What is a SAFE?
A SAFE (Simple Agreement for Future Equity), introduced by Y Combinator in 2013, is an instrument early-stage startups use to raise capital quickly and cheaply. The investor gives money today; in return they don't get shares immediately but a right that converts into equity at the next priced round. That way, neither side has to negotiate the company's valuation today.
A SAFE is not debt — it carries no interest, no maturity date, and is never repaid. That's what separates it from a convertible note. Because of its simplicity, a Pre-Seed round can close in days with low legal cost, which is what made the SAFE the de facto standard of the pre-seed stage.
How a SAFE works: cap, discount, and MFN
A SAFE's economics are set by two core terms: the valuation cap and the discount. The valuation cap sets the maximum valuation the investor will use at conversion — if the company reaches a higher valuation at the next round, the early investor still converts at the lower cap, capturing a larger share as the reward for their early risk.
The discount gives the SAFE investor a percentage reduction (typically 10-20%) against the next round's price. If a SAFE carries both a cap and a discount, conversion uses whichever is more favorable to the investor — the one that yields more shares. An MFN (Most Favored Nation) clause means that if a later SAFE is signed on better terms, the early investor is upgraded to those terms.
Valuation cap vs discount: the difference, with an example
Say an investor puts in $100K on a SAFE with a $5M valuation cap. The company then closes its next round at a $10M pre-money valuation. The investor converts not at $10M but at the $5M cap — meaning their money buys shares at half the price the later investors paid. That's the concrete reward for going in early.
On a SAFE with only a 20% discount and no cap, the same investor buys at the $10M round's price minus 20% — a far weaker advantage than the cap gives. This is why most early-stage investors prioritize the valuation cap, which is what actually protects them against valuation uncertainty.
Post-money SAFE or pre-money SAFE?
In 2018, Y Combinator moved the SAFE from pre-money to post-money, and that created a critical difference for founders. In a post-money SAFE, the valuation cap represents the company's value after all SAFEs are included — so how much of the company the investor gets is nearly certain at signing. For the investor that means transparency; for the founder it means the dilution from each stacked SAFE comes directly out of the founder.
The critical consequence: in post-money SAFEs, dilution is not shared among the SAFEs; each new SAFE only dilutes the founders and prior holders. So if you're raising on multiple SAFEs, you have to model their combined conversion at the priced round at the moment you sign each one — otherwise you'll hit your seed round with a far more diluted cap table than you expected.
When SAFEs convert, and the dilution surprise
A SAFE converts to equity not on the day it's signed but at the next priced round (usually seed). That's exactly where the problem begins: founders often collect several SAFEs back to back ("$200K at this cap, $150K at that cap") and treat each one as a small, separate transaction. But when the seed round arrives, all of those SAFEs convert at once, and the total dilution comes out far larger than any single one suggested.
The only way to avoid this surprise is to model each SAFE, on the day you sign it, together with its conversion at the priced round. The free dilution calculator on this site shows how a round dilutes founder ownership, and our post 'Startup Dilution Explained' walks step by step through how the option pool adds to that picture and why it costs more than its headline number.
SAFE vs convertible note vs priced round
SAFEs, convertible notes, and priced rounds all raise capital, but at different speeds and complexity. A priced round sets a valuation today, issues shares immediately, and requires the most legal work; it generally suits seed and beyond. A convertible note is debt — it carries interest and a maturity date — and is more complex than a SAFE.
The SAFE is the simplest and fastest option: it isn't debt, it defers valuation, and it's ideal for Pre-Seed. Its cost is the invisibility of dilution; because signing is easy, founders often don't clearly see how much equity they've committed until the priced round arrives. Simplicity is an advantage, but it demands disciplined tracking.
Testing SAFE and round decisions in the simulation
Founder Runway runs a 20-turn arc from Pre-Seed to Series A and shows the cap-table effect of early capital decisions in real time, alongside cash and investor trust. Raise aggressively on a low cap early in a run, then watch where founder ownership lands at the seed round — feel the compounding effect of SAFE conversion by playing it, not in theory.
It's the fastest way to feel whether a round bought you runway or quietly bought away your ownership — without paying for the lesson with a real cap table.
Conclusion
A SAFE is an instrument that closes a Pre-Seed round quickly and cheaply by deferring valuation; its economics are set by the valuation cap and the discount. But in post-2018 post-money SAFEs, each new SAFE dilutes only the founders, and the conversion stays invisible until the priced round. Model every SAFE with its conversion at signing. The free dilution calculator on this site shows how the round you raise affects founder ownership in seconds.
Frequently asked questions
What is a SAFE?
A SAFE (Simple Agreement for Future Equity) is an early-stage instrument, originated by Y Combinator, in which an investor gives money today in exchange for a right that converts into equity at the next priced round. It is not debt — no interest, no maturity — and by deferring the valuation negotiation it lets Pre-Seed rounds close fast.
What's the difference between a valuation cap and a discount?
The valuation cap fixes the maximum valuation the SAFE investor uses at conversion; if the company is valued higher at the next round, the investor still converts at the lower cap. The discount gives a percentage reduction (typically 10-20%) against the next round's price. If both are present, conversion uses whichever favors the investor.
When does a SAFE convert into equity?
A SAFE converts not on the day it's signed but at the next priced round (usually seed), joining that round's dilution via its cap or discount. Because multiple stacked SAFEs all convert at once, the total dilution can be larger than any single one suggested when viewed alone.
What's the difference between a post-money and a pre-money SAFE?
In 2018 YC moved the SAFE to post-money: in a post-money SAFE the cap represents the company's value after all SAFEs are included, so the investor's share is clear at signing. The cost to founders is that each new SAFE's dilution falls only on founders and prior holders and is not shared with later SAFEs.
Is a SAFE, a convertible note, or a priced round better?
A SAFE is the simplest and fastest, isn't debt, and is ideal for Pre-Seed; its cost is that dilution stays invisible. A convertible note is debt (with interest and a maturity date) and more complex. A priced round sets a valuation today and issues shares immediately, requires the most legal work, and generally suits seed and beyond.
Test this decision in the game.
Apply the same assumption across one run; which metric burned three turns later?