Weighs each cofounder's contribution across time committed, role, and capital invested — then returns a recommended equity split plus a fairness check that flags suspicious 50/50 defaults. Use this before incorporation, before the founder agreement gets signed. Once the cap table is locked, this calculator suggests fair splits but can't unwind a bad one.
Your numbers
Weighted contribution 0-10. Time (full-time vs part-time) + role criticality + capital. 0 = not a co-founder.
The verdict
2 co-founders
Mildly skewed. Within 15% of equal. Talk explicitly about the difference now or it surfaces as resentment in month 18.
How this is calculated
Each founder gets a single weighted contribution score from 0-10, intended to fold three real dimensions into one number:
- Time — full-time vs part-time, weighted heaviest (equity follows risk, and the founder who quits the day job is taking the biggest risk).
- Capital — how much each founder is putting in.
- Role criticality — CEO and CTO usually count more than other roles at month 0-12, but this collapses as the team grows.
Equity % = founder_score / sum_of_scores × 100. Proportional, no horse-trading.
The verdict thresholds (within 5% / 15% of equal) come from Noam Wasserman's Founder's Dilemmas data showing splits more than 15% from the founder-perceived "fair" point predict cap-table renegotiation within 24 months.
What this doesn't tell you
- Whether your co-founders agree with the scores. The calc is only fair if the scoring conversation already happened. If you score yourself an 8 and your co-founder scores you a 5, the calc surfaces a problem, not a solution.
- What happens at dilution. Series A typically dilutes founders 20%. The split percentages today are the split percentages forever — adjusted only by who gets the larger employee-pool refresh.
- Whether to vest. Always do. The calc gives the target; vesting is the mechanism. 4-year vest, 1-year cliff, accelerated on acquisition is the modern default.
Use this with
7 Powers
The 7 Powers framework names every defensible advantage a business can have. If you can't pick one for your startup, you're betting on a fair fight.
Idea Validation
Most founders confuse idea validation with idea-receiving-encouragement. The two have nothing in common. Here's what real validation looks like, and the four methods that actually produce it.
Should I start a startup?
Five honest questions. (1) Are you ok losing 12-24 months of income? (2) Do you have a specific problem you keep coming back to, or is the appeal generic? (3) Can you handle being wrong publicly for 6+ months? (4) Do you have one validated idea (not just enthusiasm)? (5) Are you doing this because you want to OR because you think you should? Yes to 4-5: probably worth starting. Yes to 0-2: not yet, and that's fine. Most successful founders said yes to all five before quitting.
Frequently asked questions
Should co-founders just split equity equally?
What dimensions should I weigh?
What about vesting?
When should I run this calculator?
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