You know you need senior technical leadership. You're just not sure what form it should take. Full-time CTO with equity? An advisor? A consultant who drops in for a week? A fractional CTO a day or two a week?
Each model exists because each one solves a different problem. And picking the wrong one is expensive.
The full-time CTO
This is what most people think of when they think "CTO." A senior engineer as a full-time hire, usually early enough to get equity, reporting directly to the founder.
When it works: You're pre-seed to Series A, you have a technical co-founder or you're non-technical and need someone to own the entire build from scratch. You're willing to give equity because you're betting on the person for years. You need someone embedded in the culture, in on every decision, building the team alongside you. The person is hungry and believes in your vision.
When it doesn't: You're not 100% sure what you're building yet. You hire someone and three months later the product direction changes and they're doing something different from what they signed up for. Or you're at Series B+ with 15 engineers and a VP of Engineering already; giving another full-time senior person to the structure is overhead. Or the person leaves and suddenly you're orphaned and you realize they made all the decisions and nobody else knows why anything is the way it is.
The cost: £120k–£200k salary, equity (10–5% depending on stage), benefits, recruitment risk, all-in cost about £160k–£250k per year if they stay. But sunk cost if they leave in year two.
The advisor
Someone senior who sits on your board or meets with you monthly, gives advice, makes introductions, lends credibility. Sometimes they're paid a small amount (£500–£1,500 a month); often they're not.
When it works: You need strategic guidance, not daily execution. You have an experienced operator in-house already and you want someone who's been through it to sanity-check big decisions. You need an introduction to their network or their name on your about page. You need occasional wisdom, not daily hands-on help.
When it doesn't: You need accountability. An advisor is free to leave whenever, takes zero responsibility for outcomes, and shows up when they feel like it. If you have a technical problem that needs solving, they're not the right person. If you're early and need someone who's in the trenches, you'll be frustrated.
The cost: £0–£20k per year if paid; a percentage of equity if you really want them, but often just prestige and relationship.
The consultant
Someone senior who comes in, usually for a defined window (2 weeks to 3 months), assesses what you need, produces a report or strategy, and leaves.
When it works: You have a specific problem: "Should we rebuild our API?", "What should our architecture look like?", "Do we have a security gap?", "Is this database choice a mistake?" They come in, you get a clear answer, they leave. You have the information; your team executes on it.
When it doesn't: You think they'll stay accountable for the answer. They won't. A consultant hands you a report about what you should do; they don't stick around to make sure it actually happens. If the engineering team disagrees with the recommendation, the consultant is gone and you're left mediating. Also, if your problem is "nobody's making decisions," a consultant will write you a very clear report about what you should do. But they won't *be there* when you need to pick between two hard options at 4pm on a Friday.
The cost: £3k–£8k per week, usually 4–8 weeks, so £12k–£64k per engagement.
The fractional CTO
Someone senior who commits to a regular schedule (usually 1–3 days a week), owns technical direction, stays accountable for outcomes, and stays hands-on on the work. Usually structured as a monthly retainer.
When it works: You're Series A–B, or you're well-funded pre-seed and growing. You need someone senior making technical decisions regularly, but not full-time (because your product is mostly defined, or you have other senior engineers, or you don't have the cash for a full-time salary). You need them accountable for what ships, not just giving advice. You want them writing code or deeply reviewing it so they understand what the team is fighting against. You need the decisions made *regularly* (not in one burst of consulting, not in an occasional board meeting).
If you're still getting clear on the role itself, this article explains what a fractional CTO actually does.
When it doesn't: You're still pivoting rapidly; you need someone in the building full-time. Or you're early enough that you need equity-level commitment and a person who's betting their career on your success. Or you have no engineering and need someone to teach your first hires how to build; a fractional person isn't available enough for that.
The fractional model works because it matches the problem: regular leadership, not constant overhead. Accountability, not advice-giving. Hands-on, not detached.
The cost: £2,500–£5,000 per month (UK market, varies by experience and complexity), so about £30k–£60k per year, but with far less employment risk than a full-time hire.
How to pick
Ask yourself three questions:
1. Is this a one-time decision or ongoing? If it's a single problem to solve ("audit our architecture," "is our stack right?"), hire a consultant. If it's ongoing ("who decides on database choices, architecture, tech direction?"), you need someone regular: fractional CTO or full-time.
2. How much execution are they going to do? If they're just steering and advising, a fractional CTO or advisor is fine. If you need them deep in the code building things, you probably need full-time or you need to hire engineers separately and the fractional person oversees them.
3. What stage are you at, and how much cash do you have? Pre-seed and non-technical founder: probably full-time CTO with equity, or a hybrid (part-time CTO + your own learning). Series A with other engineers: fractional CTO. Series B+ with multiple senior engineers: advisory board, full-time VP of Engineering, or fractional CTO for specific problems. Pre-revenue but funded: depends on urgency. Post-revenue but early: fractional often makes sense.
The honest overlap
The best fractional CTOs do what the best consultants do (solve hard problems), what the best advisors do (point you in the right direction), and what the best full-time CTOs do (stay accountable and write code). They're just part-time and structured around your cash and your need.
If you know you need someone senior making technical decisions, and you know it's going to be regular, and you don't need someone full-time, fractional is usually the move.
And if your current issue is repeated engineering missteps, read why startups fail at technical decisions for the root causes to look for first.
If you're trying to figure out which model fits your situation, send me a message. Tell me where you are, what decisions are stuck, what your burn rate looks like. I'll tell you honestly whether fractional makes sense, or whether you need something else.