What Is a SAFE Note? SAFE vs Convertible Note With Real Numbers
What a SAFE note is, how a post-money SAFE converts, how it differs from a convertible note, worked examples with real numbers, and when founders should use each.
By Onward ScoutPublished 6 min read
In short: a SAFE (Simple Agreement for Future Equity) is a short contract in which an investor gives you money now for the right to shares later, when you raise a priced round. It is not debt. A convertible note works similarly but is a loan with interest and a maturity date. For most early rounds, a post-money SAFE is the simpler choice.
What is a SAFE note?
In short
A SAFE is a contract that converts an investor's money into shares at your next priced equity round, usually at a price set by a valuation cap. It has no interest, no maturity date and no repayment obligation. "SAFE note" is a nickname; it is not actually a note.
Y Combinator, which created the instrument, describes it as a short contract an investor signs to fund your startup now in exchange for the right to shares later, converting automatically at a priced round[Y Combinator]. It was created at YC in 2013 and has been used to raise over $15B for YC portfolio companies[Y Combinator]. Its spread beyond YC has been just as striking.
What is the difference between a SAFE and a convertible note?
In short
Both convert into equity later, but a convertible note is debt: it accrues interest and has a maturity date by which it must be repaid or converted. A SAFE is not debt, so it has no interest or deadline, which makes it simpler, faster and cheaper to sign.
| SAFE (post-money) | Convertible note | |
|---|---|---|
| Legal form | Contract for future equity | Debt (a loan) |
| Interest | None | Yes, accrues until conversion |
| Maturity date | None | Yes, repay or convert by a date |
| Ownership clarity | Amount ÷ cap, known at signing | Depends on interest and timing |
| Typical use | Pre-seed and seed rounds | Bridges, some regions and investors |
| Paperwork | One short standard form | Longer, more negotiated |
YC's own comparison puts it plainly: a convertible note is debt with accruing interest and a maturity date for repayment or forced conversion[Y Combinator], while a SAFE has neither. That maturity date is the practical difference: if you have not raised by then, note holders can push for repayment or renegotiation at the worst possible moment.
How common are SAFEs compared with convertible notes?
In short
SAFEs now dominate the earliest rounds. On Carta's platform, they made up 90% of pre-seed rounds in early 2025, with convertible notes a small and shrinking share that included some large deals.
Carta's data for the first quarter of 2025 shows SAFEs accounted for a record 90% of all pre-seed rounds on its platform, with convertible notes making up the other 10%[Carta, Q1 2025]. Measured by dollars rather than deals, the SAFE share was 82% of pre-seed capital[Carta, Q1 2025], suggesting a few large rounds still used notes.
How does a post-money SAFE convert? A worked example
In short
With a post-money SAFE, the investor's ownership at conversion is the amount divided by the post-money cap: $500,000 on a $10M cap is 5%. When the priced round happens, that 5% is diluted by the new investors and any new option pool, just like the founders' stake.
Work it through with real numbers:
- The SAFE. An investor puts in $500,000 on a $10M post-money cap. Their stake at conversion: $500,000 ÷ $10,000,000 = 5%.
- The seed round. You raise $2.5M at a $12M pre-money valuation. New investors own $2.5M ÷ $14.5M ≈ 17.2%.
- After the round. The new money and any option pool created in the round dilute the SAFE. With a 10% pool in the pre-money, the SAFE holder's 5% becomes 5% × (1 − 17.2% − 10%) ≈ 3.6%, and founders end at roughly 69.1%.
- The same money as a convertible note. Had the investor lent the $500,000 as a note at 8% simple interest instead, converting a year later in the same seed round at the SAFE's price per share, $540,000 of principal and interest would convert instead of $500,000: 8% more shares, about 5.4% before the new money instead of 5%, and about 3.9% after the round instead of 3.6%.
YC explains why founders like this structure: the biggest advantage of the post-money SAFE is that the amount of ownership sold is immediately transparent and calculable for both founder and investor[Y Combinator]. Run your own numbers in the cap table calculator.
How do you choose a valuation cap?
In short
Work backwards from two numbers: how much you want to raise and how much of the company you are willing to sell. Raising $1M for 10% implies a $10M post-money cap. Then check that the cap is defensible against your traction and comparable rounds.
YC's guidance takes the same approach: start from how much you're targeting and how much ownership you're willing to sell and the valuation cap follows from the two[Y Combinator]. This keeps you focused on dilution, which is permanent, rather than on the headline valuation, which is not.
A useful discipline is to set a dilution budget for the whole pre-seed stage, for example 15% to 20% across every SAFE you sign, and to cap each new SAFE so the total stays inside it. Founders who skip this step often discover at the seed round that four small SAFEs added up to far more than they intended.
What should founders watch out for with SAFEs?
In short
Stacking several SAFEs without modeling the total, side letters that add rights you did not plan for, MFN clauses that reprice earlier SAFEs, and treating a SAFE as free money. Each SAFE is a promise of ownership; track them all in one cap table.
- Stacking. Every post-money SAFE comes out of the founders' share, not out of earlier SAFE holders'. Model the cumulative effect before each new signature.
- Side letters. Pro rata rights, information rights or board observer seats are often added in side letters. They may be reasonable; just make sure you know what you have granted.
- MFN surprises. If you have MFN SAFEs outstanding and later issue a SAFE with a lower cap, the MFN holders can take that lower cap.
- No board seat, but real ownership. SAFE holders usually have no vote until conversion, which can make it easy to forget they will soon be shareholders.
How do investors view SAFEs versus notes?
In short
Most early-stage investors now accept post-money SAFEs as standard, which is why they dominate pre-seed rounds. Some prefer notes for the debt protections, especially in bridges or where they worry about the company never raising a priced round.
The trade-off is protection versus simplicity. Note holders get interest and a maturity date that gives them leverage if things go slowly; SAFE holders accept less protection in exchange for a standard, quick document. If an investor asks for a note, it is worth asking why; the answer tells you what they are worried about.
What about uncapped and MFN SAFEs?
In short
An uncapped SAFE has no valuation cap; it converts at the next round's price, sometimes with a discount. A most-favored-nation (MFN) SAFE adopts better terms that later SAFEs receive. Both are less common, but you will meet them in accelerator deals.
Y Combinator's standard deal uses one. It invests $375,000 on an uncapped MFN SAFE alongside $125,000 for a fixed 7%; if your next SAFEs carry a $15M post-money cap, the MFN SAFE converts to 2.5% of the company on YC's own worked example[Y Combinator deal]. MFN terms are founder-friendly early on but can surprise you if you later issue a low-cap SAFE.
When should you use a convertible note instead?
In short
When an investor insists on debt protections, when local law or tax treatment favors notes, or for a short bridge between priced rounds where a maturity date and interest are acceptable. Otherwise, the SAFE's simplicity usually wins.
A typical case for a note: a company that raised a seed round eighteen months ago needs six more months of runway before its Series A, and existing investors agree to a $750,000 bridge with modest interest and a twelve-month maturity. The debt terms reflect a short, defined gap; for an open-ended first raise, a SAFE is usually cleaner.
Whichever you choose, keep a running model of every instrument you sign. Stacking several SAFEs at different caps is the most common way founders lose track of their ownership. Before you raise, read the pre-money vs post-money guide, and if an accelerator offer is on the table, compare it with our accelerator vs incubator guide. This article explains common terms and is not legal or tax advice; have a lawyer review your documents.
Frequently asked questions
What does SAFE stand for?
Simple Agreement for Future Equity. It is a short contract created at Y Combinator in 2013 that converts an investment into shares at a later priced round.
Is a SAFE note debt?
No. A SAFE has no interest and no maturity date, and it is not a loan. "SAFE note" is a common nickname, but the instrument is not a note.
What is a valuation cap on a SAFE?
The maximum valuation at which the SAFE converts. With a post-money cap, the investor's ownership at conversion is roughly the amount invested divided by the cap.
What happens to a SAFE if the company never raises a priced round?
It depends on the terms. Standard SAFEs pay out or convert in a sale of the company and return money in a dissolution only after creditors; there is no repayment date as with a note.
Should I use a discount or a cap on my SAFE?
Most post-money SAFEs today use a valuation cap and no discount. A discount alone gives investors less certainty about their ownership.
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