Co-founder equity split: data, vesting and a worked example

Three friends, a kitchen table in Bologna, and one question nobody wants to ask first: who gets how much? It’s tempting to settle it in ten awkward minutes and move on. Those ten minutes can follow you for years.

Here’s what you need for a fairer co-founder equity split. We cover what the latest data says about equal and unequal splits, which factors should move the numbers, and how vesting and the cliff protect everyone. A worked example follows three founders through an option pool and a seed round. Then comes the Italian part, because in an SRL vesting works differently.

Equal or unequal? What the data says

Among pairs, equal splits are gaining ground. Carta’s February 2026 analysis covers 40,228 US startups. In 2025, 44% of two-founder teams split their equity (ownership of the company) equally, and the median split was 51/49. In 2015, only 31.5% went 50/50.

Why the change? Frances Mosley, a lawyer at DLA Piper quoted by Carta, talks about a ‘professionalization of the founder role’. More co-founders now work on the startup full-time from the start, and everyone is expected to earn their stake through work.

Three founders are another story. Only 27% of three-founder teams split equally in 2025, and the median split was 45/33/20. Those are medians, which is why they don’t add up to 100. They’re also American figures, so use them as reference points, not rules.

What should decide a co-founder equity split?

Start from what each person will put in over the next four years, not from who was in the room first. Five factors do most of the work:

• Time. Full-time from day one is worth more than evenings and weekends. If someone stays part-time for a year, the split can show it, or their vesting can start the day they go full-time.
• Role. Who would be hardest to replace? A CTO who builds the whole product carries more weight than an advisor with a nice title.
• Cash. Putting in €20,000 matters. But cash can also go in as a loan to the company, so it doesn’t have to buy a permanent slice.
• Risk. Leaving a permanent contract, or personally guaranteeing a bank loan, is a real cost.
• Opportunity cost. A senior engineer who turns down a well-paid job gives up more than a student with no offer on the table.

And the idea? It’s worth less than people think. An idea starts the clock; four years of building make it worth something. If one founder had the idea but the others will do most of the work, a big premium for the idea alone is hard to defend.

Back to Bologna. Say Giulia will be CEO, full-time, and puts in €20,000. Marco, the CTO, leaves a salaried job to build the product. Sara runs product and design but stays part-time for the first year. They settle on 45/35/20, close to Carta’s three-founder median. If you haven’t found your partners yet, start with how to find a co-founder.

Vesting and the cliff, in plain words

Vesting means you earn your shares over time. The schedule Carta describes as the industry standard for founders is four years with a one-year cliff. The cliff is a waiting period: leave before month 12 and you keep nothing. At month 12 a quarter of your stake vests in one go, then 1/48 of it every month until month 48.

Carta also notes that investors expect to see this structure. In practice it protects the founders from each other more than from anyone else. Here’s what it means for Sara’s 20%:

Months since the start	Share of each founder’s stake that has vested	Sara’s vested slice of the company
0 to 11	0%	0%
12 (the cliff)	25%	5%
24	50%	10%
30	62.5%	12.5%
36	75%	15%
48	100%	20%

If Sara leaves at month 9, nothing has vested and her whole 20% comes back. If she leaves at month 30, she keeps 12.5% of the company (20% × 30/48) and the other 7.5% goes back to the company or to the remaining founders, depending on how the agreement is written.

A worked example: three founders, an option pool and a seed round

Two years in, the team prepares a seed round, the first sizeable round from professional investors (here’s how the startup funding stages follow each other). The lead investor asks for a 10% option pool, shares set aside for future employees, to be created before the money arrives. Then the fund invests €500,000 at a €2 million pre-money valuation, the value of the company before the new money comes in.

Holder	At founding	After the 10% option pool	After the seed round (€500,000 at €2M pre-money)
Giulia (CEO)	45%	40.5%	32.4%
Marco (CTO)	35%	31.5%	25.2%
Sara (product)	20%	18%	14.4%
Option pool	0%	10%	8%
Seed investor	0%	0%	20%
Total	100%	100%	100%

Here’s the arithmetic, one step at a time. First the pool. Creating a 10% pool shrinks everyone by the same factor: 45% × 0.90 = 40.5% for Giulia, 31.5% for Marco, 18% for Sara. Then the round. It sells €500,000 ÷ €2.5 million (pre-money plus new money) = 20% of the company, so everyone else keeps 80% of what they had: 40.5% × 0.80 = 32.4% for Giulia, 25.2% for Marco, 14.4% for Sara and 8% for the pool.

One clause can change all of this. Suppose the investor wants the pool to be 10% after the round but created before it. The founders then absorb the full 30 points (20% sold plus a 10% pool): Giulia ends at 31.5%, Marco at 24.5%, Sara at 14%. Our guide to the employee option pool covers that negotiation, and fully diluted ownership explains how pools and convertibles are counted.

Real cap tables tend to be more diluted than this tidy one. In Carta’s 2026 report the median founding team keeps about 56% after the seed round; our three keep 72%. Pre-seed money, advisors and bigger pools all take their share. For seed benchmarks, see how much equity to give away at seed, and to keep every change in one file, read our guide to the cap table.

How vesting works in an Italian SRL

An SRL has quote (quotas), not shares, and there’s no ready-made restricted stock as in a US company. So vesting is built with contracts. Typically it’s a call option written into the patto parasociale (the shareholders’ agreement) and, where possible, into the statuto: if a founder leaves early, the other partners, and sometimes the investors, can buy back the part of the stake that hasn’t vested yet.

The price depends on why the founder leaves, and that’s what good leaver and bad leaver clauses decide. In the open-source pre-seed and seed contract framework published on EconomyUp in January 2024, for example, investors and the other partners can buy at nominal value the unvested part of a good leaver’s stake, and the entire stake of a bad leaver. Drafting varies a lot from deal to deal. This is where a good lawyer earns the fee.

One more Italian tool is worth knowing. A startup innovativa set up as an SRL can create categories of quotas with different rights, for instance quotas without voting rights, and since 2017 the same freedom extends to any SRL that qualifies as an SME. That’s what lets you give investors, or a future team plan, a separate class of quotas.

The mistakes that cost founders the most

• A 50/50 with no way out of a deadlock. When two equal partners disagree, nobody wins the vote. Under the Italian civil code (art. 2484), an assembly that can’t function or stays inactive is a cause of dissolution. Agree a tie-break in advance. The Milan notaries (massima 181, 2019) accept the so-called Russian roulette clause, where one partner names a price and the other must buy or sell at it, provided the partner forced out gets a fair value.
• Dead equity. A co-founder walks away in year one and keeps 30% because nothing vested. To a new investor that’s a big slice of ownership with no work attached.
• No vesting because you trust each other. Trust is exactly why you write it down now, while nobody knows who’ll burn out, fall ill or get an offer they can’t refuse.
• Splitting before you’ve worked together. Why not test it? A short trial project gives you something better to split on than first impressions.

Your checklist before you sign

1. For each founder, write down time, role, cash and risk over the next four years.
2. Put a first split on paper and compare it with Carta’s medians (51/49 for two founders, 45/33/20 for three).
3. Agree four-year vesting with a one-year cliff, and decide who can buy back unvested quotas.
4. Define good leaver and bad leaver, with a price for each.
5. Pick a tie-break mechanism, especially at 50/50.
6. Model one seed round with a 10% pool before you sign anything.
7. Ask a lawyer or notary to turn it into a patto parasociale and, where possible, clauses in the statuto.

On the beginner’s map from zero to first round, the next stop is the team you’ll build around you. Still studying? See how to start a startup at university.

This article is general information, not legal or tax advice. Rules and market practice change: have a lawyer, notary or accountant check your agreement before you sign.