What is a SAFE note and how does it work?

A SAFE (Simple Agreement for Future Equity) is an investment instrument created by Y Combinator in 2013 as a simpler alternative to convertible notes for early-stage funding. An investor gives a startup cash today, and in return receives the right to convert that investment into equity at a future priced round — usually at a discounted price or capped valuation compared to what new investors pay in that round.

SAFEs have no interest rate and no maturity date, which makes them dramatically simpler than convertible notes. There's no loan to repay if the startup doesn't raise a priced round — the SAFE either converts to equity at a future financing or pays out in a sale or liquidation event (based on whatever conversion price would have applied). This makes SAFEs founder-friendly: no debt clock ticking, no pressure to close a priced round by a deadline.

The two most common SAFE terms are the valuation cap and the discount rate. A valuation cap says: "when this SAFE converts, we get equity at the lesser of the actual round valuation or this cap." For example, if you raise a $1M SAFE with a $8M cap and later raise a Series A at a $20M pre-money valuation, the SAFE converts as if the company was valued at $8M — giving the SAFE investor a much lower effective price per share. A discount rate (say 20%) means the SAFE investor pays 80 cents for every dollar of equity at conversion.

SAFEs now exist in several standard forms: cap only, discount only, cap and discount, and MFN (Most Favored Nation, with no other terms but the right to get the best terms of any future SAFE). The post-money SAFE, introduced by YC in 2018, calculates the investor's ownership on a post-money basis — making dilution more predictable for founders.

The main risk with SAFEs for founders is SAFE stack accumulation. If you raise multiple SAFEs at different caps before a priced round, the amount of dilution at the priced round can be surprising and large. Founders should carefully model out the fully diluted cap table before and after each SAFE to understand what they're committing to.