Cofounder Equity Split Calculator
Rate each founder across seven contribution dimensions on a 0 to 10 scale. The calculator weights the inputs and recommends an equity split with vesting guidance.
Who brought the original concept, market insight, or unique angle. Ideas are cheap, but the founder with the deepest customer insight gets credit here.
Are they full-time from day one or moonlighting until traction. Full-time founders take more personal risk and should get more equity.
Money they are putting in directly or absorbing as foregone salary. This is the most quantifiable input.
Who is actually shipping the product, owning the codebase, and making architectural decisions in year one.
Customer development, fundraising, go-to-market, hiring, and operational infrastructure.
Existing relationships with target customers, investors, hiring pipeline, or strategic partners.
What they are walking away from. A senior engineer leaving a $400K job takes more risk than a recent grad.
Who brought the original concept, market insight, or unique angle. Ideas are cheap, but the founder with the deepest customer insight gets credit here.
Are they full-time from day one or moonlighting until traction. Full-time founders take more personal risk and should get more equity.
Money they are putting in directly or absorbing as foregone salary. This is the most quantifiable input.
Who is actually shipping the product, owning the codebase, and making architectural decisions in year one.
Customer development, fundraising, go-to-market, hiring, and operational infrastructure.
Existing relationships with target customers, investors, hiring pipeline, or strategic partners.
What they are walking away from. A senior engineer leaving a $400K job takes more risk than a recent grad.
The model shows contributions within 5 percentage points across founders. A clean even split is defensible. Still implement four-year vesting with a one-year cliff.
Vesting checklist
- ✓Four-year vesting schedule. Equity vests in equal monthly increments over 48 months. This is the Silicon Valley standard and what every seed investor will require.
- ✓One-year cliff. Nothing vests until the first anniversary. A cofounder who leaves before month 12 walks away with zero equity. This is critical protection.
- ✓Single trigger acceleration on termination without cause. If a cofounder is fired without cause, accelerate 6 to 12 months of remaining vesting.
- ✓Double trigger acceleration on acquisition. If the company is acquired and the cofounder is terminated within 12 months, accelerate full vesting.
- ✓83(b) election filed within 30 days. US founders must file this with the IRS to lock in the low strike price for tax purposes.
- ✓Cofounder agreement signed before product or revenue. Get this done within 60 to 90 days of starting work together, not after traction.
- ✓Reserve 10 to 15 percent for option pool. You will need this for the first 5 to 10 employees. Reserve it before fundraising or investors will require it from the founders.
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Frequently asked questions
Should cofounders split equity 50/50?+
A clean 50/50 split is the most common default and works well when founders contribute roughly equally across all dimensions. However, it is rarely the right answer. Studies from Noam Wasserman at Harvard Business School show that teams who split equity too quickly often regret it. The deeper the conversation about contributions, risk, and full-time commitment, the better the long-term partnership. If one founder is bringing the idea, working full-time, and putting in cash while the other is part-time, a 60/40 or 70/30 split is more honest and usually creates less resentment over time.
How much equity should a technical cofounder get?+
Technical cofounders typically receive 30 to 50 percent of total founder equity when they join at the earliest stage and build the product. The lower end (30 to 40 percent) applies when the business cofounder originated the idea, brought capital, and has strong customer access. The upper end (40 to 50 percent) applies when the technical cofounder is full-time from day one, the product itself is the moat, and there is no pre-existing business asset. For software MVPs in 2026, technical execution is usually the most leverage-creating role in year one.
When should founders sign the equity agreement?+
Founders should sign a formal cofounder agreement within 60 to 90 days of starting to work together, before any meaningful product or revenue exists. Equity should always be subject to a four-year vesting schedule with a one-year cliff. This means a cofounder who leaves after six months gets zero equity, and a cofounder who leaves after two years keeps half of their grant. Vesting protects the company if a cofounder departs and is non-negotiable from sophisticated investors at the seed stage.
What is a one-year cliff in cofounder vesting?+
A one-year cliff means a cofounder must stay with the company for at least one full year before any equity vests. If they leave or are terminated before the one-year mark, they forfeit their entire equity grant back to the company. After the cliff, the remaining equity vests in equal monthly increments over the next 36 months. This structure is standard in Silicon Valley and protects the company from giving away significant ownership to a cofounder who departs early without meaningful contribution.
How does dilution affect cofounder equity over time?+
Founder equity gets diluted with every funding round. A typical path: founders start with 100% combined, give up 10 to 20% to a seed round, another 15 to 25% at Series A, another 15 to 20% at Series B, and so on. After two to three rounds, founders collectively own 30 to 50 percent of the company. Employee stock option pools (usually 10 to 15 percent) also dilute founders. The percentage split between cofounders stays constant, but the absolute ownership shrinks. This is why the initial split matters less than the relative ratio: a 60/40 split stays 60/40 in proportional terms even after dilution.
Can cofounder equity be changed later?+
Technically yes, but it is painful and rarely done well. Renegotiating equity after the fact requires unanimous founder agreement, board approval if you have one, and triggers tax implications for the receiving founder. The cleanest mechanism is to use vesting acceleration or additional grants tied to specific milestones (rather than reshuffling existing equity). The much better answer is to get the initial split right by having an honest conversation upfront about commitment, contribution, and risk before any equity is granted.
What happens if a cofounder wants to leave?+
If a cofounder leaves before the one-year cliff, they forfeit all unvested equity. If they leave after vesting has started, they keep whatever has vested but lose the rest. The company typically retains a right of first refusal to buy back their vested shares at fair market value if the cofounder ever tries to sell. This is why the cofounder agreement should explicitly cover departure scenarios: voluntary resignation, termination for cause, termination without cause, death, and disability. Each scenario can have different treatment of vested equity.