Start a business with a co-founder: legal form and the agreement you sign first

When you start a business with a co-founder, it often begins like this. Two friends from college set up a renovation business as a partnership. They split everything half and half and put nothing on paper. In year three one wants to expand and the other does not, and the first signs a lease for a second van anyway.

That is when the law takes over. In the UK, every partner in a firm is liable jointly with the other partners for all debts and obligations of the firm incurred while they are a partner (source: The National Archives, October 2026). In the Netherlands a partner in a general partnership is liable for the whole amount of its debts, and creditors can claim each partner's personal assets once the business assets fall short (source: Netherlands Chamber of Commerce KVK, April 2024). The van lease is now a problem for both of them.

The legal form is only half the work. A general comparison is in choose a legal structure; other starting points are in your starting situation.

Why start a business with a co-founder, and where it chafes

Good co-founders complement each other: one masters the craft, the other sells. You share the investment, the work and the decisions. You share the risk less than it seems: in a general partnership a creditor can hold each partner to the full debt.

The relationship itself also shifts. Noam Wasserman analysed 212 American start-ups founded in the late 1990s and early 2000s (source: Harvard Business Review, February 2008). By the time the ventures were three years old, 50% of founders were no longer CEO, in year four only 40% were, and fewer than 25% led their company's initial public offering (source: Harvard Business Review, February 2008). Those were venture-backed start-ups, but the lesson holds: the roles you agree at the start are rarely the roles of five years later.

How founders split ownership is often decided too quickly. In data on 1,476 founders in 511 ventures, Thomas Hellmann and Noam Wasserman found that roughly one third of founder teams divide their equity equally, and that equal splitting is associated with lower valuations in the first financing round (source: National Bureau of Economic Research, August 2011). An equal split is not wrong, but it should follow from equal contributions, not from politeness.

Partnership or company: who is liable for what?

In a general partnership, the partners and the business are largely one pocket for creditors. A limited company or LLC is a separate legal person, which shields your private assets in most cases. How that works in a few markets:

A company does not remove every risk: lenders and landlords often ask founders of a young company for a personal guarantee. Rules change, so check the official source in your country.

What to put in a founders' agreement

In a partnership this is the partnership agreement; in a company, the shareholders' agreement alongside the articles of association (the company's own rulebook). Answer these questions together before you sign anything else:

• Roles and time: who does what, and how many days a week.
• Contributions: who brings money, equipment, clients or code, at what value, and whether it is transferred or only lent.
• Equity, vesting and cliff: who owns what and why. With vesting, founders earn their shares over several years; the cliff means a founder who leaves in the first year keeps nothing.
• Pay and profit: salaries or drawings per founder, and how the remaining profit is shared.
• Decisions and deadlock: what each may decide alone, what needs both signatures, and who breaks a tie when shares are equal, such as a mediator or an independent chair.
• Intellectual property: everything founders create for the business belongs to the business, including code written before it was set up.
• Non-compete: what a departing founder may not do, for how long and where.
• Illness, disability and death: how long pay continues, what heirs receive, and whether insurance on each founder funds a buy-out.
• Exit and buy-sell clauses: notice, good and bad leaver rules, the valuation formula, payment terms, and a shotgun clause: one founder names a price, the other must buy or sell at it.

Worked example: two software developers set up a company

Lena and Omar, both software developers, start a custom software studio. Client contracts carry liability if a project fails, so they choose a private limited company. Lena brings €20,000 and works five days a week; Omar brings €10,000 and their first client, and works four days. They do not turn this into a two-thirds, one-third split. Each puts €10,000 into share capital, for 500 shares at €20, and Lena lends her extra €10,000 to the company at 5% interest. Salaries follow time: €900 a month for each weekday worked. Shares vest monthly over four years with a one-year cliff. They expect a first-year profit of €130,000 before founder pay.

Fictitious Firmfocus example. Amounts per year, before corporate and personal income tax. Whether the remaining profit is paid out or kept in the company is a separate decision. The logic works in any currency.

With a plain equal split of the €130,000, each would receive €65,000: Omar the same for four days as Lena for five, and Lena's extra money would earn nothing. Paying for time and money first, and sharing only what remains, keeps the equal shareholding fair. See also pay yourself.

What happens when a co-founder leaves after three years?

After three years Omar joins a large software firm. He leaves on good terms, so the agreement treats him as a good leaver. Of his vesting period, 36 of 48 months have passed. Lena buys his unvested shares at their €20 issue price and his vested shares at fair value, using a formula they agreed on day one: net assets on the balance sheet plus goodwill (the value of the business above its assets), set at the average remaining profit of the last three years.

Fictitious Firmfocus example. The formula is their own agreement; other valuation methods exist. Lena's loan to the company is repaid on its own terms.

Without vesting, Omar would keep half the company while Lena does all the work, or ask €48,000 for his 500 shares. Had he left to start a competing studio in breach of the non-compete, the bad leaver clause would have priced all his shares at €20. Because everything was fixed in advance, the departure is about carrying out the rules, not making them. On death or long-term disability the same formula applies, funded by insurance.

Working together small, or building a company together

Pitfalls when you start with a co-founder

• Half and half by habit: fair only with equal contributions and effort.
• No agreement on drawings: an imbalance grows unnoticed.
• No exit clause: you then negotiate the price at the moment you get along worst.
• Intellectual property left with a founder: it blocks a later sale or investment.
• An agreement in the drawer: review it when you hire, when a partner joins or when roles shift.

Planning the money side together? Start with the business plan. Other starting points are in your starting situation, and the full theme in Start a business.