My cofounder quit after three months. Do they keep their shares?

Vesting means earning your shares over time instead of owning all of them on day one. Shares you have earned are vested. Shares you have not earned yet are unvested.

A cliff is the first stretch of the schedule, when nothing vests at all. If you leave before the cliff ends, you leave with no vested shares from that agreement. At the cliff, a block vests at once, then the rest usually vests month by month.

Carta's guide calls a four-year vesting period with a one-year cliff the industry standard for founders. It says the same for employees (Carta, Vesting Explained: Schedules, Cliffs, Acceleration, and Types, 29 July 2026). Carta is a platform many startups use to manage ownership records. Your own agreement can say something different.

It depends on which of these is true for you:

• You signed vesting with a cliff: after three months, your cofounder is still before the cliff. Usually none of their shares have vested.
• You signed vesting with no cliff: they keep the part that vested month by month, a small slice after three months.
• You signed nothing about vesting: they may keep all the shares in their name. In our reading, that is the case founders regret most.

That depends on the agreement. In our plain-language summary, founder shares are often issued up front. The company then has a right to buy back the unvested part if the founder leaves, often at the low price the founder first paid. In other set-ups, unvested shares are simply cancelled or never issued. Read your own documents, because the wording decides it.

Here is an illustrative example with made-up round numbers. Say two founders each hold 1,000,000 shares on four-year vesting with a one-year cliff, which is 48 months.

• Leaves at 3 months: before the cliff, so 0 shares vested. The company can usually buy back all 1,000,000.
• Leaves at 12 months: the cliff has passed, so 12 of 48 months have vested: 250,000 shares kept.
• Leaves at 18 months: 18 of 48 months vested: 375,000 shares kept.

Without any vesting, the founder who left at 3 months could keep all 1,000,000. The founder who stays then does all the work for half the company.

Because investors look at who owns the company. A large share held by someone who no longer works on it can make a round harder. Carta's guide warns that without vesting, a departing cofounder could walk away with a significant piece of a company they are no longer helping to build (29 July 2026).

Investors often check founder agreements during due diligence, the checks they run before investing. What investors ask in due diligence covers what they look for. Founder terms can also come up in a term sheet, the short summary of an investment deal. See what term sheet phrases mean.

Then the honest answer is that you need a lawyer where you live. Options can include asking your cofounder to agree to sell back some shares, or agreeing a new split together. These depend on their agreement and your local law.

The strongest case against acting fast: a sudden legal letter can turn a friendly exit into a fight. The missing fact is how your cofounder sees it. A calm conversation first often costs less than a dispute.

Put vesting in writing before anyone leaves, ideally when you first split the company. Write down what happens if someone leaves early, while everyone is still friends. It feels awkward for an hour. It is far less awkward than the conversation you are having now.

Gather every signed document about founder shares. For each founder, write down the number of shares, whether they vest, the cliff length, and whether the company can buy back unvested shares. Take that one page to a startup lawyer before you talk to any investor.