YC's post-money SAFE changes founder dilution in a way few calculate

Y Combinator maintains a page dedicated to the SAFE (Simple Agreement for Future Equity) documents, the instrument it created in 2013 through attorney Carolynn Levy and which, according to YC itself, has already been used to raise more than US$15 billion across portfolio companies. The text is lean and practical, but it hides a business decision that the Brazilian founder usually makes without doing the math: when raising from an American investor, they almost always migrate from the local convertible note to the post-money SAFE, and the two dilute differently.

The point that matters to decision-makers isn't the form. It's that the SAFE, in the version that became YC's standard in 2018, stops being 'convertible just like ours' and becomes a contract that fixes, at the moment of signing, the exact percentage the founder is selling.

What Post-Money Solved (and for Whom)

The insight behind post-money is ownership transparency. By YC's own definition, in a SAFE with a post-money valuation cap, the stake sold is the invested amount divided by the cap. Period. It doesn't depend on how much comes in during the later priced round, and it doesn't depend on any last-minute math.

The source's example is straightforward: targeting US$1 million in funding and willing to sell 15%, the post-money cap is US$1M ÷ 15% = ~US$6.7M (or ~US$5.7M pre-money). Raising less on the same cap sells less:

| Raised | Post-money cap | Ownership sold | |---|---|---| | US$500k | US$6.7M | ~7.5% | | US$800k | US$6.7M | ~12% | | US$1M | US$6.7M | ~15% |

It seems obvious, but that clarity is precisely the difference. Under the old pre-money SAFE, and under the typical Brazilian convertible note, the founder only found out the real dilution when the Series A round closed, adding up all the convertibles, stacking them with the new check, and recalculating the price per share. Post-money removes that uncertainty from the investor and shifts it entirely onto the founder: every signed SAFE is already a defined slice of the cap table.

Where the Brazilian Founder Gets Tangled Up

The technical note that almost no one reads in YC's guide: the post-money cap is 'post' all the money raised across SAFEs, not just that one SAFE, and it's 'post' the options and the option pool existing before the priced round. But it is not post the money from the equity round that comes afterward, nor the pool increase made in that round.

What this means in practice, as an editorial reading: if the founder issues several post-money SAFEs at different times, each one locks in its percentage separately and they add up. Selling 7.5% in one SAFE today and another 6% in a different one three months from now isn't 'roughly 13% that gets adjusted in the round.' It's 13.5% already committed, regardless of what happens to the Series A valuation. The post-money SAFE doesn't protect the founder against their own stacked fundraising: whoever carries all the dilution from the previous SAFEs is the founder, not the new investors in the priced round.

YC itself explains this when discussing the MFN (Most Favored Nation), the SAFE with no cap and no discount that automatically adopts the best terms of any SAFE issued afterward. The source's recommendation is surgical: close and receive the wire for the lower-cap SAFEs before issuing an uncapped MFN, because the date the MFN uses is the later of signing or receiving the money. It's the kind of sequencing detail that changes who ends up with which slice, and one that the Brazilian convertible note never forces you to think about.

Convertible Note vs. SAFE: Not the Same Thing in Translation

The instinct of anyone who has already raised money in Brazil is to treat the SAFE as 'their version of the convertible note.' It isn't. The SAFE, by YC's own definition, is not debt: it carries no interest, has no maturity date, and only converts into stock when a priced round happens. The convertible note, compared on the same page, is debt with accruing interest and a deadline for repayment or forced conversion.

The Brazilian convertible note resembles the convertible note more closely: it's a loan agreement (mútuo) with adjustment and a term, which brings the accounting and tax implications of debt until it converts. The SAFE eliminates that, but at the cost of locking in ownership too early for anyone who hasn't done the math.

• Conversion trigger: in the post-money SAFE there's no minimum round size to trigger conversion; any equity financing converts it. In the mútuo, the trigger is usually negotiated.
• Liquidity and dissolution: in an acquisition or IPO, the SAFE investor with a cap receives the greater of 1x their money back or conversion into common stock. In a shutdown, they get their invested amount back, and the SAFE ranks junior to debt, as non-participating preferred.
• Accreditation: the SAFE investor must be accredited; if they aren't by the round's closing date, the company can rescind the agreement and return the money.

The New Operational Detail: SAFEs via AI Agent

The page includes an addition that signals where the process is headed: 'Send a SAFE,' the official, free tool, is now programmatic and 'agent-friendly.' There's a ready-made prompt to install the YC CLI (curl -fsSL https://bookface.ycombinator.com/cli/install.sh | bash), authenticate, and run commands like yc safes create, yc safes update , and yc safes send .

YC itself issues the warning that any founder should take seriously:

Sending a SAFE triggers an email to a real investor and cannot be undone. Never run yc safes send without first showing the exact terms and obtaining explicit confirmation.

Useful, but the strategic message is the opposite of comfort: automating the issuance of an instrument that locks in dilution in minutes increases the risk of stacking SAFEs without seeing the total sold. Signing speed doesn't replace doing the cap table math.

When the SAFE Isn't Worth It Here

The tool's SAFE only supports companies incorporated in the US, and YC offers separate forms for Canada, Cayman, and Singapore, always with the caveat to consult local counsel. For the Brazilian startup that's still 100% a Ltda in Brazil, with no offshore structure, the pure American SAFE doesn't apply without a corporate layer (typically a flip to Delaware or Cayman) that carries its own cost and tax implications.

In other words: adopting the SAFE isn't just switching contracts, it's signing up for a regime that presupposes a vehicle abroad. For anyone who isn't raising from an American investor or doing a flip, the local convertible note remains cheaper and more aligned with the tax reality.

For anyone building a tech business in Brazil, the implication is a single one: before signing any post-money SAFE, add up on paper every SAFE you plan to issue, apply investment ÷ cap to each one, and look at the accumulated percentage as if the Series A had already happened. The founder's dilution shortfall is rarely in the first check. It's in the math he didn't do for the second, the third, and the option pool that comes along with it. YC's official calculator is on the same page, and it's the first place to run these numbers before the agent runs send.