The complete UK guide
Fractional CTO
What a fractional CTO does, what one costs in the UK, when you actually need one, and how to choose well. No sales pitch until the end, and it is clearly marked.
Written by the Prodevel team · Updated July 2026 · 12 min read
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What is a fractional CTO?
A fractional CTO is a senior technology leader who works with your company part time, usually 2 to 6 days a month, on an ongoing retainer. The "fractional" part means you share their time with a small number of other companies. In exchange, you get someone who has run engineering teams before, at a price a seed-stage company can pay.
The role sits between two things you might already know. A consultant parachutes in, writes a report, and leaves. A full-time CTO costs £120,000 to £180,000 a year in London before equity, and takes three to six months to hire. A fractional CTO is embedded like the full-timer and affordable like the consultant: they join your Slack, attend your standups when it matters, and carry responsibility for technical decisions week after week.
The model has grown in the UK since around 2020, mostly because the maths works. A startup with five engineers does not have full-time CTO problems. It has two days a month of CTO problems, and 28 days of engineers needing to get on with the work.
What they actually do
The title sounds vague because the scope adapts to your stage. These six areas cover most of the real work:
Architecture decisions
Reviewing designs before they become expensive mistakes. A wrong database choice at 10 users is a Tuesday afternoon fix. At 10,000 users it is a three-month migration.
Hiring
Writing job descriptions that attract the right engineers, designing interview loops, sitting in on final rounds, and sanity-checking offer packages against the market.
Vendor and agency oversight
One technical voice when you have an agency, two freelancers, and an internal developer all pulling in different directions. Someone who reads the pull requests, not just the invoices.
Roadmap and prioritisation
Translating business goals into a technical plan the team can execute, and saying no to features that sound good in a board meeting but cost six weeks.
Investor and board Q&A
Credible answers on security, scalability, and technical risk when investors run due diligence. Founders lose deals over vague answers here.
Build vs buy calls
Knowing when off-the-shelf is fine, when to build, and when the honest answer is "neither, yet".
Notice what is not on the list: writing code. Some fractional CTOs code a little, and at very early stages that can help. But if you mainly need someone typing, you need a senior engineer, which is a different and cheaper hire.
When you need one (and when you don't)
Founders rarely wake up thinking "I need a fractional CTO". They wake up thinking one of these:
- →You raised a seed round and investors are asking who owns the technology. Right now the answer is "our agency", and everyone in the room knows that is not an answer.
- →You are a non-technical founder and your development agency sets its own deadlines, marks its own homework, and explains every delay with jargon.
- →You have three to eight engineers and no one owns architecture. Every developer makes locally sensible decisions that add up to a mess.
- →Technical due diligence is coming, for a funding round or an acquisition, and you do not know what they will find.
- →The product works but keeps breaking, and you cannot tell whether you need better engineers, better process, or a rebuild.
When you don't need one
An honest provider will tell you this on the first call. You probably do not need a fractional CTO if:
- ✕You have a strong technical co-founder who has scaled a team before. You need peers and advisors, not a fractional CTO.
- ✕You are pre-product and still validating the idea. A one-off session, like a CTO Strategy Day, answers your questions for a fixed fee without a retainer.
- ✕You need hands-on-keyboard development capacity. A fractional CTO leads; if nobody is writing the code, hire developers first.
- ✕You want someone to blame. A fractional CTO with two days a month cannot own outcomes your full-time team controls the other 28 days.
What one costs in the UK
UK pricing in 2026 clusters around four models. The ranges below reflect what we see in the market, not just our own rates:
| Model | Typical range | Notes |
|---|---|---|
| Monthly retainer | £1,500–£6,000/month | The standard model. 2–6 days per month, ongoing. Most UK providers, including Prodevel, price here. |
| Day rate | £800–£1,500/day | Ad hoc or project-scoped work. Flexible, but you lose the continuity that makes the model work. |
| Equity + reduced cash | Varies | Some fractional CTOs take 0.5–2% equity for a lower retainer. Common at pre-seed; read the vesting terms carefully. |
| Full-time CTO (for comparison) | £120,000–£180,000+ base | Plus equity (1–4%), employer NI, pension, and recruitment fees. Add a 3–6 month hire cycle. |
A useful way to read this: the top fractional tier, at £6,000 a month, costs less than half the salary alone of a full-time hire, with no equity, no notice period, and no recruitment fee. The trade-off is time. If your company genuinely needs 15 days a month of technical leadership, the fractional model stops making sense, and a good fractional CTO will say so.
Fractional vs full-time vs interim vs consultant
| Role | Time | Typical cost | Best for |
|---|---|---|---|
| Fractional CTO | 2–6 days/month, ongoing | £1,500–£6,000/mo | Startups that need continuous senior leadership but not a full-time seat |
| Full-time CTO | Full time | £120k–£180k+/yr plus equity | Series B+ with a large engineering org and daily leadership needs |
| Interim CTO | Full time, fixed term | £700–£1,200/day | Covering a departure or leading a defined transition, typically 3–9 months |
| Technical consultant | Project-based | £150–£300/hr | A specific question: an audit, an architecture review, a second opinion |
We wrote a longer comparison of the first two options, with stage-by-stage guidance from pre-seed through Series A, in Fractional CTO vs full-time CTO: UK startup guide.
How engagements work
Details vary by provider, but a well-run engagement follows a recognisable shape. Here is how the first months typically play out:
Weeks 1–2: audit
Codebase review, infrastructure walkthrough, and conversations with every engineer and vendor. The output is a written picture of where you actually are, which is usually different from where you thought.
Weeks 3–6: quick wins and cadence
Fixing the things that are cheap to fix and expensive to ignore: deployment pipelines, code review practice, security basics. A working rhythm gets established with the team.
Month 2 onwards: steady state
A regular cadence of strategy sessions, architecture reviews, hiring support, and board updates. Async access between sessions for decisions that cannot wait.
Contracts usually carry a 3-month minimum and then run month to month with 30 days' notice. Be wary of anyone asking for a 12-month lock-in; the whole point of the model is that it flexes with your stage.
How to choose one
Most founders have never hired for this role, and the people selling it interview well. Five questions that separate operators from talkers:
- Walk me through a technical decision you got wrong. What did it cost, and what changed afterwards?
- How many clients do you work with right now? What happens when two of us have a crisis in the same week?
- What would make you tell me I do not need you any more?
- Show me a board update or technical audit you have written (redacted is fine).
- Have you worked with a team at our stage and stack, or one stage ahead of us?
Red flags
- ✕They recommend a rebuild in the first meeting, before reading any code.
- ✕They cannot name a client they told "you do not need me".
- ✕Everything is a retainer; there is no smaller way to test the fit.
- ✕They talk about technology choices but never ask about revenue, runway, or customers.
- ✕No written deliverables. If the thinking only exists in calls, you are renting a conversation.
Keep reading
Deeper dives on the decisions this guide touches:
Fractional CTO vs full-time CTO: UK startup guide
Real costs, commitment, and stage fit from pre-seed through Series A.
Read the articleChoosing a software agency: 12 questions to ask
How to vet the people building your product, whether or not you hire a CTO.
Read the articleHow to evaluate software development proposals
A UK buyer’s guide to reading quotes, spotting padding, and comparing bids.
Read the articleThe true cost of technical debt
Why shortcuts today kill tomorrow, and how to measure the damage.
Read the articleBuilding high-performing engineering teams
Culture, process, and tools that actually move delivery speed.
Read the articleThe true cost of bad software
Why cheap development costs more, with the numbers to prove it.
Read the articleCommon questions
What does "fractional" mean in fractional CTO?
You get a fraction of a senior technology leader’s time, typically 2 to 6 days a month, on an ongoing retainer. They stay embedded in your business week to week, unlike a consultant who delivers a report and leaves.
How much does a fractional CTO cost in the UK?
Monthly retainers run £1,500 to £6,000 depending on days per month and seniority. Day rates run £800 to £1,500. A full-time London CTO costs £120,000 to £180,000 in base salary plus equity, employer NI, pension, and recruitment fees.
How many days a month do I need?
Most companies under 10 engineers do well on 2 to 4 days a month. Teams of 10 to 20 engineers, or companies heading into due diligence, usually need 4 to 6. If you consistently need more than 6, you are approaching the point where a full-time hire makes sense.
What is the difference between a fractional CTO and an interim CTO?
An interim CTO works full time for a fixed term, usually covering a departure or a defined transition. A fractional CTO works part time indefinitely. Interim is a bridge; fractional is an operating model.
Can a fractional CTO help with investor due diligence?
Yes, and this is one of the most common reasons founders hire one. They prepare documentation, fix the issues diligence will find, and sit in the room to answer technical questions credibly.
How long do engagements last?
Prodevel engagements have a 3-month minimum, then run month to month. In practice most last 6 to 18 months: long enough to fix the foundations and hire the team that replaces the need.
The clearly marked sales pitch
Two ways to work with us
If you want the ongoing model, our fractional CTO engagements start at £1,500/month. If you want to test the water first, a CTO Strategy Day gets you a senior CTO's full attention for one day, with a written 90-day plan, for a fixed £3,500.
Book a discovery callFree 30 minutes. We will tell you honestly if you do not need us.