Free Tool
SAFE Conversion Calculator
See what your post-money SAFEs actually convert to when the priced round arrives. Stack multiple SAFEs, add the round and option pool, and get the full ownership waterfall plus your total dilution.
How post-money SAFE conversion works
The post-money SAFE, the Y Combinator standard since 2018, was designed to make one number unambiguous. Each investor's ownership is the amount invested divided by the post-money valuation cap, fixed at signing. A $500,000 SAFE at a $5 million post-money cap is 10 percent of the company, measured immediately before your next priced round, no matter what else you raise afterward. When that round closes, every SAFE converts into preferred stock at its locked-in percentage, and then the whole pre-round cap table, founders and SAFE holders alike, is diluted by the new investors and by any option pool the term sheet requires. The pool is typically created in the pre-money, the classic option pool shuffle, so it dilutes existing holders rather than the incoming money.
Why stacking SAFEs surprises founders
The certainty that makes each post-money SAFE simple is exactly what makes a stack of them expensive. Because every SAFE's percentage is fixed against a capitalization that already includes the other SAFEs, the holders do not dilute one another. Every point sold comes out of the founders and employees. Founders who mentally track each SAFE in isolation, 10 percent here, another 10, then just 5, discover at conversion that the stack adds up to a quarter of the company before the new round takes its slice. The calculator's default example walks through precisely that trap, and our guide to SAFEs vs. priced rounds covers when the math says to stop signing SAFEs and price the round. A useful guardrail is to keep the combined stack under roughly 20 to 25 percent, which is why the tool flags anything above 20.
A note on pre-money SAFEs and discounts
This calculator models cap-based post-money SAFEs, by far the most common instrument today. Older pre-money SAFEs behave differently: the investor's percentage depends on everything else outstanding at conversion, so the dilution lands differently, as our deck on pre-money vs. post-money SAFEs explains. Discount-only SAFEs and convertible notes, which add interest and maturity dates, also convert on different terms; see convertible notes vs. SAFEs for the comparison.
Model the whole journey
This tool answers one question precisely: what your current SAFE stack costs you at the next round. To model the rounds after that, seed through Series B with option pool top-ups at each step, use our cap table dilution simulator. New to the instrument itself? Start with the SAFE definition in our glossary.
Frequently Asked Questions
- How do I calculate ownership from a post-money SAFE?
- Divide the amount raised by the post-money valuation cap. A $500,000 SAFE at a $5 million post-money cap converts to exactly 10 percent of the company, measured immediately before your next priced round. Locking that percentage in at signing is the defining feature of the post-money SAFE.
- Do post-money SAFE holders dilute each other?
- No. Each post-money SAFE fixes its percentage against a company capitalization that includes every other SAFE, so SAFE investors do not dilute one another. Every new SAFE comes almost entirely out of the founders and employees, which is why stacked SAFEs add up faster than founders expect.
- Does the new option pool dilute SAFE holders?
- Yes, under the standard Y Combinator post-money SAFE. The pool increase adopted in connection with the priced round is excluded from company capitalization, so it dilutes converting SAFE holders and founders pro rata. The new investors are unaffected because the pool is created in the pre-money.
- What is the difference between a pre-money and a post-money SAFE?
- A pre-money SAFE's ownership depends on how many other convertibles are outstanding, so each investor's stake shrinks as more SAFEs are signed. A post-money SAFE fixes the investor's percentage regardless of other SAFEs, shifting all of that dilution onto founders. YC switched its standard form to post-money in 2018.
- How many SAFEs is too many?
- A useful guardrail is to keep combined ownership sold across all outstanding SAFEs under roughly 20 to 25 percent before your first priced round. Because post-money SAFE holders do not dilute each other, every additional SAFE past that point is unusually expensive for founders, and it is time to model pricing the round.
- What happens if the priced round values the company below my SAFE caps?
- A cap-only post-money SAFE still converts at its cap price, which in a down round can be a worse price than new investors pay. This calculator assumes the round prices at or above every cap, the common case; below-cap rounds and discount SAFEs need instrument-level modeling.
Keep learning
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