Can I structure a deal so I get an option to buy the remaining shares later?

Yes — buying an initial stake with a contractual option to acquire the remaining shares later is a recognized structure, often used where a seller wants to stay involved for a transition period, or where a buyer wants to prove out the relationship or the business's performance before fully committing. The option is typically documented in a shareholders' agreement alongside the initial share purchase agreement.

The details matter more than the concept. The agreement needs to set out when the option can be exercised, how the price for the remaining shares will be determined — a fixed formula agreed now, or a valuation process at the time the option is exercised — and what happens if one side wants to trigger it and the other resists. It's also worth addressing the reverse: whether the remaining seller has a corresponding right to require you to buy them out, sometimes called a put, rather than the option only running one way.

Because these terms govern a relationship that may run for a meaningful period before the option is exercised, and because valuation disputes are a common source of friction later, a business lawyer should draft the option mechanics as carefully as the initial purchase itself.