Co-Founder Equity Split Calculator
Find a fair UK co-founder equity split.
What this calculator does
This co-founder equity split calculator converts contribution into a proposed shareholding. Each founder is scored across four factors — the idea, capital contributed, time committed, and relevant experience — and the calculator applies weights to produce a contribution score and the equity share it implies.
The default weighting puts time at 40 percent, capital at 30, with idea and experience at 15 each. That distribution reflects a widely held view: what a founder gives up and does over several years matters more than what they brought to the first conversation. The weights are adjustable, and arguing about them is itself a productive exercise.
When to use it
Use it in the first few months of working together, once roles have settled but before outside investment arrives. Splitting equity on day one means guessing; splitting it after a funding round means renegotiating in front of an investor, which is uncomfortable for everyone involved.
Its real value is in structuring an awkward conversation. Scoring each factor separately converts a vague feeling that the split is unfair into a specific disagreement about commitment or capital, which can actually be resolved. If the founders cannot agree on the scores, that tells you something important about the partnership while it is still early.
Understanding the inputs
Score each founder on each factor using a consistent scale, and do it independently before comparing notes. Idea covers who originated the concept and the underlying insight. Capital is money actually invested or personally guaranteed, not money promised at some future point.
Time is the most consequential input and should reflect commitment across the expected period rather than this particular week — full time versus evenings and weekends is the distinction that matters. Experience means directly relevant domain knowledge, industry relationships, and prior operating experience, not general seniority. Adjust the weights if your circumstances differ, but agree them before scoring rather than after seeing the result.
How is this calculated?
Weighted Score per founder = (Idea × 20%) + (Capital × 30% normalized) + (Time × 50%). Equity % = Score / Total Scores.
A worked example
Two founders score out of ten. Founder A: idea 9, capital 2, time 10, experience 5, giving a weighted score of 67. Founder B: idea 3, capital 8, time 6, experience 9, giving 66. The split lands at roughly 50.4 percent to A and 49.6 to B — close enough that a straight 50-50 with proper vesting is entirely defensible.
Change one variable: B commits full time, scoring 10 on time. B's score rises to 82 against A's 67, shifting the split to about 55-45 in B's favour. A single factor moved the outcome by ten points, which is the clearest possible argument for making equity vest against sustained commitment rather than fixing it permanently at the outset.
Limitations and assumptions
The output is a discussion tool and nothing more. It cannot weigh the particular relationships, technical skill, or risk appetite that make one founder genuinely irreplaceable, and it treats the factors as independent when they interact — capital from a founder with no other income counts for more than the same sum from a wealthy one.
It also assumes contributions can be judged accurately at the start, which they cannot. Roles change, commitment shifts, and one founder's input often proves decisive in ways nobody foresaw. That is exactly why vesting matters more than the opening percentage. Whatever you agree, have a solicitor put it into a shareholders' agreement with four-year vesting, a one-year cliff, leaver provisions, and IP assignment.
Common Questions
- Should co-founders simply split equity equally?
- Equal splits are common and avoid the resentment that comes from haggling, but they only work where contributions are genuinely comparable. Where one founder is full time and another part time, or one funds the company alone, an equal split breeds its own resentment — usually a year or two later, when unwinding it is far harder.
- Why is time weighted more heavily than the idea?
- Because ideas are plentiful and execution is not. A founder who leaves a salaried job and works two years unpaid takes far more risk and contributes far more value than one who supplied the concept and advises at weekends. Most frameworks weight full-time commitment at around 40 percent for that reason.
- How do I value cash against sweat equity?
- Convert unpaid work into cash at market salary and treat it as equivalent. A founder forgoing £70,000 a year for two years has contributed £140,000, comparable to a co-founder investing £140,000. That reframing usually settles the argument faster than any abstract debate about percentages ever will.
- What is vesting and does every founding team need it?
- Vesting means earning shares over time, typically four years with a one-year cliff, so a founder leaving in month eleven takes nothing. In the UK this is usually implemented through leaver provisions in the articles and a shareholders' agreement. Without it, an early departure leaves a large dead stake that makes the company unfundable.
- Do founder shares need to be a single class?
- Not necessarily, but keep it simple early on. Multiple classes with different rights complicate SEIS and EIS eligibility, since qualifying investment must generally be in ordinary shares carrying no preferential rights. Growth shares and alphabet shares have legitimate uses, but introducing them before a first round often creates avoidable problems.
- What about share options for early employees?
- An EMI scheme is the standard UK route and is highly tax-efficient for qualifying companies and employees. Set aside a pool of roughly 10 to 15 percent before your first funding round, since investors will require one anyway and creating it afterwards typically dilutes founders alone rather than everyone.
- Should the CEO hold more equity?
- Sometimes, and a few points of differential for the role is common. A large gap justified purely by title ages badly, though, because titles change and the share register does not. Weight the substantive contributions — commitment, capital, expertise — rather than where someone sits on the organisation chart.
- When should we formalise the split?
- Early, but not on the first day. Wait until roles have become clear, usually a few weeks or months in, then document it properly with a shareholders' agreement, leaver provisions, and IP assignment. Leaving it until after the first outside investment makes the conversation considerably more difficult.
- How binding is a calculator like this?
- Not at all. It is a structured way of surfacing disagreement about what each person is contributing, which is the conversation that genuinely matters. Treat the output as a starting point, then have a solicitor draft what you agree, including vesting, leaver provisions, and assignment of intellectual property.