Co-founder Equity Split Calculator
Model fair equity allocations across up to 4 co-founders based on idea, commitment, capital, skills, and risk.
Who conceived the business, technology, or wedge.
Domain expertise, network, technical chops, prior wins.
Full-time effort weighted highest. Part-time scores lower.
Real dollars contributed. Use 0-10 relative to other founders.
What you walked away from (salary, equity, options).
Who conceived the business, technology, or wedge.
Domain expertise, network, technical chops, prior wins.
Full-time effort weighted highest. Part-time scores lower.
Real dollars contributed. Use 0-10 relative to other founders.
What you walked away from (salary, equity, options).
Equity allocation
Equal split would give each founder 50.0%. Deltas show how the weighted model adjusts from that baseline.
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Why the 50/50 default fails most teams
Co-founders almost always start with equal splits because it feels fair, fast, and non-confrontational. Then 18 months later, when one founder has been carrying 70% of the load while the other lost interest, the equal split becomes the source of the breakup - the slow kind, where one person quietly disengages and the cap table never reflects the actual contribution.
The five factors that matter
Different teams weight these differently, but the underlying factors are consistent:
- Idea / IP: Who actually conceived the business, the technology, the wedge. Important early; less important once execution dominates.
- Skills & experience: Domain expertise, network, technical chops, prior wins. Determines speed-of-execution and credibility with investors.
- Commitment / time: The single highest predictor of long-term success. Full-time vs. part-time is a 2-3x weighting difference.
- Capital invested: Real dollars, not notional. Should be priced at a defensible early valuation, not at a 50/50 sweat-equity conflation.
- Risk / opportunity cost: What you walked away from. A founder leaving a $400K/year FAANG job is taking more risk than one leaving an unpaid student gig.
The dynamic equity model (Slicing Pie)
Mike Moyer's “Slicing Pie” framework argues equity should be allocated based on cumulative contributions until the company gets external funding (or starts generating revenue) - at which point the slices freeze. The math is more elaborate than this calculator, but the principle holds: equity should reflect what each founder actually contributed, not a feel-good 50/50.
Vesting protects everyone
Whatever split you land on, **put it on a 4-year vest with a 1-year cliff** at incorporation. This is non-negotiable in any startup raising venture capital, and it protects you from the worst case: a co-founder leaving after 6 months with 30% of the company forever. The cliff means they get nothing if they leave in the first year. The 4-year vest means they earn their full stake by staying.
Have the conversation early
The hardest part of an unequal split isn't the math - it's the conversation. Have it before you incorporate. Write it down. Revisit annually. The cap table you create on day one is the one that will follow you for the next decade, through every funding round, every dilution event, every exit scenario. Get it right at the start.
Frequently asked questions
- Should co-founders always split equity equally?
- No. Equal splits are a heuristic, not a rule. They work when contributions are roughly equal across idea, time, capital, skills, and risk - which is rare. Mismatched contributions with equal equity is the single most common cause of founder breakups within the first 2 years. Use a model that reflects reality, then re-evaluate as roles shift.
- What if one founder is full-time and another is part-time?
- Time commitment is the highest-weighted predictor of long-term success. A part-time co-founder should typically get materially less than a full-time one - often 30-50% less depending on how part-time. Some teams handle this with vesting tied to actually going full-time (no cliff credit until full-time start date).
- What about a founder who invested cash but doesn't work?
- That person is an investor, not a co-founder. Treat cash investment as equity priced at a defensible early valuation - typically $1-3M pre-money for friends-and-family rounds. Don't conflate sweat equity (vests over time) with investor equity (vests immediately).
- Does this calculator handle vesting?
- This shows your initial allocation. Vesting is separate - every co-founder should be on a 4-year vest with 1-year cliff, regardless of equal vs. unequal split. The allocation says 'who gets how much'; the vest says 'over what time and what happens if someone leaves'.
- How many co-founders is too many?
- Three is the empirically best number for venture-scale startups (Y Combinator's data). One founder works for solo-bootstrap. Two is fine. Four or more sharply increases the probability of breakups, alignment problems, and dilution before Series A. If you have 4+ co-founders, consider whether some should be early employees with significantly smaller stakes instead.
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