Founder Equity Split Calculator

Split founder equity on contribution, not gut feeling

The default 50/50 handshake is the most common source of co-founder conflict. This founder equity split calculator uses a weighted scoring model instead: you decide how much each contribution factor matters — idea, capital, commitment, skills and risk — then score every founder from 0 to 10 on each one. Each founder's weighted points are added up, and their equity percentage is simply their share of the total points. The result updates live as you type, and every number stays on your device.

Why weighted factors work

Ideas are cheap; execution and sustained commitment are expensive — which is why the default weights lean toward commitment (30) and skills (25) rather than the original idea (10). But every startup is different: if one founder is writing a large check, raise the capital weight; if someone is quitting a secure job while others stay employed, raise risk. Because the weights are fully editable, the model bends to your situation instead of forcing a formula on you. The score breakdown under each result shows exactly how every percentage was earned, which makes the negotiation transparent rather than emotional. Estimates only, not professional, financial, tax or legal advice; have a lawyer paper any final split and consider vesting.

How to use it

1. Set the five factor weights to reflect what matters most in your startup — or keep the sensible defaults.
2. Rename the two starting founders and score each factor 0–10 (0 = no contribution, 10 = exceptional).
3. Click + Add founder for a third or fourth co-founder, or ✕ to remove a row.
4. Read each founder's live percentage and the weighted-point breakdown, then adjust scores until the split feels defensible to everyone.

FAQ

Do the weights have to add up to 100?

No. Only the relative sizes matter — weights of 10/15/30/25/20 give the same split as 2/3/6/5/4. Use whatever scale is easiest to reason about.

Why don't the rounded shares always total exactly 100%?

Each share is rounded to one decimal for display, so the sum can land at 99.9% or 100.1%. The tool shows the rounded total so you can nudge the final cap table by hand.

Should equity ever be exactly equal?

It can be — if the scores genuinely come out even. The value of this exercise is that an equal split becomes a conclusion you reached together, not a default you avoided discussing.

Is my data uploaded anywhere?

No. The calculator is plain JavaScript running entirely in your browser; names and scores never leave your device.