Tools · Founder equity
Founder equity split calculator
Score each founder 0–10 on six factors, weight the factors, and see what the arithmetic says. It is a conversation starter, not an answer — the output is only as good as the scores you type.
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Founders
Weights and scores
Set a weight for each factor — any positive numbers, they get normalised to sum to 100%. Then score each founder 0–10. Argue about the scores. That argument is the point.
| Factor | Weight | Founder 1 | Founder 2 |
|---|---|---|---|
| IdeaWho brought the original insight, and how much of it survived contact with a real customer. | 5.0% | ||
| CommitmentHours committed from here forward — full-time, part-time, or nights and weekends. | 20.0% | ||
| CapitalCash already in, or firmly committed, and whether it is genuinely at risk. | 15.0% | ||
| ExpertiseDomain knowledge, technical depth, or relationships the company could not easily hire. | 15.0% | ||
| RiskWhat each founder gave up — salary, a visa, a competing offer, a stable job. | 20.0% | ||
| RoleResponsibility going forward — who owns revenue, product, hiring, and the board relationship. | 25.0% |
Read this before you use the number
- A 55/45 that took a week to negotiate is usually worse than a 50/50 agreed in an hour with four-year vesting and a one-year cliff. The negotiation costs more than the four points.
- This output is an artefact of the scores you typed. Two honest founders will score the same facts differently, and both will be able to defend their numbers. The value is in the argument the tool forces, not in the percentage it prints.
- Past contribution is a weak predictor of future contribution. Equity pays for the next several years, not for the last six months.
- Unvested equity is the actual protection. If a co-founder leaves in month eight, what matters is the vesting schedule, not whether they were allocated 48% or 52%.
Suggested split
Weighted score 5.00 / 10 · 0.0 points vs an equal split
Where that came from
- Idea5.0% × 5 = 0.25 pts (5% of their score)
- Commitment20.0% × 5 = 1.00 pts (20% of their score)
- Capital15.0% × 5 = 0.75 pts (15% of their score)
- Expertise15.0% × 5 = 0.75 pts (15% of their score)
- Risk20.0% × 5 = 1.00 pts (20% of their score)
- Role25.0% × 5 = 1.25 pts (25% of their score)
Weighted score 5.00 / 10 · 0.0 points vs an equal split
Where that came from
- Idea5.0% × 5 = 0.25 pts (5% of their score)
- Commitment20.0% × 5 = 1.00 pts (20% of their score)
- Capital15.0% × 5 = 0.75 pts (15% of their score)
- Expertise15.0% × 5 = 0.75 pts (15% of their score)
- Risk20.0% × 5 = 1.00 pts (20% of their score)
- Role25.0% × 5 = 1.25 pts (25% of their score)
- Equal split
- 50.0%
- Spread
- 0.0 pts
- Furthest from equal
- 0.0 pts
Nobody is more than five points from an equal split. That is inside the noise of how you happened to score things. Take the equal split, put the time into the vesting terms, and stop.
How this is calculated
There is no proprietary formula here. Five steps, all of them visible:
- Normalise the weights. Add up the six weights and divide each one by that total, so they sum to 1. With the default weights (5, 20, 15, 15, 20, 25) role carries 0.25 and idea carries 0.05.
- Score each founder from 0 to 10 on each factor.
- Weighted score = the sum of (normalised weight × score) across the six factors. The maximum is 10.
- Percentage = a founder's weighted score ÷ the sum of every founder's weighted score × 100. Two founders on 6.0 and 4.0 get 60% and 40%.
- Round by largest remainder. Percentages are converted to tenths of a point, everyone gets the floor, and the leftover tenths go to whoever has the biggest fractional remainder. That is why three equal founders show 33.3 / 33.3 / 33.4 rather than three numbers that add up to 99.9.
What each factor is actually measuring
Each factor has a way it usually goes wrong. Read the third column before you argue about the second.
| Factor | Default weight | What it measures | Common failure mode |
|---|---|---|---|
| Idea | 5 | Who brought the original insight, and how much of it survived contact with a real customer. | Overpaid. An idea is worth very little before someone builds it, and the founder who had it usually argues otherwise. |
| Commitment | 20 | Hours committed from here forward — full-time, part-time, or nights and weekends. | Scored on intent rather than hours. Score what they will actually do next year, not what they say they will do. |
| Capital | 15 | Cash already in, or firmly committed, and whether it is genuinely at risk. | Cash conflated with equity. Money in is usually better priced as a note or an investment than as a bigger founder slice. |
| Expertise | 15 | Domain knowledge, technical depth, or relationships the company could not easily hire. | Everyone rates their own discipline highest. Ask what you would have to buy if this person walked out today. |
| Risk | 20 | What each founder gave up — salary, a visa, a competing offer, a stable job. | Measured in absolute dollars, which flatters whoever had the highest previous salary rather than whoever risked the most. |
| Role | 25 | Responsibility going forward — who owns revenue, product, hiring, and the board relationship. | Titles scored instead of accountability. Score the decisions each person will be judged on. |
How to split founder equity without wrecking the company
Most founder equity arguments are not really about the numbers. They are about whether each founder believes the others will still be working as hard in three years. A calculator cannot settle that, and this one does not try. What it can do is force the conversation into named categories, so that instead of arguing about fairness in the abstract you argue about whether commitment should carry more weight than capital.
Then be suspicious of the answer. Every input on this page is a judgement someone typed. Score the same six factors on a different afternoon and the split moves. If the result lands within a few points of equal, the honest reading is that the tool found no real difference and the precision is fake. Take the equal split. If it lands somewhere lopsided, treat that as a prompt to check whether the scores are ones everybody would repeat in front of each other, not as a licence to hand someone 62%.
The deeper problem is that equity buys the future and this calculator mostly measures the past. Whoever wrote the first prototype has a strong case today and may be the person who leaves in month nine. Whoever joined last with no code and no cash may end up carrying the company. You cannot fix that with a better formula. You fix it with vesting.
Vesting is the part that actually protects you
Four-year vesting with a one-year cliff is the common convention for founder stock. Founders hold their shares from day one, but the company keeps a right to repurchase the unvested portion if they leave, and that right lapses on a schedule.
What a cliff does
Nothing vests before the cliff date. Leave the day before it and you keep nothing. On the cliff date the whole accrued tranche vests at once, and from then on vesting continues in monthly or quarterly increments until the schedule completes. The cliff exists so that a co-founder who leaves early walks away with nothing rather than with a permanent slice of a company they are no longer building. Run the schedule on the vesting calculator.
Acceleration
Single-trigger acceleration vests some or all of the unvested shares on a change of control by itself. Double-trigger requires two events: a change of control and, usually within a defined window afterwards, the founder being terminated without cause or resigning for good reason. The mechanics matter to an acquirer, who is buying the team as well as the company, so this is a term to settle with counsel rather than a default to copy.
The 83(b) question
Restricted stock that is subject to vesting raises a section 83(b) election question: whether to be taxed on the value at grant, when the shares are usually worth very little, instead of as each tranche vests and the value may be far higher. The election is made by filing a written statement — or Form 15620 — with the IRS, and it cannot be revoked without IRS consent. The filing window is short and statutory. Confirm the exact deadline, and whether the election is right for you at all, with a CPA before you sign anything. Source: IRS, Update to the 2024 Publication 525 for section 83(b) election (accessed 2026-08-11).
This page is general information, not legal, tax, or financial advice. Founder equity, vesting, and tax elections are jurisdiction-specific and fact-specific. Talk to a lawyer and a CPA before you commit to anything here.