A full-time CTO in London costs £130,000 to £180,000 in base salary. Add equity, employer NI, pension, benefits, and the recruiter fee that got them through the door, and you’re looking at £200,000+ in year one. For a Series A startup or a 30-person agency, that’s a serious number. And the question isn’t whether you need senior technical leadership. You probably do. The question is whether you need it five days a week, 52 weeks a year.
That’s the real decision behind “fractional vs full-time.” It’s not about quality. It’s about fit. The right model depends on your stage, your team, and what you’re actually trying to solve.
This post lays out both options honestly. Where each one works. Where each one doesn’t. And how to figure out which one you need right now.
Table of Contents
- What a Full-Time CTO Actually Does (and Costs)
- What a Fractional CTO Does Differently
- The Real Cost Comparison
- When to Hire Full-Time
- When Fractional Is the Smarter Move
- How to Transition from Fractional to Full-Time
- Frequently Asked Questions
Key Takeaways
- A full-time CTO costs £200k+ in year one when you factor in salary, equity, NI, pension, benefits, and recruitment. A fractional CTO typically runs £2,000 to £3,500 per day, 2 to 4 days a week, with no equity dilution and no notice period.
- Fractional doesn’t mean junior. A fractional CTO brings the same strategic thinking, architecture decisions, and investor credibility as a full-time hire. The difference is the engagement model, not the seniority.
- Full-time makes sense when the CTO role is the product. If your company’s core value is its technology and you need someone embedded in the team every day, hire permanently.
- Fractional makes sense when you need the thinking but not the headcount. Pre-revenue founders, agencies without a tech lead, companies between funding rounds. You get the strategic clarity without the fixed cost.
- The best outcome is often a planned transition. A fractional CTO defines what the permanent role looks like, builds the team, then hands off. That’s not a compromise. That’s a strategy.
What a Full-Time CTO Actually Does (and Costs)
A good full-time CTO does three things: sets technical strategy, builds and leads the engineering team, and translates between the business and the technology. They own the architecture. They own the hiring pipeline. They own the technical narrative when you’re raising money or pitching a client.
In London, that role commands £130,000 to £180,000 in base salary, depending on the company’s stage and the candidate’s background. At a seed-stage startup, you might land someone at the lower end. At Series A with 20+ engineers, expect the upper range.
But base salary is only part of the picture.
| Cost component | Typical range |
|---|---|
| Base salary | £130,000 to £180,000 |
| Employer NI (15.05%) | £17,000 to £23,000 |
| Pension (5% employer minimum) | £6,500 to £9,000 |
| Benefits (health, equipment, training) | £3,000 to £8,000 |
| Equity (0.5% to 2% at Series A) | Variable, often £50k to £200k+ in paper value |
| Recruitment fee (20-25% of salary) | £26,000 to £45,000 |
| Year one total (excl. equity) | £182,500 to £265,000 |
That’s before they’ve written a line of code or attended a board meeting. And if it doesn’t work out, you’re looking at a 3 to 6 month notice period, potential settlement costs, and the time and money to run the search again.
None of this means full-time is wrong. It means you should be clear about what you’re buying and whether you need all of it right now.
What a Fractional CTO Does Differently
A fractional CTO does the same job. Architecture decisions, team structure, vendor evaluation, investor conversations, technical due diligence. The difference is the wrapper: instead of five days a week on payroll, it’s typically 2 to 4 days a week on a retainer or day-rate basis.
This isn’t consulting in the traditional sense. A consultant writes a report and leaves. A fractional CTO is embedded in your team. They attend standups (or run them). They review pull requests. They sit in on board meetings. They’re accountable for outcomes, not just recommendations.
The services I offer are structured this way: monthly retainers, typically 2 to 4 days per week, with the flexibility to scale up for critical periods (fundraising, platform migrations, new hires) and scale down when the team is running well.
What you don’t get: someone in the office every day. If your engineers need a manager they can tap on the shoulder at 4pm on a Thursday, a fractional CTO might not be the right fit. But if what you need is the strategic layer, the architecture oversight, and the credibility in the room when it matters, that’s exactly what fractional delivers.
The Real Cost Comparison
Here’s what the numbers look like side by side for a 12-month period.
| Full-time CTO | Fractional CTO (3 days/week) | |
|---|---|---|
| Annual cost | £182,500 to £265,000 | £96,000 to £168,000 (at £2,500/day) |
| Equity dilution | 0.5% to 2% | None |
| Recruitment cost | £26,000 to £45,000 | None |
| Notice period | 3 to 6 months | Typically 1 month |
| Ramp-up time | 3 to 6 months to full effectiveness | 2 to 4 weeks |
| Flexibility to scale | Low (fixed headcount) | High (adjust days as needed) |
| Available from day one | No (search takes 3 to 6 months) | Yes (weeks, not months) |
The cost difference is significant. But cost alone isn’t the deciding factor. The right question is: what do you need the CTO to do, and how many days a week does that actually require?
For most seed-stage startups and agencies under 50 people, the honest answer is 2 to 3 days. The strategic decisions, the architecture reviews, the investor prep, the team mentorship. These are high-value activities, but they don’t fill five days every week. Filling the rest of the week with work that a senior developer could do is an expensive way to keep someone busy.
When to Hire Full-Time
Full-time is the right call when:
The CTO role is the product. If you’re building deep technology (AI infrastructure, fintech platforms, biotech data systems) and the CTO’s daily technical decisions are the company’s competitive advantage, you need them there every day. Fractional can’t replicate that depth of immersion.
You have 30+ engineers. At this scale, the CTO role becomes a full-time management job. Hiring pipelines, performance reviews, architecture governance, cross-team coordination. The operational load alone justifies a permanent hire.
You’re post-Series B. You’ve got the runway. You’ve got the team size. You’ve got the board expectation. At this point, not having a full-time CTO is a red flag for investors.
You’ve already validated the role with a fractional. This is the ideal path. You know what the role looks like because someone’s been doing it 3 days a week for 6 months. Now you can write the job spec from experience, not from a template.
I’m not here to pretend fractional is always the answer. Sometimes you just need someone in the building.
When Fractional Is the Smarter Move
Fractional works when you need strategic technical leadership but the maths doesn’t justify (or your runway can’t support) a full-time executive hire.
Seed to Series A founders. You’ve got a product, maybe a small dev team, and you’re preparing to raise. You need someone who can own the technical narrative with investors, review your architecture, and help you make your first senior engineering hire. You don’t need them five days a week. Here’s how I work with founders at this stage.
Agencies between 10 and 50 people. You’re winning more technical briefs. Enterprise clients are asking about your security posture, your deployment process, your architecture approach. You need credibility in the room and someone to shape the technical operation. But a £200k hire for a 30-person agency is a stretch. Here’s how I work with agencies.
Companies between funding rounds. You’ve closed your seed. Series A is 12 to 18 months away. You need to build the technical foundation that makes the next raise credible, but burning £250k on a CTO before you’ve got the ARR to support it doesn’t make sense.
Organisations mid-transformation. You’re migrating platforms, adopting AI workflows, or modernising a legacy tech stack. You need senior oversight for 6 to 12 months, not a permanent addition to the org chart.
In all these cases, fractional gives you the thinking without the overhead. And when you’re ready to go full-time, the transition is smoother because the role has already been shaped by someone doing it.
How to Transition from Fractional to Full-Time
The best fractional engagements have a built-in exit strategy. Not because the relationship fails, but because it succeeds.
Here’s what that typically looks like:
Months 1 to 3: Foundation. The fractional CTO audits your current setup, defines the architecture direction, establishes engineering processes, and starts building relationships with the team. They’re doing the job and documenting what the job actually requires.
Months 4 to 8: Build. They hire your first senior engineers, set up the technical interview process, implement the tooling and workflows that the team will run on. The “how we build things here” playbook gets written through practice, not theory.
Months 9 to 12: Transition. By now, the fractional CTO has a clear picture of what the permanent role needs. They write the job spec from lived experience. They help you hire. They onboard the new CTO. Then they step back.
This isn’t a failure of the fractional model. It’s the point of it. You get the strategic leadership when you need it most (early, fast, without a six-month search), and you build toward permanent when the business can support it.
Some engagements run longer. Some are shorter. The shape depends on the company. But the principle holds: fractional is a bridge, not a destination. Unless you’re an agency, in which case 2 days a week of senior technical oversight might be exactly the right permanent arrangement.
Frequently Asked Questions
How much does a fractional CTO cost in the UK?
Day rates for experienced fractional CTOs in London typically run £2,000 to £3,500 per day, depending on the complexity of the engagement and the seniority of the person. Most engagements are structured as 2 to 4 days per week on a monthly retainer, putting the monthly cost between £16,000 and £56,000. That compares to £15,000 to £22,000 per month for a full-time CTO’s salary alone (before NI, pension, equity, and benefits).
Can a fractional CTO help raise investment?
Yes. A significant part of the role is owning the technical narrative for investors. That includes articulating the architecture rationale, the scalability plan, the build-vs-buy decisions, and the engineering team roadmap. I’ve supported founders through seed and Series A raises where the technical credibility of having a named, experienced CTO in the deck made a measurable difference.
How many days a week does a fractional CTO work?
Typically 2 to 4 days, though this flexes based on what’s happening. During a fundraise, a platform migration, or a critical hire, it might be 4 days. During steady-state, 2 days is often enough. The flexibility is one of the main advantages of the model.
What’s the difference between a fractional CTO and a technical consultant?
Accountability. A consultant analyses your situation, writes a report, and moves on. A fractional CTO is embedded in your team, accountable for outcomes, and involved in execution. They attend your standups, review code, join board meetings, and own the technical decisions. The output isn’t a document. It’s a functioning technical operation.
When should I stop using a fractional CTO?
When the role has grown into a genuine full-time position and you’ve got the revenue or runway to support it. The fractional CTO should help you recognise that inflection point, write the job spec, run the hiring process, and onboard their replacement. If your fractional CTO is incentivised to stay forever, that’s a misalignment. The goal is to build something that outgrows the fractional model.
Do I need a London-based fractional CTO?
Not strictly, but it helps. In-person time builds trust faster, especially in the early weeks. For agencies pitching enterprise clients, having a named CTO who can sit in the room carries weight that a remote arrangement doesn’t. Most of my work is hybrid: a mix of on-site days and remote, weighted toward in-person during the first few months.