SAFE puts in $500K, that investor owns exactly 5% at conversion — no matter how many SAFEs you sold after. Cleaner for investors, more diluting for founders. This is the version YC uses today.
The YC standard deal, in SAFE terms
YC invests $125,000 for 7% on a post-money SAFE at a $1.79M post-money valuation. Then a separate uncapped MFN SAFE covers the additional $375,000. The MFN means: whatever cap and discount your next SAFE round carries, YC's $375K auto-adjusts to those same terms.
Do the math: a founder raising a $10M-cap seed after YC will effectively give YC ~10.75% total for the full $500K, before the seed round's new dilution.
Traps founders miss
- Stacking uncapped MFNs. If you sell three uncapped MFN SAFEs and then one $8M-cap SAFE, all three uncapped SAFEs snap to the $8M cap. Model this before you close.
- Pro-rata rights. YC's SAFE side-letter includes a pro-rata right at the Series A. Don't forget to model this at Series B.
- Option pool refresh. Post-money SAFEs don't protect against a Series A pool refresh — that dilution hits founders and SAFE holders equally.
- Signing before incorporating. SAFEs require a Delaware C-corp. Founders who sign before flipping their LLC create a cleanup mess.
FAQ
What is a YC SAFE?
A SAFE (Simple Agreement for Future Equity) is the investment contract Y Combinator invented in 2013 to replace convertible notes. It gives an investor the right to shares in a future priced round, without setting a valuation today. YC uses the post-money SAFE — the version they standardized in 2018 — for every company they fund.
What's the difference between pre-money and post-money SAFE?
A post-money SAFE fixes the investor's ownership percentage at the moment of conversion, before the next round's new money dilutes them. A pre-money SAFE (the 2013 version) gets diluted by every subsequent SAFE. Post-money is simpler math, more predictable dilution for investors, and heavier dilution for founders — which is why every YC company signs one.
How does the YC standard deal use SAFEs?
YC invests $125,000 for 7% on a post-money SAFE, plus an uncapped MFN SAFE for the additional $375,000. Both convert at your next priced round. See our full YC deal breakdown for the exact cap table math.
What is the valuation cap on a SAFE?
The valuation cap is the maximum company valuation at which a SAFE converts into equity. If you raise a Series A at a $50M pre-money valuation but a SAFE has a $10M cap, the SAFE converts as if the company was worth $10M — giving that investor more shares. Caps are the single most negotiated SAFE term.
What is an MFN clause in a SAFE?
Most Favored Nation. If you sell later SAFEs on better terms (a lower cap, a discount), the MFN investor gets to swap into those better terms. YC's $375K SAFE is uncapped with an MFN — meaning YC's terms auto-improve to match whatever your next SAFE round looks like.
Do SAFEs count as debt?
No. SAFEs are not loans, they don't accrue interest, and they don't have a maturity date. They convert only when a triggering event happens (a priced round, an acquisition, or an IPO). This is the single biggest legal difference between a SAFE and a convertible note.
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