A SAFE (Simple Agreement for Future Equity) is a financing instrument developed by Y Combinator that gives investors the right to receive equity in a future priced round. Unlike convertible notes, SAFEs are not debt — they have no interest rate or maturity date. The post-money SAFE (introduced in 2018) is now the standard, but it significantly changes dilution math for founders.
What Is a SAFE?
A SAFE is a contractual right to receive equity in a future priced financing round. The investor gives the company money today. In exchange, the company promises to issue shares to the investor when it raises a priced round (or in certain other liquidity events). SAFEs were designed to be simpler than convertible notes: no interest, no maturity date, no debt. They are a single, standardized document (available free from Y Combinator's website).
Pre-Money vs. Post-Money SAFEs
Y Combinator introduced the post-money SAFE in 2018. The difference is significant:
Pre-money SAFE (pre-2018): The cap is applied to the pre-money valuation of the next round. Multiple SAFEs dilute each other — the ownership percentage of each SAFE investor is not fixed until the priced round.
Post-money SAFE (2018+): The cap is applied to the post-money valuation (including all SAFEs). Each SAFE investor's ownership percentage is fixed at the time of investment.
Why it matters: With post-money SAFEs, founders can calculate exactly how much dilution each SAFE causes at the time of signing. With pre-money SAFEs, dilution is uncertain until the priced round.
Example:
- Company raises $1M on a $10M post-money cap SAFE
- Investor owns exactly 10% ($1M ÷ $10M) — fixed at signing
- Additional SAFEs dilute the founders, not the SAFE investor
Key SAFE Terms
Valuation Cap: Same concept as convertible notes — the maximum valuation at which the SAFE converts.
Discount Rate: Gives SAFE holders the right to convert at a discount to the next round price.
MFN (Most Favored Nation): Gives the investor the right to adopt the terms of any future SAFE if those terms are more favorable.
Pro-Rata Rights: The right to participate in future financing rounds to maintain ownership percentage.
SAFE Conversion Mechanics
At a priced round:
- Calculate the SAFE conversion price: lower of (a) cap price or (b) discounted price
- Divide SAFE amount by conversion price = shares issued
Common Founder Mistakes
- Not modeling SAFE dilution before signing — stacked SAFEs can cause shocking Series A dilution
- Mixing pre-money and post-money SAFEs — creates complex, unpredictable dilution math
- Ignoring pro-rata rights — can constrain future round allocation
- Setting caps too low — a low cap can create excessive dilution at Series A
Key Takeaways
- SAFEs are not debt — no interest, no maturity date.
- Post-money SAFEs (2018+) fix investor ownership at signing — simpler and more transparent.
- Model SAFE dilution before signing — stacked SAFEs can cause significant Series A dilution.
- MFN and pro-rata rights are important secondary terms to negotiate.
- Y Combinator's SAFE documents are free and widely accepted as the standard.
Filed under M&A, Partnering & Due Diligence. Working session: Calendly.
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