SAFE conversion calculator.

How a post-money SAFE converts

Y Combinator's post-money SAFE converts automatically at the initial closing of an equity financing. In the valuation-cap form, the SAFE becomes the greater of two share counts: the Purchase Amount divided by the lowest price per share of the new Standard Preferred Stock, or the Purchase Amount divided by the Safe Price, which is the Post-Money Valuation Cap divided by the Company Capitalization. Company Capitalization is measured just before the financing and counts all issued shares, options and promised options, the unissued option pool, and all converting securities, including this SAFE (which is why it is called post-money). In the discount form, the SAFE converts at the lowest price per share of the new stock multiplied by the Discount Rate, where the Discount Rate is 100 minus the discount, as a percent.

Because the SAFE is counted in its own denominator, its ownership is simply purchase amount / cap of that capitalization. YC's own example: a $1M raise at 15% ownership sold is a post-money cap of $1M / 15%, about $6.7M. This calculator solves the share count algebraically: SAFE shares = existing shares x (amount / cap) / (1 - amount / cap).

If you enter both a cap and a discount, the calculator gives the SAFE whichever produces more shares. YC publishes the cap, discount and MFN forms as separate documents, so a cap-plus-discount SAFE is a negotiated variation. Check your signed document.

Worked example

Amount $500,000, cap $5,000,000, 8,000,000 shares, round pre-money $10,000,000 including the SAFE shares, $2,000,000 of new money. SAFE share of capitalization = 500,000 / 5,000,000 = 10%, so SAFE shares = 8,000,000 x 0.10 / 0.90 = 888,889 and the Safe Price is $0.5625. The round price is $10,000,000 / (8,000,000 + 888,889) = $1.1250, so the new investors buy 1,777,778 shares and own 16.67%. The SAFE holds 8.33% after the round and existing holders 75.00%. With a $20,000,000 cap and a 20% discount instead, the discount wins: 533,333 shares at $0.9375.

Limits

This models one SAFE. Other SAFEs and notes converting in the same round change the Company Capitalization, and so every SAFE's share count; so does a new option pool increase, which the YC form counts only to the extent of promised options. The calculator assumes the round's pre-money valuation includes the SAFE shares, a common way to price a round but not the only one. Pro rata rights, MFN terms and Liquidity or Dissolution Events are outside this model.

Sources, opened 8 October 2026: Y Combinator, Post-Money Safe, Valuation Cap Only (Section 1(a) and Section 2 definitions of Safe Price and Company Capitalization); Y Combinator, Post-Money Safe, Discount Only (Discount Price and Discount Rate); Y Combinator, The SAFE: the standard way startups raise money (the $1M at 15% example).