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SAFE Note

Y Combinator’s standard pre-seed instrument: an investor’s right to convert into equity at the next priced round, with dilution mechanics founders routinely misread.

Concept

Vocabulary that names a phenomenon.

A SAFE is a sale that postpones the count, not a loan that postpones the math. A first-time founder who misses that distinction raises a $1.5M pre-seed on SAFEs at a $10M cap, feels they’ve given away nothing, then learns at the Series A that they sold roughly 15% of the company before the priced round even began. The SAFE did exactly what it was designed to do. Knowing what it does to ownership, and when, separates the founder who knows their cap table from the one who discovers it during diligence.

What It Is

A SAFE — Simple Agreement for Future Equity — is a contract that gives an investor the right to receive equity in a future priced round, in exchange for money paid now. Y Combinator introduced it in 2013 as a deliberately stripped-down alternative to the convertible note. It is not debt: it carries no interest rate, no maturity date, and no obligation to repay. It isn’t equity yet either. It is a promise that converts to shares when a triggering event happens, almost always the company’s first priced equity round.

Two terms do most of the work, and a SAFE can carry one, both, or neither:

  • The valuation cap sets a ceiling on the price at which the SAFE converts. An investor on a $10M-cap SAFE converts as if the company were worth $10M, even if the priced round values it at $30M, so they get three times the shares per dollar that the new round’s investors get.
  • The discount gives the investor a percentage reduction (commonly 10–20%) off the priced round’s per-share price, rewarding them for committing earlier.

When a SAFE has both a cap and a discount, the standard documents convert at whichever produces more shares for the investor, which is usually the cap in a round that priced well above it.

The single most consequential detail is the 2018 revision from a pre-money to a post-money SAFE. The original pre-money SAFE computed the investor’s ownership before counting the other SAFEs in the round, so no investor could know their final percentage until every SAFE had been tallied at conversion. The post-money SAFE fixed the investor’s ownership percentage at signing: a $1M post-money SAFE at a $10M cap buys exactly 10% of the company, measured after all the SAFE money is in but before the new priced round dilutes everyone. This made the instrument legible for investors and is now the market standard. It also shifted dilution decisively onto the founder, because every SAFE’s percentage is now locked and stacks cleanly, and the founder absorbs the sum.

Note

The shorthand “SAFE note” is a misnomer the market uses anyway. A note is a debt instrument; a SAFE is explicitly not one. The phrase persists because the SAFE occupies the slot convertible notes used to fill, and founders search for it under that name.

Why It Matters

The SAFE matters because it is the instrument almost every pre-seed and seed company in the United States now uses, and because its mechanics are the most common place a founder’s intuition about ownership goes wrong. PitchBook and Carta data through 2025 show the post-money SAFE as the dominant early-stage instrument, displacing both priced seed rounds and convertible notes at the earliest stage. A founder who raises on SAFEs without modeling the conversion is not making a small error; they are guessing at how much of their company they still own.

The three readers come at it from different angles. A founder reads the SAFE as speed and simplicity, which it genuinely delivers: a SAFE can close in days on a few-page document with no board approval and no priced-round legal bill, which is why it exists. The hidden cost is that the simplicity hides the dilution until conversion, and the dilution from a stack of uncapped or high-cap SAFEs can be brutal precisely because each one looked small in isolation. An angel investor reads the post-money SAFE as certainty: they know their exact percentage the day they sign, which is the feature the 2018 revision delivered to them. A later-stage investor coming into the priced round reads the SAFE stack as dilution they did not cause but will see on the pro-forma cap table, and they price their own round knowing the founder’s true remaining ownership.

What the concept gives a practitioner is the ability to read a fundraise in terms of ownership rather than cash. “We raised $2M” is a headline. “We sold 18% of the company across four post-money SAFEs that will all convert at the Series A” is the fact, and only the second version tells the founder how much room they have left before they lose control.

How to Recognize a SAFE You Understand

The test of whether a founder actually understands their SAFEs is whether they can state, without opening a model, roughly what percentage of the company is already committed. With post-money SAFEs this is arithmetic, not estimation, and the discipline is to do it continuously rather than at conversion.

The mechanics that decide the outcome:

  • Ownership sold equals investment divided by the cap, for a post-money SAFE. A $500K SAFE at a $10M post-money cap is 5%, full stop, regardless of where the priced round lands. Stacking them is addition: four such SAFEs are 20% before the new round arrives.
  • The cap is the price, not a formality. A SAFE with no cap and only a discount converts near the priced round’s price and dilutes the founder far less; a low cap relative to the eventual round dilutes far more. Founders optimize for a high cap; the dilution math is why.
  • The option pool usually comes out of the founder’s share. When the priced round demands a larger employee option pool, it is typically created pre-money, diluting the founders and SAFE holders but not the new investor. The SAFE conversion and the pool top-up land together at the Series A and compound.
  • Most favored nation and pro-rata clauses change the picture. An MFN clause lets an early investor adopt the better terms of any later SAFE; a pro-rata side letter lets them buy more in the priced round to hold their percentage. Both are common and both belong on the cap table model, not in a drawer.
post-money SAFE ownership = investment / post-money valuation cap

Warning

Modeling SAFEs at their cap and stopping there understates dilution. The full Series A dilution is the converted SAFE percentage plus the new money’s percentage plus the option-pool top-up, and the three compound. A founder who models only the SAFE conversion routinely sees their post-A ownership land several points below their estimate.

How It Plays Out

The instrument’s own history is the clearest case. Y Combinator published the original pre-money SAFE in late 2013, written by Carolynn Levy, to give its companies a faster and cheaper alternative to the convertible note. The note carried interest and a maturity date that could force an awkward conversation if a priced round had not happened in time. Adoption was rapid across the seed market because the document was free, standardized, and short. By 2018 the pre-money version had created a recurring problem: founders raising on a series of pre-money SAFEs could not tell how much they had sold until every SAFE converted at once, and the surprise was reliably unpleasant. YC’s post-money revision, also led by Levy, fixed the investor’s percentage at signing and made the stack legible. It also made it unmistakable, which is the point: the dilution that the pre-money SAFE hid, the post-money SAFE prints on the page.

The quieter version plays out in a founder’s cap table every season. A team raises a pre-seed on a couple of SAFEs at a friendly cap, then adds a few more as the round fills, each one small and each one closed in an afternoon. Eighteen months later, raising a Series A, the founders model the new investor’s 20% and are startled to find their own stake well below where they expected. The SAFE stack converts in full at the same moment, and the option pool the new investor requires comes out of the pre-money. Nothing went wrong with any single SAFE. The error was treating six fast, simple agreements as six separate small events rather than one compounding sale of the company, payable at the Series A. It’s the same instrument working as designed, read wrong.

Consequences

Choosing the SAFE as the pre-seed instrument buys real speed and imposes a real obligation to track what it commits.

Benefits. The SAFE is fast, cheap, and standardized, which lets a founder raise from many small checks without a priced round’s cost or delay, and the post-money form gives investors the ownership certainty that made the instrument bankable. For a company that will clearly reach a priced round, the SAFE defers the expensive valuation negotiation to the moment when the company is worth more and negotiates from a stronger position, which is the right time to have it. The instrument’s ubiquity is its own advantage: every experienced angel and seed fund recognizes the YC documents and will sign them without a fight.

Liabilities. The simplicity that makes the SAFE fast is the same simplicity that lets dilution accumulate unseen, and the founders who are hurt most are the first-timers the instrument was meant to protect. A stack of high-cap or uncapped SAFEs can convert into far more dilution than the founder modeled, and because SAFEs never appear as priced equity until conversion, a cap table that looks clean can hide a large committed sale. The post-money form, for all its clarity, places that full dilution on the founder by design. And a SAFE that never reaches a triggering priced round sits in limbo: with no maturity date, it doesn’t force a conversion, but it doesn’t go away either, which complicates an acquisition or a slow-growing company’s eventual equity event. The SAFE answers how to raise early money quickly. It does not answer whether the founder will still recognize their ownership when the money converts.

  1. Contrasts withConvertible Note
    The convertible note is the debt instrument the SAFE was designed to replace; the SAFE strips out the interest rate and maturity date that define the note.
  2. EnablesCap Table Hygiene
    A clean cap table depends on tracking every SAFE on a fully-diluted, post-conversion basis rather than as a line of cash that has not converted yet.
  3. EnablesRunway
    The capital a SAFE raises is what the runway is built from; the instrument is fast precisely so the cash arrives before the runway closes.
  4. ProducesDilution
    Conversion is the moment a stack of SAFEs becomes equity, and the dilution it creates is the number founders most often underestimate before a priced round.
  5. RelatedLiquidation Preference
    Converted SAFE shares enter the preference stack as preferred stock, so the SAFE's cap quietly determines how much preference the seed investor carries into an exit.
  6. Upstream ofTerm Sheet Mechanics
    The priced round whose term sheet sets the conversion price is the event a SAFE is written to anticipate; the SAFE converts when that term sheet closes.

Sources

  • Y Combinator, the SAFE financing documents and user guide — the primary source for the instrument, including the standard post-money SAFE templates and YC’s own explanation of the cap, discount, and MFN provisions.
  • Carolynn Levy and Y Combinator, the 2018 post-money SAFE announcement and the post-money revision notes — the record of why the pre-money form was replaced and what the post-money form fixes.
  • Carta, cap-table and early-stage financing data — the mechanics of how SAFEs are tracked on a fully-diluted basis and the benchmark data on cap and discount norms through 2025.
  • PitchBook 2025 seed-stage financing reports — the market data establishing the post-money SAFE as the dominant pre-seed and seed instrument, against priced rounds and convertible notes.