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Founder equity split: how to divide shares, vesting, cliffs and examples

Most cofounder teams split equity by weighing who does what and who takes the most risk, then put every founder's shares on a vesting schedule. A common setup is a near-equal or modestly weighted split, with shares earned over four years and a one-year cliff. There is no legal formula, and no calculator can replace the conversation, but a few principles keep splits from becoming disputes later.

This guide covers how to choose a split, how vesting and cliffs work, what the 83(b) election does, and what happens when a cofounder leaves. It is general information as of October 2026, not legal or tax advice.

Equal or weighted: how to choose a split

An equal split is the simplest and avoids an early argument about who is worth more. A weighted split makes sense when contributions are clearly different. The question to ask is not who had the idea, but who will carry the company over the next several years.

Factors founders typically weigh:

• Time commitment. A full-time founder and a part-time one are not equals.
• Role and scarcity. The person running the company and the person building the product often carry more than a founder with an advisory role.
• Money and assets put in. Cash, code or IP contributed before incorporation can justify a different weighting, but treat it as a separate negotiation.
• Risk taken. Someone who quit a job on day one carries more risk than someone who joins after a funding round.
• Future dilution. Investors, an option pool and later hires all shrink every founder's percentage, so small gaps between founders matter less than the total size of the pie.

A very lopsided split between people doing the same work tends to breed resentment. A split that ignores real differences does the same. Whatever you choose, write it down and have every founder agree to it before incorporation, not after the first investor asks.

Why a calculator only goes so far

Searches for a founder equity split calculator usually lead to a scoring tool: you rate each founder on factors like commitment and experience, and the tool turns the scores into percentages. These are useful as a structured conversation. They are not a standard, and the output is only as good as the inputs you agree on.

What vesting means for founders

Vesting means a founder earns their shares over time instead of owning them outright on day one. If someone leaves early, the company can buy back the shares that have not vested, so a departed cofounder does not walk away with a large stake in a company they no longer work on. Investors normally expect it, and it protects the founders who stay.

The structure most often used in US startups is:

• Four-year schedule. The shares vest gradually, usually monthly, over 48 months.
• One-year cliff. Nothing vests until the first anniversary. On that date a quarter of the shares vest at once, then the rest vest month by month.

The term "cliff vesting" describes this all-or-nothing start; general references on vesting note that startup equity often carries a six- or twelve-month cliff. Four years with a one-year cliff is a convention, not a rule, so shorter cliffs, longer schedules and credit for time already worked are all negotiable.

Credit for work already done

If founders have been building for months before incorporating, they can start with part of the schedule already vested. A common compromise is to credit some of the prior time while keeping most of the shares subject to vesting. Investors who join later may ask for a reset, so agree this early.

Acceleration: single trigger vs double trigger

Acceleration makes unvested shares vest early when a defined event happens, most often a sale of the company.

• Single trigger: one event, such as an acquisition, vests the remaining shares.
• Double trigger: two events are needed. The company is acquired, and the founder is then terminated without cause, typically within a set window after the deal. Reference sources describe a window of roughly 9 to 18 months and call double trigger the market standard in venture-backed companies.

Buyers generally prefer double trigger because single trigger can remove the incentive for founders to stay after closing. Whatever you agree, check the exact wording on what counts as "cause" and "good reason".

The 83(b) election

When founders buy shares that are subject to vesting, US tax rules can treat each vesting date as a taxable event on the difference between the shares' value then and what the founder paid. An 83(b) election lets the founder instead pay tax on the difference at the moment of the purchase, which for a brand-new company is often small.

The deadline is strict. Under section 83 of the Internal Revenue Code, the election must be made no later than 30 days after the shares are transferred, and there is no extension. The IRS offers Form 15620 (Section 83(b) Election) for this purpose. Our step-by-step guide to the 83(b) election and Form 15620 covers filing, proof of mailing and the risk if the stock is later forfeited.

Founders outside the US should check how their own country taxes restricted shares; this rule is specific to US federal tax.

What happens when a cofounder leaves

With vesting in place, the outcome follows the schedule and the agreement the founders signed:

1. Shares already vested stay with the departing founder.
2. Unvested shares are usually repurchased by the company, commonly at the price the founder originally paid, which is often very low.
3. The returned shares go back into the company, which benefits the remaining founders and any future hires.

Without vesting, a founder who leaves after a few weeks can keep a full share of the company. That is the single most common reason investors insist on it. If you are weighing how investors will view your cap table, see our guide to accelerator deal terms and our founders coverage.

Three illustrative examples

These are hypothetical cases, not real companies, and the numbers are chosen for clarity.

Example 1: two founders, equal split

Two founders each take 50 percent, vesting over four years with a one-year cliff. One leaves after eight months. Because the cliff has not been reached, none of their shares have vested, and the company repurchases all of them. The remaining founder is left with the whole founder pool.

Example 2: weighted split with a full-time lead

One founder works full time and runs the company; the other keeps a day job for the first year and joins full time later. They agree on 60/40, with the second founder's vesting starting on the date they go full time. The unequal split reflects the unequal risk, and the vesting start date keeps the part-time period from earning shares for free.

Example 3: three founders, one leaves after the cliff

Three founders each hold 30 percent with 10 percent reserved for early hires. After 18 months one founder leaves. Of that founder's four-year schedule, 18 of 48 months have vested, so 37.5 percent of their shares are theirs to keep and the remaining 62.5 percent return to the company. If those shares are repurchased and returned to the pool, the two remaining founders and future hires benefit.

A short checklist before you sign

• Agree the split in writing and have a lawyer review the stock purchase agreements.
• Apply the same vesting terms to every founder, unless there is a documented reason.
• Decide the vesting start date, cliff length and acceleration terms up front.
• File any 83(b) election within the 30-day window and keep proof of mailing.
• Revisit the split only through a deliberate, documented process. Later fundraising is covered in our funding section, and tax treatment of eventual gains is covered in our QSBS explainer.

Frequently asked questions

What is a typical founder equity split?

There is no single standard. Many teams choose an equal or near-equal split among founders who commit full time, and use a weighted split when roles, risk or timing differ clearly. Vesting matters more than the exact percentages.

Should cofounders split equity equally?

Equal splits work well when founders contribute similarly and join at the same time. If one founder carries clearly more responsibility or risk, a modest weighting is more honest than pretending the contributions match.

What is the standard vesting schedule for founders?

The most commonly used schedule is four years with monthly vesting and a one-year cliff. It is a convention, so the cliff length, schedule and credit for earlier work can all be negotiated.

Do I need an 83(b) election as a founder?

If your shares are subject to vesting and you are a US taxpayer, an 83(b) election is usually worth discussing with a tax adviser. It must be made within 30 days of the share transfer, and the deadline cannot be extended.

What happens to a cofounder's equity if they quit?

Vested shares stay with them, while unvested shares are generally repurchased by the company under the terms of the founder's agreement. Before the cliff date, that usually means no shares are kept.