What is a post-money SAFE conversion calculator?

A post-money SAFE conversion calculator models what happens to your cap table when every outstanding SAFE note converts into preferred equity at a priced round. Because post-money SAFEs lock in an ownership percentage at signing, the math compounds across multiple SAFEs — and founder dilution from SAFEs is only fully visible when the Series A prices. This tool runs the full iterative dilution math for you, including MFN propagation, cap vs discount arbitration, and option pool refresh.

Post-money vs pre-money SAFE: which one dilutes founders more?

Post-money SAFEs give the investor a fixed percentage of the fully diluted cap table post-conversion. Pre-money SAFEs give a percentage of the company pre-new-money — so when additional SAFEs are signed, existing SAFE investors get diluted alongside the founders. Post-money SAFEs shift more dilution onto founders because subsequent SAFEs do not dilute prior SAFE holders. Most YC founders underestimate this by 3–5 percentage points.

How SAFE notes convert at a priced round

At the priced round, each SAFE converts at the better (for the investor) of two prices: the valuation cap divided by the fully diluted share count, or the priced round's price-per-share discounted by the SAFE's discount rate. The calculator computes both prices and picks the lower one, which is the binding constraint. For post-money SAFEs, the cap denominator includes new-money shares; for pre-money SAFEs, it excludes them. That single denominator choice can shift founder ownership by 2–4 percentage points.

YC SAFE MFN clauses: propagation rules explained

A Most Favored Nation (MFN) clause lets an earlier SAFE investor inherit the best terms of any later SAFE the company signs — typically the lowest valuation cap and highest discount. The tool's MFN engine sorts every SAFE by signed date, then for each MFN holder scans all later SAFEs and rewrites the cap/discount to the most favorable combination found. When MFN triggers, the original cap effectively disappears, often causing a silent re-price that founders don't see coming. The gold MFN badge on a SAFE card shows you exactly when this has happened.

Valuation caps and discounts: how the calculator picks the winner

When a SAFE has both a valuation cap and a discount, the investor gets the better price. The valuation cap converts to a fixed price per share at conversion, while the discount always sits relative to the round price. If the round prices above the cap, the cap binds ("cap triggered"). If the round prices below the cap but still above the discounted price, the discount binds. If neither price beats the round price, the SAFE simply converts at round price — that's "neither / tied." The per-SAFE card shows you which constraint was active and the effective discount captured.

Iterative dilution: why multiple pre-money SAFEs need a solver

Pre-money SAFEs are circular: SAFE A's share count depends on the total fully diluted share count, which itself includes SAFE B's share count, which depends on the total — and so on. There's no closed-form solution. The calculator uses fixed-point iteration with a convergence threshold of 0.00005%; most stacks converge in 3–6 iterations. For post-money-only stacks convergence is usually 1–2 iterations because post-money SAFEs do not dilute each other. The solver reports iteration count as a trust signal so you can see when your stack is a math trap.

Modeling your SAFE stack before a Series A

Founders raising on SAFEs should stress-test the stack 60–90 days before starting Series A negotiations. Drop in the current SAFE stack, add a hypothetical priced round (pre-money valuation, investment amount, pool refresh size and timing), and check where founder ownership lands. If it's below 50%, consider raising less, cutting the pool expansion, or pushing pre-money higher. The dilution curve chart above shows you exactly how much pre-money valuation you need to keep founders above target.

Option pool shuffle: who really pays for the post-round pool?

When investors require a pool refresh pre-money, the pool is sized using the pre-money share count — which means only founders and earlier investors get diluted. When the pool is sized post-money, new-money investors share the dilution proportionally. The calculator lets you flip between pre-money and post-money pool timing so you can see who actually pays. The founder difference is typically 1.5–3 percentage points and it's a core negotiation lever most founders miss entirely.

Reading the SAFE cap calculator output: founder % and triggered-by

The hero number is founder ownership post-conversion — the single most important output. The per-SAFE cards tell you which constraint (cap or discount) priced each SAFE; ideally you want most SAFEs to hit their cap, because that means the cap is doing its job. The 6-dim report card grades your stack on Founder Dilution, SAFE Mix Health, Cap Effectiveness, Discount Value, Pool Refresh Pain, and Round Readiness. An A-level composite score means you're board-ready; a D means you need to restructure before pricing.