Score each founder's contribution from nought to ten, covering time committed, how critical the role is, and money put in. The split is each score as a share of the total. The number matters less than the conversation: co-founder disputes kill more early companies than competitors do, and they are almost always about a discussion nobody had in month one.
Founder share = founder score ÷ sum of all founder scores
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
A visible difference. Say out loud now why it exists, or it will be said for you in month eighteen, at volume, probably over something unrelated.
What the number means
| Distance from an equal split | Reading | What to do about it |
|---|---|---|
| Within 5 points of equal | Healthy | Effectively an equal split, and the evidence rather likes equal splits: they are quick to agree and hard to resent. Add four-year vesting with a one-year cliff and move on. |
| 5 to 15 points from equal | Fragile | A visible difference. Say out loud now why it exists, or it will be said for you in month eighteen, at volume, probably over something unrelated. |
| More than 15 points from equal | Act now | One founder is carrying materially more. That can be perfectly correct, but it needs vesting, written roles and a review date, because the person on the smaller share will re-run this calculation privately for years. |
Worked examples
| Situation | Numbers in | Answer out | Verdict |
|---|---|---|---|
| Two full-time founders, equal roles | 8 and 8 | 50 / 50 | Balanced. Vest it and stop optimising. |
| Full-time builder, part-time domain expert | 9 and 5 | 64 / 36 | Skewed. Defensible, but only if both people can explain it the same way. |
| Founder plus early employee called a co-founder | 10 and 2 | 83 / 17 | Heavily skewed. This is an equity grant with a friendly job title. |
| Three founders, one part-time | 8, 8 and 4 | 40 / 40 / 20 | Skewed, and clearly for a reason. Write the reason down. |
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.
Should co-founders split equity equally?
Usually yes, and the burden of proof sits with anyone arguing otherwise. Noam Wasserman's research on founding teams found that quick, unequal splits agreed before the work was understood correlate with later conflict, mostly because the split was priced off a plan that then changed entirely. Equal splits are simple to defend and cheap to agree. If you genuinely deserve more, vesting and a defined role protect you better than an extra ten percent ever will.
What is founder vesting and why does it matter more than the split?
Vesting means the shares are earned over time, typically four years with a one-year cliff, so a founder who leaves in month five leaves with nothing. It matters more than the split because it fixes the failure mode the split cannot: someone taking a third of the company and a job elsewhere. A fair split without vesting is a promise. An imperfect split with vesting is a structure. Structures survive disagreements; promises do not.
How do you value time versus money in a founder split?
Convert both to the same unit and be explicit about which one is scarcer. Cash invested is usually the easier half to price, since it has a number on it. Full-time work at no salary is the expensive part, and it deserves the heavier weighting because it cannot be recovered or refinanced. A useful sanity check: if this founder left tomorrow, how many months would it cost to replace them? That answer tends to settle arguments faster than an hour of principle.
Put this on your own site
Free to embed, no permission needed, no tracking script smuggled in. The only condition is the credit link that comes with it, which seems a fair trade for the arithmetic.
<iframe src="https://shipfit.ai/calculators/embed/equity-split" width="100%" height="700" style="border:1px solid #e2e8f0;border-radius:16px;" title="Equity split calculator by ShipFit" loading="lazy"></iframe>Use this with
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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.
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ICP (Ideal Customer Profile)
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Frequently asked questions
Should co-founders just split equity equally?
What dimensions should I weigh?
What about vesting?
When should I run this calculator?
Split the equity once you know what you are splitting.
Roles are easier to weigh when the product and the buyer are settled. ShipFit settles both in an afternoon, which is a cheaper way to find out than a cap table.