Fractional CTO vs. Full-Time CTO: When to Hire Which
Both options are real. Plenty of startups hire full-time CTOs too early and burn cash on a seat they didn't need yet. Others drag a fractional arrangement past its natural end date because change is uncomfortable. The question isn't "is fractional good?", it's "what does your company actually need right now?" This post gives you concrete criteria to make the call, plus the numbers behind it. No vague "it depends."
Key Takeaways
- The median executive CTO search takes 3–6 months, and the all-in first-year cost of a full-time CTO at Series A in the UK regularly exceeds £270k once you include salary, employer NI, benefits, and search fees.
- Fractional makes strong economic sense pre-Series B with fewer than 25 engineers. You get senior strategic input from week one at £6–16k/month with no equity, no employer NI, and no termination risk.
- The trigger to move to full-time is usually a combination of engineering headcount crossing 25–30, a funding round closing, and complexity that genuinely demands daily executive presence.
What's the Core Difference in What You Actually Get?
The difference is time and embedded context, not skill level. A full-time CTO is in the building every day, present for every standup, every difficult conversation, every 3am outage. A fractional CTO gives you strategic decision-making capacity on a scheduled basis, typically one to two days a week, and owns outcomes within that scope. That distinction determines which model fits your situation.
What Does a Full-Time CTO Actually Cost?
Year one all-in for a UK full-time CTO sits at roughly £225k–£360k, depending on stage. The headline salary is the smallest part of that number. In 2025, UK CTO base salaries sit at around £140k–£160k at seed stage and £170k–£210k at Series A, based on data from Ravio and Sifted (accessed 2026-05).
Add employer National Insurance at 15% (above the £5k secondary threshold, effective April 2025), pension contributions, and standard benefits, and total employment cost rises to roughly £185k–£280k per year. Then add retained executive search at £40k–£80k in the UK.
Equity is the other line item founders often undercount. In Europe, a seed-stage CTO typically receives 2–4% of the fully diluted cap table. At Series A, the typical grant falls to 0.7–1.5%, according to Index Ventures' Rewarding Talent data (accessed 2026-05). At a £40m Series A valuation, 1.5% is £600k of dilution baked into the hire before you've started.
Citation capsule: "At VC-backed businesses, CTOs make an average base salary of £180k across all funding stages," according to Sifted's analysis of UK startup CTO compensation (Sifted, accessed 2026-05). Add employer NI at 15%, pension, benefits, and a retained search fee, and the first-year all-in cost sits well above £250k for most London-based startups.
What a fractional CTO actually does and doesn't do
What Does a Fractional CTO Cost?
Fractional CTOs in the UK charge £1,500–£2,500 per day for typical startup engagements, with the London market at the upper end. In 2025, monthly retainers run £5k–£8k for one day a week and £10k–£16k for two days a week, according to market data from fractional.quest (accessed 2026-05). Annualised, that's £60k–£96k at one day a week and £120k–£192k at two days a week. There's no employer NI. No pension obligation. No benefits package. And critically, no equity grant.
From practice: A Berlin-based Series A fintech I advised was budgeting €220k base for a full-time CTO hire. They hadn't modelled the employer social contributions, the retained search fee, or the 1.5% equity grant they'd need to compete for the right candidate. Fractional at two days a week came in at roughly €160k flat with no dilution, and they had someone operational in week two instead of month six.
What Are the Real Capability Trade-offs?
The median executive search for a senior engineering leader in 2025 takes 3–6 months, with Altios (accessed 2026-05) noting that the 6-month reality is what most companies don't want to hear. That's a 3–6 month gap in technical leadership before a full-time CTO is even at the desk. The honest comparison matters more than the sales pitch for either model.
Full-time advantages are real: daily presence means the CTO can own culture and process evolution in a way that part-time engagement genuinely can't match. They're available at 3am during a production incident. They can manage a large direct team and carry the weight of difficult personnel decisions continuously.
Fractional advantages are also real: zero hiring lag, no termination risk, no equity dilution, and, often underrated, the pattern recognition that comes from working across multiple companies simultaneously. Seeing the same scaling problems at four different Series A companies builds a kind of institutional knowledge that a first-time-in-role CTO rarely has.
When Does Fractional Actually Win?
Fractional is the right call in specific, identifiable situations, not as a permanent hedge. Pre-Series B with fewer than 20 engineers is the clearest case: the engineering org doesn't yet have the management surface area that justifies a full-time exec. Post-CTO departure is another: you need continuity and strategic momentum while you run a proper search, and a fractional CTO can hold the line for 3–6 months without burning equity. Approaching a funding round is a third: CTO-level credibility matters to investors, and fractional gives you that without a permanent hire. Finally, if you have a strong VP of Engineering who doesn't need a manager above them, just strategic support and board-level representation, fractional fits that gap precisely.
What the first 90 days as a fractional CTO actually looks like
When Does Full-Time Win?
A full-time CTO earns their seat at the table when complexity genuinely demands daily executive presence. Series B and beyond, with 30+ engineers growing fast, is the clearest trigger. A CTO can't own an engineering culture they're only present for two days a week when the team is 40 people and scaling. Similarly, if you're building a technically complex product where the CTO needs to make architectural decisions daily, not weekly, the part-time model breaks down. Post-acquisition integration is another case: you need someone fully embedded to drive the technical convergence. At 50+ engineers, the management surface area simply exceeds what a fractional engagement can handle.
The Transition: When to Move from Fractional to Full-Time
The fractional model should be time-bounded. It's a bridge, not a destination. The common trigger for a planned transition is a combination of three things happening at once: engineering headcount crossing 25–30, a Series B closing, and the complexity of daily decisions growing past what two days a week can address. At that point, you hire full-time and a fractional CTO who's done their job well is in the best possible position to help. They know the codebase, the team, the investors, and the strategic context. They can write a genuine handover, run a parallel search, and help you evaluate candidates with the clarity of an insider.
From practice: I've done this transition twice, once at a Frankfurt-based logistics startup, once at a London SaaS company. Both times, the fractional phase ran for around nine months and ended with a full-time hire the team already knew from the fractional CTO's network. The first onboarded in two weeks rather than three months because the groundwork was there. The key: agree at the start that the transition is the goal, not an afterthought.
Engineering strategy that founders can actually use
The Decision Matrix
| Dimension | Fractional CTO | Full-Time CTO |
|---|---|---|
| Monthly cost | £5k–£16k (no equity, no NI) | £16k–£25k + equity + NI + benefits |
| Availability | 1–2 days/week, structured | Full-time, always on |
| Time to value | Week one | 3–9 months (search + ramp) |
| Culture ownership | Limited, strategic, not daily | Full, present every day |
| Team management | Light, often advisory | Direct, org-wide |
| Hiring process | Days to weeks | 3–6 months median |
| Equity required | None | 0.7–4% depending on stage |
| Best stage | Pre-Series B, <25 engineers | Series B+, 30+ engineers |
Frequently Asked Questions
Can a company have both a fractional CTO and a Head of Engineering?
Yes and it's often the best structure for a Series A company that's scaling fast. In 2025, this pairing is increasingly common: the Head of Engineering owns day-to-day delivery and people management, while the fractional CTO handles strategy, board reporting, and external technical credibility. The key is a clear division of responsibility written down from day one. Without it, overlap creates confusion.
How do I find a fractional CTO?
Not LinkedIn cold outreach. The most reliable route is through your existing VC network. Most tier-one European funds maintain relationships with fractional operators. Secondarily, communities like Contra, YC's work network, and engineering leadership forums (LeadDev, CTO Craft) surface experienced operators. Referrals from other portfolio companies at the same stage carry the most signal. Expect to speak with three to five candidates before making a call.
What notice period or contract length is typical?
Standard fractional CTO contracts run three to six months with a 30-day termination clause on either side. In 2024–2025, most engagements in the UK market start with a three-month initial term with a structured review point. This keeps both parties honest about fit and progress. Avoid open-ended arrangements. They create ambiguity about outcomes and remove the healthy pressure of time-boxing.
Can a fractional CTO attend board meetings or investor calls?
Yes, and in many cases this is one of their most valuable contributions. Investors want technical credibility at the table. A fractional CTO with a track record at recognised companies, particularly one who's been on the sell side of a Series B or C, carries real weight in those conversations. Make this expectation explicit in the contract. Some fractionals build it into their standard retainer; others charge separately for board attendance.
When does fractional become more expensive than full-time?
The crossover typically happens at around two to two-and-a-half days per week of consistent engagement. At that point, monthly retainer costs approach the equivalent employment cost of a junior full-time CTO, without the cultural and managerial depth a full-time hire provides. In 2025, if you're consistently using a fractional CTO at more than two days a week for longer than six months, that's a strong signal you need a full-time hire and have been deferring the decision.
The Bottom Line
If you're pre-Series B with fewer than 25 engineers, fractional is almost always the right call. You get strategic leadership from week one, pay only for the time you need, and preserve equity and hiring bandwidth for roles where full-time presence genuinely matters. Past Series B, or when engineering headcount, complexity, and cultural demands all point in the same direction, the calculus shifts and a full-time CTO becomes the right investment. The mistake is not choosing the wrong model. It's staying in the wrong one too long.