How to Split Equity Between Co-Founders: A Fair Framework

A common way to split equity between co-founders is to start from an equal split among the people who are essential and working full time, move off equal only for a lasting reason you can write in one sentence, and put every founder, the CEO included, on four-year vesting with a one-year cliff. Almost all of the work is still ahead of you, so in our view equity should pay for that work.

Definition: A co-founder equity split is the percentage of a startup's initial common stock that each founder buys at formation, usually subject to vesting so that the company can repurchase unvested shares if a founder leaves.

Most split fights are about the past. The equity is about the future.

Vesting, more than a lopsided split, is what protects the company if someone leaves. And the market appears to be moving toward equal splits anyway. Carta reported in June 2026 that 44.6 percent of two-founder teams that formed companies on its platform in 2025 split equity equally, up from 34.5 percent for teams formed in 2016, and that the median two-founder split was 51 to 49.

Start equal and make every gap earn its place

Here's how we see it: every true co-founder starts with the same number, and any deviation needs a reason that will still be true in year three. Four ideas sit behind that view. Reasonable founders weigh them differently.

1. Ideas are cheap; execution is scarce. Accelerators and funds see the same ideas again and again. Having the idea first is rarely a strong reason for a 90 to 10 split. And if the founders can't agree on a split at all, treat that as a warning about trust or commitment on the team, not a negotiating problem to solve with a spreadsheet.

2. You're paying for the future, not the past. A company worth building takes most of a decade. A few months of head start, a domain name or a prototype says little about who will create the value in years two through ten. We think of equity as pay for work not yet done.

3. Investors read the split as a signal. A 10 percent co-founder can tell an investor that the CEO doesn't think this person matters much. Team strength is one of the main reasons early investors say yes, so a split that undervalues the team can undercut your own pitch.

4. Equity is the fuel for the bad months. Most startups fail, and the team that stays motivated through the low stretch tends to have better odds. A co-founder who holds a small slice while carrying half the load in year three may start to resent the deal, however happily they signed it. One way to frame the CEO's job: pick the split that keeps the whole team committed across all four vesting years, not the split a co-founder will accept on day one.

Reasons that do and don't justify an unequal co-founder equity split

Many arguments for a big gap fall apart once you picture the company three years out. Here's how we tend to sort them. Your facts may differ.

Reasons that usually fail:

It was my idea. Execution usually decides the outcome more than the idea.
I started six months earlier, raised the first check or shipped the first version. In a software startup, nearly all of the work is still ahead after an MVP or a small first round.
I'm older and more experienced. If the person is truly a co-founder, the company likely can't succeed without them. That argues for generosity, not a discount.
My co-founder needs a salary and I don't. Salary covers what someone needs to live; equity is what motivates. Many teams pay each founder what they need and set equity separately, rather than trading one for the other.
My co-founder agreed to it. Agreement today isn't motivation later. The CEO has to think about year three even if the co-founder isn't.

Reasons that can hold up:

One founder is full time and the other isn't. In our view a part-time founder is really an advisor or an early hire until they commit.
One founder contributes substantial cash or IP the company genuinely needs.
One person is plainly an early employee rather than a co-founder.

Watch the size of the founding group too. A team with five, six or seven co-founders usually has a hard conversation it hasn't had yet. We'd reserve the title for the smallest group needed to build the MVP and start learning from customers.

How to split equity between co-founders: a seven-step process

Decide who is a co-founder. If you're still looking, a good starting point is how to find a co-founder and a trial project first, as the founder dating playbook describes. List only the people who are full time (or about to be) and essential to building and selling the first product. Everyone else is usually an early hire and belongs in the option pool.
Start from equal. Put the same number on every founder. For any gap, try writing the reason in one sentence. If you can't, staying equal is often the simpler choice.
Settle the tie-break before you need it. A pure 50/50 deadlock has ended companies. One fix we like: the CEO holds one extra share, with a written agreement that it exists only to break stockholder deadlocks. A second, separate safeguard is to keep the CEO as the sole director until a significant priced round.
Put every founder on vesting. A typical schedule is four years with a one-year cliff, CEO included. See our guide to founder vesting and the 83(b) election for the mechanics and the tax filing.
Agree on what happens if someone leaves. It's far easier while everyone is friendly. The next section sets out the terms we'd start from.
Test any trade with the equity equation. Paul Graham's July 2007 essay "The Equity Equation" gives a clean check: giving up a fraction n of the company is worth it if the trade multiplies the company's average outcome by more than 1/(1 - n). Bringing on a third co-founder at one third requires them to raise the average outcome by at least 1.5x. For a genuinely essential co-founder that bar is low, which is the math behind our start-equal default.
Write it down and issue the stock. People remember early conversations differently. Record the split in a founder agreement, then have each founder buy their shares through a restricted stock purchase agreement.

Protect the split: vesting and departure terms

Vesting is what makes a generous split safe. The cliff works like cheap insurance: a founding-team mistake caught and fixed inside the first twelve months costs the company almost nothing. The standard mechanics, as Cooley GO's founder stock guide lays them out, are four-year vesting with a one-year cliff and monthly or quarterly vesting after that, with the company able to repurchase unvested shares at the lower of the original price or fair market value. We've made the same case for vesting and settling the split early in our earlier piece on splitting startup equity.

Vesting handles the default case. For a breakup before product-market fit, YC's Michael Seibel offers guidelines that we think are a sensible starting point for a negotiated exit (they are norms, not legal terms):

A founder who leaves or is fired before the one-year cliff typically ends up with only a token amount.
After the cliff but still before product-market fit, the departing founder keeps no more than about 5 percent of the company, which can mean handing back some vested shares.
A small severance of one to three months is reasonable when a founder is fired, and uncommon when a founder chooses to leave.
Every departing founder resigns from the board, signs a release, and often gives the remaining founders a proxy to vote their shares.

Whatever the split, we'd keep the CEO's ability to remove a founder who isn't performing, and put that in writing before anyone needs it.

Why plan for this? Because breakups are common. Carta's June 2026 analysis of two-founder teams found that for startups founded from 2016 to 2021, somewhere between 25 and 35 percent of two-founder teams had parted ways within five years, and more than 40 percent of teams founded from 2016 to 2018 had split up within eight years.

Worked example: a three-founder cap table from formation to seed

An illustrative company, recomputed in Python. Three founders incorporate and buy 9,000,000 shares of common stock at $0.0001 per share. The CEO, who started the project three months earlier, gets 34 percent; the CTO and the head of product get 33 percent each. Every founder vests over four years with a one-year cliff.

Holder	Shares held after seed	Ownership at formation	Ownership after seed
CEO	3,060,000	34.0%	21.82%
CTO	2,970,000	33.0%	21.18%
Head of product	2,970,000	33.0%	21.18%
SAFE holder, seed investors and pool	5,025,974	0%	35.83%

The company then raises $500,000 on a post-money SAFE with a $6M valuation cap, which converts into 818,182 shares (8.33 percent before the priced round). A year later it raises a $3M seed at a $12M pre-money valuation, with the option pool topped up to 10 percent of the post-money inside the pre-money. The seed investors buy 2,805,195 shares at about $1.07 each (20 percent), the pool holds 1,402,597 shares, and the SAFE holder ends at 5.83 percent because, under the post-money SAFE, the new pool and the new money both dilute it. There are 14,025,974 shares in total, and the three founders together hold 64.17 percent. Our cap table management guide shows how to keep this record current as rounds close.

The same company with a 70/15/15 split. If the CEO had taken 70 percent, the CTO and head of product would each hold 9.63 percent after the seed. That's the risk with a lopsided split: two people doing co-founder work for less than a tenth of the company each, before a Series A dilutes them further.

The breakup. Now suppose the head of product leaves at month 18, before product-market fit and before the SAFE converts. Under the vesting schedule she has earned 18/48 of her 2,970,000 shares, or 1,113,750 shares. The company repurchases the 1,856,250 unvested shares at the $0.0001 she paid, a total of $185.63. Her vested stake is 12.4 percent of the 9,000,000 shares outstanding. If the founders apply the pre-product-market-fit norm of about 5 percent (450,000 shares), they would ask her to return another 663,750 vested shares in exchange for the release.

Without vesting, she would keep a third of the company. That's a lot of equity riding with someone who no longer shows up, the kind of dead weight we flag when we read a cap table before the deck.

"But a formula is fairer than a gut call"

Not every serious operator agrees with a start-equal default, and the case against it is worth hearing.

Slicing Pie, a model created by Mike Moyer, takes the opposite approach. Each person's share equals their share of the at-risk contributions (unpaid time, cash, equipment, relationships) and keeps adjusting until the company breaks even or raises enough to pay people, at which point the split freezes. Supporters argue it's fairer to uneven contributions, and it can suit bootstrapped teams where people contribute unevenly and part time.

The data also shows equal splits are rising but still aren't the majority. Carta's February 2025 analysis, which used a different sample from the June 2026 study, found that 45.9 percent of two-founder teams formed in 2024 split equally, up from 31.5 percent in 2015, while equal splits among three-founder teams rose from 12.1 to 26.9 percent. Its median three-founder split moved from 50 percent for the lead founder and 13 percent for the third in 2019 to 44 and 22 percent in 2024. Carta's earlier study (October 2021, 7,764 companies founded from 2019) found that most teams have a lead founder with an outsize stake. Sector matters too: Carta's 2026 data shows a 58 percent lead-founder share in a typical two-founder biotech team, where a scientific founder often brings years of prior work.

But for a venture-backed startup, we'd be cautious about dynamic formulas. Goals shift every time you pivot, founders may work harder when they know what they own, and vesting with a cliff already handles much of what these formulas try to solve. Founder equity is a poor place to innovate, in our view.

Where we land

Start equal. Allow a small CEO premium if it comes with a written reason. A large one should have a reason that would survive an investor's question, and a biotech founder bringing years of prior science is a different case from a CEO who registered the domain.

It's our default, not a law. Your team's facts may point elsewhere.

On deadlocks, the one-extra-share tie-break and a CEO-only board are compatible but different tools. One settles stockholder votes; the other keeps board decisions with the CEO. Many early teams use both.

Co-founder equity split checklist

One option is to copy this into your founder agreement notes and fill it in together:

[ ] Named co-founders: full time, essential to the MVP (list each)
[ ] Proposed split, with a one-sentence reason for any gap from equal
[ ] Tie-break: one extra share for the CEO, or another written mechanism
[ ] Vesting: 4 years, 1-year cliff, monthly after, for every founder including the CEO
[ ] Vesting credit for pre-incorporation work (if any), stated in months
[ ] Departure terms: before the cliff, after the cliff, fired vs. left, severance
[ ] Board: who sits on it until the first priced round
[ ] Salary: each founder's minimum need, handled separately from equity
[ ] IP: every founder assigns all startup-related IP to the company
[ ] 83(b) elections filed within 30 days of each stock purchase

Co-founder equity mistakes we'd avoid

Negotiating instead of designing. A split reached by haggling optimizes for today. Design it for year three.
Skipping vesting because the founders trust each other. Illness, family changes and burnout happen to good people.
Too many co-founders. Titles are cheap to hand out and expensive to take back.
Adding the co-founder after the idea and the raise. Finding the co-founder first helps the idea and the company feel jointly owned.
Leaving it unwritten. Memory is unreliable, and an unsigned split can turn into a diligence problem.

If you're a first-time founder still shaping your MVP and your founding team, 1752vc's Ignite academy is built for that stage: a 12-week program, run live and remote at your own pace, with rolling admissions, so you can join while you're still settling who is on the team and building the first version. Learn more at Ignite.

The bottom line

The split you sign in week one has to hold up in year three, when the work is hard and nobody remembers who had the idea. Start equal, vest everyone, agree the exit terms while you're still friends, and write it all down.

The idea gets you a conversation.

The next four years earn the equity.

Key takeaways

In our view, an equal or near-equal split among essential, full-time co-founders often makes sense, because nearly all the work and value creation is ahead of you.
Four-year vesting with a one-year cliff for every founder, including the CEO, is a common way to protect a generous split.
Carta's June 2026 data puts equal two-founder splits at 44.6 percent of 2025 formations, up from 34.5 percent in 2016, with a 51 to 49 median.
Agreeing departure terms early helps; under YC's Michael Seibel's norm, a founder who leaves before product-market fit usually keeps no more than about 5 percent.
Paul Graham's 1/(1 - n) test is a useful check on whether giving up equity makes the company more valuable.

Frequently asked questions

Should co-founders split equity 50/50?

Often yes, if both founders are full time and essential, and Carta found 44.6 percent of two-founder teams formed in 2025 split exactly equally. The main risk is a voting deadlock. A simple fix is to give the CEO one extra share, agreed in writing, purely as a tie-break, and to keep the CEO as sole director until the first priced round.

What is the average equity split for two co-founders?

Carta's June 2026 analysis of companies formed on its platform puts the median two-founder split in 2025 at 51 to 49, down from 57 to 43 in 2021. About 44.6 percent of two-founder teams split exactly equally. Biotech is the notable exception, with the lead founder typically holding 58 percent, often because a scientific founder brings years of prior work.

How much equity should a co-founder who joins later get?

In our view, less than an equal share mainly when the company has made real progress, such as paying customers, that reduced the risk the newcomer takes on. An MVP or a small first round usually leaves nearly all the work ahead, so a late co-founder often merits a meaningful stake. The late joiner typically starts a fresh four-year vesting schedule.

How much equity should a departing co-founder keep?

It depends on the vesting schedule and the founders' agreement. Under standard vesting, a founder who leaves before the one-year cliff keeps nothing, and later leavers keep only vested shares. For departures before product-market fit, a common norm is that the leaver keeps no more than about 5 percent, which can mean returning some vested stock in exchange for a release.

Is it bad to give the CEO more equity than the other co-founders?

A small premium is common and usually harmless; a large one sends a signal. Carta's data shows most teams still have a lead founder with a somewhat bigger stake. Investors can read a very unequal split as a sign the CEO undervalues the team, so it often helps to keep any gap small and tied to a lasting, written reason.

Sources

Disclaimer: This guide is for general education only and is not legal, tax or investment advice. Laws, market data and program terms change, so it may not reflect the latest developments or fit your situation. Treat it as a starting point, not a source of truth, and talk to a qualified lawyer, accountant or financial adviser before you make decisions.