SAFE Conversion Calculator

The formulas

Post-money SAFE (YC, 2018+). Per the Y Combinator Post-Money Safe User Guide, the SAFE's ownership is fixed at purchase amount ÷ post-money valuation cap, measured against the "Company Capitalization" immediately before the priced round. That capitalization includes all shares, issued options, the existing unissued pool and all SAFEs and notes converting, but not the new money or the pool increase made for the round. So:

Safe Price = Post-Money Valuation Cap ÷ Company Capitalization
Discount Price = Standard Preferred Price × (1 − discount)
Conversion price = lower of the two (whichever applies)

Example (YC guide logic): $1M on a $10M post-money cap = 10% of the company immediately before the Series A, regardless of other SAFEs. Those other SAFEs dilute the founders, not this SAFE.

Pre-money SAFE (legacy). Safe Price = Pre-Money Cap ÷ capitalization excluding SAFEs. Multiple pre-money SAFEs dilute each other.

Priced round. Price per share = Pre-money ÷ (pre-round fully diluted shares + pool top-up + SAFE conversion shares). Because SAFE shares and the pool top-up depend on the price, the calculator solves this circular system numerically.

Post-money vs pre-money SAFE: what is the difference?

With a post-money SAFE the investor knows exactly what percentage they own before the priced round; each new SAFE dilutes only the founders and existing holders. With a pre-money SAFE, SAFE holders dilute each other and the percentage is unknown until the round.

Cap or discount: which applies?

The SAFE holder gets whichever produces the lower price per share (more shares). A cap usually wins when the round valuation is well above the cap.

What does MFN mean?

"Most favoured nation": an uncapped, undiscounted SAFE whose holder may adopt better terms given in later SAFEs before the round. Here an MFN SAFE (with no cap/discount entered) adopts the lowest cap and highest discount among SAFEs listed after it.

Why does the option pool top-up matter?

New investors usually require the pool increase to be in the pre-money ("option pool shuffle"), so it dilutes founders and SAFE holders but not the new money. Under the post-money SAFE, the pool increase is excluded from Company Capitalization, so the SAFE's cap price is unaffected, but its final post-round percentage is diluted.

Simplifications

Fractional shares are not rounded; pro rata rights, convertible notes with interest, "Standard" vs "Shadow" preferred and liquidity/dissolution events are not modelled.