Technical co-founder or fractional CTO, and how to tell which you need
They do almost the same work. What differs is what you pay with, how long it lasts, and who carries the risk if it goes wrong.
The work is nearly identical. Both roles decide what gets built, choose the architecture, set engineering standards, and sit in the room when a technical decision has commercial consequences. What differs is the deal.
The real difference
A fractional CTO is capability you rent. You pay a fee, you get technical ownership at an agreed cadence, and either side can end it with notice. If the company fails, they’ve still been paid for the days they worked.
A technical co-founder is capability you buy with a share of the company. They take equity and carry your risk alongside you, and if the company fails they have nothing to show for the years.
| Fractional CTO | Technical co-founder | |
|---|---|---|
| You pay with | Fees | Equity, 20–50% in most deals I’ve seen |
| Ends when | Either side gives notice | Vesting finishes, or a leaver clause bites |
| Carries your risk | No | Yes |
| Reversible | Yes | Only if you set it up to be |
| Right when | You know roughly what you need | You’re still working out what the company is |
The question that separates them
Do I need someone to own the technology permanently, or do I need someone to own it now?
Most founders who ask me need it now. They have a business, or the clear shape of one, and they need someone senior to make a series of decisions over the next few months and be accountable for them. That’s a fee, and a fee is far cheaper than equity for that job.
A smaller number need a co-founder. The tell is that they can’t yet describe what the company builds, and answering that needs someone technical inside the business for years, taking the same downside as everyone else.
If you can write a coherent brief, you don’t need to give away half your company to have it executed.
What equity really costs
Founders underestimate this because they price it against today’s valuation, and today’s is low, or notional.
Twenty per cent of a company that exits at £5 million is £1 million, for a role that as a retainer might have cost £60,000 a year. If the engagement lasts two years and the company takes six to exit, you paid roughly eight times the market rate.
Vesting stops that arithmetic being automatic, and it’s the part founders skip. Standard UK terms put a founder’s equity on a vesting schedule with good and bad leaver provisions, so someone who leaves in year two keeps a slice of the grant. It’s normal and cheap to draft. Get it agreed before anyone signs, because nobody has ever cheerfully agreed to it afterwards. The norms I know are UK ones.
None of that’s an argument against co-founders. Sometimes the alternative is no company at all. It’s an argument against reaching for equity because it feels free on the day you sign, and you’ve got one lot of equity to give away.
I’ve had investors on a cap table and taken them off again, and the second part is far harder than the first. Whoever you give equity to, you marry their circumstances as well as their contribution: their divorce, their next job, their view in three years about whether they still got a fair deal, and the fact that they’ll still be on the cap table the day you’re raising and an investor asks who this person is and why they hold a fifth of the company.
The middle, where most engagements land
Every engagement I’ve taken started as a fixed fee. Where equity came into it, the client raised it afterwards, once a fee had shown the work was worth having.
So if you’re considering equity, consider it second. Start with a scoped, paid piece of work, small enough that being wrong about each other is cheap. If it doesn’t work out, you lost a few weeks and some money instead of a fifth of your company.
Which one you need
You need a fractional CTO if: you can describe what the business does; the technical decisions are the blocker; you have budget or can get it; and you’d like to be able to change your mind in six months.
You need a technical co-founder if: the product question is open; you can’t pay a market rate and won’t be able to for some time; the technology is the company; and you’re prepared to run the search for as long as it takes.
You need neither if: the spec is written and you want it built, which is a development team’s job.
Why the search is hard
Good ones are scarce. The people best suited to being a technical co-founder are the people with the most options: a senior salary, their own consultancy, founding something themselves. Persuading one to take your risk instead needs an unusually compelling business or an unusually strong existing relationship, which is why so many founders who start out looking for a co-founder end up hiring a fractional CTO.