A part-time cofounder equity split holds up when the number can move. Set a starting split, tie vesting to milestones or a written hours commitment, and add a trigger for when the part-time founder goes full-time. Decide now what happens if they never do. If the role is really advisory, make it an advisor role.
Why does unequal time cause so much resentment?
Because the gap grows every week nobody mentions it. One founder is at their desk by 8am and answering support tickets at 11pm. The other gives ten focused hours around a day job, another venture or caring for family. Both started together. Only one is building most of the company now.
Founders split equity on what is true at signing: who had the idea, who put in money, who holds which title. Time gets treated as fixed, but it is the thing most likely to change. Capbase's guide to splitting equity among co-founders asks the question directly: "Are they committed on a part time or full-time basis?"
Six months in, the full-time founder holds decisions, relationships and product knowledge the other was not there for. A flat 50/50 or 60/40 with no way to adjust is how equity resentment between cofounders starts.
Should you use milestone vesting or time vesting?
Either works if it is written in numbers. Pick the one that matches how the part-time founder contributes.
| Milestone vesting | Adjusted time vesting | |
|---|---|---|
| Equity vests when | A defined result is delivered | Time passes at a stated hours level |
| Suits | Uneven, project-shaped work | Steady but limited hours |
| Example | Working prototype, first paying customer | 15 hours a week, reviewed every quarter |
| Watch for | Arguments over whether a milestone was met | Hours drift and nobody tracks them |
TechCrunch's case for milestone-based vesting for startup founders argues that startup value "does not grow linearly" and suggests milestones such as a working prototype or customers. A part-time founder who hits milestones on a slower calendar is still treated fairly. One who stalls stops vesting.
Time vesting usually means the four years with a one-year cliff that Y Combinator describes. For a part-time founder, tie the rate or the cliff to a stated minimum. If one founder gives 15 hours a week and the other 55, the agreement should say so. "Committed" means different things to different people; "15 hours a week, reviewed every quarter" does not. Our vesting schedule explainer covers cliffs and acceleration.
What is a full-time conversion trigger?
A clause in the founders' agreement that says when the part-time founder is expected to go full-time, and what happens to their equity when they do. Leaving it unsaid is where most of these deals go wrong: one founder assumes conversion is certain, the other treats it as optional.
Write down three things:
- The trigger: a date, a funding close or a revenue level.
- What happens to vesting at conversion: unvested shares move onto the full-time schedule, a one-time top-up, or no change because the original split already assumed conversion.
- What happens if conversion does not happen: vesting pauses, the stake is renegotiated, or the role becomes an advisor role.
Decide this now, while it is still hypothetical. The cofounder agreement checklist shows where this clause sits next to the other terms.
What about an outside job or another venture?
Most part-time founders have something else taking their hours. That is fine when it is defined. Before you settle the split, get answers to these:
- How long will the outside commitment last?
- Does it conflict with the company through the same industry, shared customers or shared IP?
- Is there a hard cap on hours, or does "part-time" mean whatever time is left over?
An outside job with an end date and no conflict is a scheduling fact. An open-ended one, or one in a nearby market, is a governance question for the founders' agreement before it is an equity question. If you already see this differently, the cofounder alignment check shows where your answers differ.
When should a part-time contributor be an advisor instead?
When their involvement is limited: occasional strategic input, some introductions, a view on big decisions without running anything. Advisor equity sits far below a cofounder stake and comes without founder decision rights or a board seat.
Hours alone do not settle it. Ask whether the person carries real operating responsibility and makes calls that shape the company. Calling an advisor a part-time cofounder sets an equity number that will look wrong to everyone, including them, once the company is worth something. If you are already arguing about it, our cofounder conflict resolution guide helps you work through it.
Frequently asked questions
- Should a part-time cofounder still get a standard four-year vesting schedule?
- You can keep four years with a one-year cliff, but add conditions that fit the part-time arrangement: a minimum weekly hours level, a date by which they are expected to go full-time, or milestones tied to what they deliver. Write the conditions in numbers so both founders read them the same way.
- What is a full-time conversion trigger clause?
- A clause in the founders' agreement that sets what happens to equity when a part-time cofounder moves to full-time. Usually that is faster vesting, a one-time top-up, or a move onto the full-time founder's schedule. It is tied to a named date or event, such as a funding close, instead of a vague promise.
- Should a part-time cofounder with an outside job get the same equity as if they had none?
- Usually not, unless the outside commitment is bounded and disclosed: a fixed end date, capped hours and no conflict of interest. An open-ended job or a competing venture is a governance question first and an equity question second. Settle how it will be handled in the founders' agreement before you finalise the split.
- When should a part-time contributor be an advisor instead of a cofounder?
- When their involvement is limited and not central to running the company: reviewing decisions, opening doors, occasional strategic input. Advisor equity sits far below a cofounder stake and does not carry founder decision rights or a board seat. Ask whether they carry real operating responsibility. If they do not, make them an advisor.
- What happens if the part-time cofounder never converts to full-time?
- That is what the conversion trigger and vesting schedule are for. If the deadline passes, unvested shares stop vesting or return to the company as the agreement says. The relationship can then become an advisor role, a smaller ongoing stake or an exit, all decided in advance instead of in the moment.