How to Split Equity Between Cofounders

Equity splits break friendships. They end companies. They create lawsuits that drag on for years.

And yet most cofounders spend more time choosing a company name than figuring out how to divide ownership. They pick 50/50 because it is easy, shake hands, and move on. Then two years later, when one person is working 70 hours a week and the other has quietly checked out, that handshake becomes a grenade.

The equity conversation is uncomfortable. That is exactly why you need to have it properly, early, and with clear thinking.

This guide covers how to approach the split, what factors actually matter, and how to structure the conversation so both cofounders walk away feeling good about the outcome.

TL;DR

• 50/50 is not always fair. Equal is easy, not necessarily right
• The conversation matters more than the formula. How you discuss it reveals how you will handle future conflict
• Factors that matter: time already invested, role criticality, opportunity cost, experience gap
• Factors that do not matter: who had the original idea
• Use vesting in any multi-founder setup. Treat no-vesting as an exception you have to justify
• Write it down. A verbal agreement is not an agreement

Why This Conversation Is Hard

Talking about equity means talking about value. And talking about value means one person might have to say: "I think I am worth more than you."

That feels brutal. So cofounders avoid it. They default to equal splits because it feels fair, democratic, and avoids awkwardness.

But equal is not the same as fair. And avoiding awkwardness now creates much bigger problems later.

The founders who handle this well treat it as a test. If you cannot have an honest, slightly uncomfortable conversation about equity, how will you handle the much harder conversations coming later? Firing someone. Pivoting the product. Running out of money. Taking a down round.

The equity conversation is practice for everything else.

When to Have the Conversation

As early as possible. Ideally before major work is done together, and definitely before money is raised.

Once you have been working together for months, the conversation becomes harder. One person has built the product. Another has been talking to customers. Both feel ownership. Untangling contributions retroactively is a mess.

If you have already incorporated or started building, you have not failed. But have the conversation now, before the stakes get higher. The longer you wait, the harder it gets.

The Myth of the Idea

Here is something that kills equity conversations: "But it was my idea."

A raw idea, the shower thought, the napkin sketch is worth almost nothing. Execution is worth almost everything.

But there is a difference between a raw idea and a validated concept. If someone spent six months talking to customers, building a prototype, validating the market, and developing relationships before bringing on a cofounder, that is not "just an idea." That is early work, and it has value.

The distinction matters. "I thought of this first" deserves nothing extra. "I spent six months proving this could work" deserves recognition.

If someone insists they deserve 70% because they had the original thought, that is a red flag. If they deserve more because they did real work before you joined, that is a legitimate conversation.

Factors That Actually Matter

There is no formula that removes the conversation. But there are factors worth weighing:

Time already invested

Has one founder been working on this for six months while the other just joined? Prior work matters. Someone who validated the market, built a prototype, and talked to 50 customers has already contributed. That should be reflected.

Commitment level going forward

Is everyone full-time? If one founder is keeping their job for six months while the other goes all-in, that difference in risk and commitment should affect the split.

Role criticality

For a deep-tech company, the technical founder might be irreplaceable. For a sales-driven business, the commercial founder might be the critical piece. Whose skills are hardest to replace if they left tomorrow?

Opportunity cost

Is one founder leaving a £200K job while the other is fresh out of university? The person taking a bigger financial hit is taking more risk. That risk has value.

Experience gap

A second-time founder who has raised before, built teams, and learned from failure brings pattern recognition that a first-time founder does not have. That experience is worth something.

Capital contribution

Is one founder putting in £50K of savings? Cash matters, though less than you might think. Sweat equity is usually more valuable in the long run.

Factors That Do Not Matter

Who had the idea. Already covered. Ideas are cheap.

Who is CEO. Title alone does not determine ownership. That said, the CEO role often comes with heavier accountability, investor relationships, and final decision rights. If one founder is clearly taking on that burden, it might factor into the conversation. But do not assume CEO automatically means more equity.

Who is older. Age is irrelevant.

Who has more followers on LinkedIn. Seriously, this comes up. It should not.

The Framework

There is no perfect formula. But here is a framework to structure the conversation:

Start with equal, then adjust.

Begin by assuming 50/50. Then ask: is there a clear reason to deviate?

If both founders are starting at the same time, going full-time together, with comparable skills and similar opportunity cost, equal is probably right.

If there are real differences in contribution, commitment, or risk, adjust from there.

Small gaps are not worth fighting over.

The difference between 50/50 and 52/48 is not meaningful. Do not create resentment over 2%.

If the gap is real, make it meaningful. 60/40 or 55/45 says "we acknowledge a difference." 51/49 says "we could not have the real conversation."

Both people need to feel good.

A split that one person secretly resents will poison the company. The goal is not to win the negotiation. The goal is a split that both founders genuinely believe is fair, even if it required compromise.

If you cannot reach that point, you might not be the right cofounders for each other.

Common Scenarios

These are starting points for conversation, not formulas. Every situation is different, and the right answer depends on context you will have to figure out together.

Two founders, same start date, both full-time, similar skills

50/50 is probably right. Do not overthink it.

One founder started six months earlier, built MVP, validated market

The early founder has earned something for that work. 55/45 or 60/40 in their favor is reasonable, depending on how much progress they made.

Technical founder builds everything, business founder does sales

Usually equal or close to it. Both roles are critical. The technical founder builds the product; the business founder builds the revenue. Neither works without the other.

One founder is part-time for six months

Adjust the split to reflect the commitment difference, or use a vesting schedule that accounts for when each founder goes full-time.

One founder has done this before and has investor relationships

Experience has value, but so does hunger. A 55/45 or 60/40 split might be fair, but do not overweight experience. The first-time founder grinding 80 hours a week might end up contributing more.

Joining a Company Already in Motion

What if you are not starting together? What if someone built something for 6-12 months and now wants you to join as a cofounder?

This is a different conversation. The existing founder has already taken risk, done work, and created something. You are joining something in progress, not building from zero together.

Typical ranges when joining an existing early-stage company:

• Joining pre-product, pre-revenue: 20-40% is reasonable
• Joining with MVP and early users: 15-30% is reasonable
• Joining with revenue or funding already raised: 10-20% is reasonable

These ranges depend heavily on what you bring. A technical cofounder joining a business founder who cannot build anything might command the higher end. A generalist joining a company with a working product and traction might be at the lower end.

The key question: how critical are you to what happens next? If the company cannot succeed without you, that is worth more. If you are an accelerant but not essential, that is worth less.

Do not compare your equity to what the original founder has. Compare it to what is fair given when you are joining and what you are contributing from this point forward.

Vesting: The Non-Negotiable (Almost)

Whatever split you agree on, it means little without vesting.

Vesting makes equity conditional on time. If someone leaves after three months, they do not walk away with their full stake.

Standard terms: four years, one-year cliff.

This protects everyone. The founder who stays builds the company and earns their equity. The founder who leaves does not take half the cap table for three months of work.

In any multi-founder setup, and in any company taking outside money, vesting should be the default. Treat no-vesting as an exception you have to justify, not the other way around.

If a cofounder resists vesting, that tells you something. They want the upside without committing to the timeline. That is not a partner you want.

For the full mechanics of how vesting works, read founder vesting explained.

Write It Down

A handshake is not an agreement. A verbal commitment is not enforceable.

Once you agree on the split:

• Incorporate properly
• Issue shares according to the split
• Sign stock purchase agreements
• File your 83(b) elections (if in the US)
• Put vesting terms in writing

This is not bureaucracy. This is how you avoid spending £50K on lawyers two years from now arguing about who owns what.

If you cannot afford a lawyer, use a service like SeedLegals or Clerky. The cost is minimal compared to the cost of getting it wrong.

When the Conversation Goes Wrong

Sometimes you cannot agree. One person wants 60%, the other thinks 50/50 is fair, and neither will move.

This is information. If you cannot align on equity, you probably cannot align on the hundred harder decisions coming later.

Better to discover this now than after you have raised money, hired people, and built something together.

Walking away from a cofounder relationship before it starts is painful. Walking away two years in is catastrophic.

After the Split

Once equity is divided, let it go.

Do not relitigate the split every time one person has a big win or the other has a slow month. The split is done. Focus on building the company.

If circumstances change dramatically (one founder goes part-time, someone new joins as a third cofounder), you might need to revisit. But those should be rare exceptions, not ongoing negotiations.

Where to Go From Here

Understanding equity basics? Read startup equity explained

Setting up vesting? Read founder vesting explained

Managing your cap table? Read cap table basics

Closing Thought

The equity split is not about math. It is about the relationship.

Two founders who can have an honest, slightly uncomfortable conversation about value, contribution, and fairness will probably survive the harder conversations ahead.

Two founders who avoid the conversation, default to equal because it is easy, and hope it all works out are building on a shaky foundation.

Have the conversation. Be honest. Be generous. And write it down.

The best cofounder relationships are the ones where both people feel like they got a fair deal. Not because they won the negotiation, but because they built something together that they both believe in.

That starts with getting the equity right.