Choosing a co-founder is one of the biggest decisions in an early business, and it is usually made faster and more casually than choosing a flatmate. This piece is about doing it on purpose.
Do you even need one?
A co-founder is not a requirement. Plenty of businesses, especially service businesses, shops and one-person products, are started and run by one person. A partner is worth it when they bring something you genuinely lack and can't easily hire: a skill (one builds, one sells), a network, capital, or simply the stamina of two people carrying a hard thing together.
A partner is not worth it just because starting alone feels lonely, or because a friend is enthusiastic. Enthusiasm is cheap in month one. What matters is who is still showing up in month twenty.
A co-founder is not a hire you can let go. Choose them the way you would choose someone to share a mortgage with.
The questions to ask before you shake hands
Most partnerships that break do so over things that could have been discussed at the start. Before you commit, sit down and answer these out loud, together:
- Time: Is this full-time for both of us? If not, when, and what happens if one person can't make that jump?
- Money: Who is putting in cash? How long can each of us go without a salary? (Two people with very different savings have very different patience.)
- Roles: Who decides what? Who has the final word on product, on money, on hiring?
- Ambition: Is this a lifestyle business that pays us well, or a company we want to grow big and maybe sell? Both are fine. Wanting different ones is a slow-motion breakup.
- Exit: If one of us wants out in two years, what happens to their share?
If a question feels too awkward to ask now, it will be far more awkward to argue about later, when there's money on the table.
Try a small project first. The best test of a working partnership is working together. A weekend build, a pilot with five customers, a month of real effort. You learn more about someone from one missed deadline than from ten enthusiastic dinners.
Splitting the equity
Equity is who owns what share of the company. There's no single correct formula, but there are two traps.
Trap one: the reflexive 50/50. An equal split can be exactly right when two people really are contributing equally. The trouble is when it's chosen to avoid a conversation. Researchers Thomas Hellmann and Noam Wasserman studied 1,476 founders in 511 young companies and found that roughly a third of teams split equally. Equal splits were linked to lower valuations when the companies first raised money, and the effect was strongest in teams that decided the split quickly. The authors argue this mostly reflects teams glossing over real differences between founders, rather than equality being bad in itself.
Trap two: deciding by who had the idea. Ideas are cheap; execution is the business. Weigh what each person will contribute over the next few years (time, skills, money, risk taken) more heavily than who said "what if" first.
| Ask about each founder | Why it matters |
|---|---|
| Full-time or part-time? | Time is the main thing being contributed early on |
| Cash put in? | Money at risk deserves recognition (or treat it as a loan) |
| Salary given up? | A founder working unpaid is investing too |
| Hard-to-replace skill? | The person who can build or sell the product carries the most weight early |
Vesting: the clause that saves friendships
The single most useful protection is vesting: founders earn their shares over time instead of receiving them all on day one. If a founder leaves early, the company can buy back the unearned part. Typical schedules run three to five years, often with a "cliff" of six or twelve months, meaning nothing is earned until the cliff date, and then shares are earned steadily after that.
Go back to the kitchen-table story. With vesting, the friend who left after eighteen months would keep only the part he had earned, and the rest would go back to the company, available for whoever actually builds it. Without vesting, the person still working is stuck carrying a passenger.
Vesting isn't about distrust. It protects whichever of you ends up staying, and neither of you knows yet who that will be.
In the US there's a tax detail founders often miss: if you receive shares that vest over time, you may need to file an 83(b) election with the IRS, and the legal deadline is 30 days after the shares are transferred. Missing it can create a large tax bill later. Rules elsewhere differ, so this is exactly the moment to pay for an hour of a lawyer or accountant's time.
Put it in writing
Everything above belongs in a founders' agreement (or a shareholders' agreement, depending on your country and company type): who owns what, the vesting schedule, roles, how decisions are made, and what happens if someone leaves, gets ill, or wants to sell. As The Legal Bare Minimum in this library puts it, write this down on day one, while everyone is still friends. It is the cheapest insurance a young company can buy.
This is general information, not legal or tax advice. Company structures, equity rules and tax treatment vary by country. Have a qualified local professional review your agreement.
The takeaway
A co-founder should bring something essential you can't easily hire, and should share your answers on time, money, roles, ambition and exit. Test the partnership on a small project before committing. Split equity by what each person will contribute over the next few years, not by who had the idea or by reflex. Make founders' shares vest over time, and put the whole deal in writing while everyone is still on good terms.
Try this: if you have, or are considering, a co-founder, each of you write down your answers to the five questions above (time, money, roles, ambition, exit) separately. Then swap papers. The places where your answers differ are your first agenda.
Sources & Further Reading
Sources
- Hellmann, T. & Wasserman, N. (2011), The First Deal: The Division of Founder Equity in New Ventures, NBER Working Paper 16922 (1,476 founders in 511 ventures; about a third split equally; equal splits linked to lower pre-money valuations, especially when decided quickly).
- Vesting periods and cliffs: typical US practice as summarized in standard references on equity vesting (3–5 years; 6- or 12-month cliffs).
- 83(b) election deadline: US Treasury Regulation 26 CFR § 1.83-2(b) ("not later than 30 days after the date the property was transferred").
Go deeper
- 📘 The Founder's Dilemmas — Noam Wasserman (built on data from about 10,000 founders of 3,500 startups; the definitive book on co-founder decisions)
- 🌐 NBER — The First Deal (Hellmann & Wasserman)
- 🌐 Companion piece: The Legal Bare Minimum (in this library) — structures, contracts and the other early paperwork