Startup Financing Tool

SAFE dilution calculator

A YC post-money SAFE tells you the investor’s ownership directly: at conversion the investor receives the investment divided by the post-money valuation cap of the company. Because every post-money SAFE measures its slice against the same post-money base, the slices add up — and each new SAFE is carved out of the founders’ ownership, not out of the earlier investors’ fixed percentages. This tool shows that running total as you stack SAFEs.

It is the companion to our practice note, Which YC SAFE should I use?

Your SAFEs

Enter the investment amount and the post-money valuation cap for each SAFE you have issued. Add a row for every SAFE in the stack.

SAFE 1
SAFE 2

What converts, and what founders keep

  • ≈ 5%= $500,000 ÷ $10,000,000
  • ≈ 4%= $500,000 ÷ $12,500,000
SAFEs convert to
9%
Founders and existing holders keep
91%

Every SAFE you add is carved out of the founders’ stake — not out of an earlier investor’s fixed percentage. That is the “what you see is what you get” design of the post-money SAFE.

What this does and does not model

This is illustrative arithmetic, not legal or financial advice, and not a substitute for a modeled cap table from your counsel. To keep the math transparent, it makes a few deliberate simplifications:

  • Post-money valuation-cap SAFEs only. It does not model discount-only or MFN SAFEs, or the “better of cap or discount” comparison.
  • It assumes the cap binds — that the eventual priced round values the company above each cap, so the cap sets the conversion. This is the standard worst-case-dilution snapshot.
  • It stops at the SAFEs. It does not add the dilution from the priced round’s new money or any new option-pool top-up created at that round — those dilute founders and SAFE investors alike and are a later modeling step.

YC’s own standard deal is a good illustration of that first limit: it pairs a fixed-7% post-money SAFE (mechanically a ~$1.79M implied cap) with a $375,000 uncapped MFN SAFE. That uncapped piece has no cap to convert against until the company sets one elsewhere, so it is exactly the case this calculator leaves out.

For the full picture of how these instruments work, read Which YC SAFE should I use?