Interim CTO vs Fractional CTO: Which Does Your Business Need?

"We need a CTO" is one of the most common things we hear from scaling businesses. It is also one of the least specific. A full-time CTO, an interim CTO, and a fractional CTO are three fundamentally different solutions to three different problems. Choosing the wrong one wastes money and time.

This guide explains the real differences, what each costs, and how to decide which model fits your situation.

The Core Difference

The distinction is simpler than most articles make it.

An interim CTO is a full-time, temporary appointment. They work five days a week, typically for three to six months, filling a gap during a transition. Think of them as a locum in medicine. Your CTO left unexpectedly. You are in the middle of a critical platform migration. You need someone in the seat now, full-time, until you find a permanent replacement.

A fractional CTO is a part-time, ongoing appointment. They work one to three days per week, typically for 12-18 months or longer. They are a permanent part of your leadership team, just not a full-time one. They provide strategic direction, build capability in your team, and ensure technology decisions align with business objectives.

The deciding factor is not "which is better" but "what does your business actually need right now?"

Cost Comparison

The financial difference is significant.

Interim CTO: £10,000-£15,000 per month (full-time). Some charge day rates of £1,200-£2,000. Over a typical six-month engagement, total cost is £60,000-£90,000.

Fractional CTO: £3,000-£10,000 per month (one to three days per week). Over a typical 12-month engagement, total cost is £36,000-£84,000.

Full-time permanent CTO: £150,000-£300,000 per year including salary, employer NI, pension, benefits, and recruitment fees.

The maths is straightforward, but the cost comparison only tells part of the story. The real question is what value you extract from the investment. An interim CTO who stabilises a crisis and saves a failing project is worth every penny. A fractional CTO who transforms your technology strategy and saves you from a bad acquisition is equally valuable. The wrong choice, however, is always expensive.

When You Need an Interim CTO

Interim CTOs make sense in a small number of specific scenarios.

Your CTO has left suddenly and you need immediate cover. The engineering team needs someone to report to. Decisions are stacking up. Client commitments are at risk. You need a full-time presence to keep the ship steady while you recruit a permanent replacement.

You are in the middle of a crisis. Production is down regularly. Three senior engineers quit last month. A security breach has exposed systemic problems. These situations demand full-time, hands-on leadership.

You are going through a major transformation that needs daily oversight. A complete platform migration, a post-merger integration, or a fundamental re-architecture of your technology stack. These are intensive projects that require a CTO to be present and available every day.

You have a time-bounded, full-time need. Due diligence preparation for an imminent exit, a regulatory deadline that requires intensive technology remediation, or a rapid scaling phase where you are hiring 20 engineers in three months.

The common thread is urgency, intensity, and a defined end point. If your need does not have all three characteristics, you probably need a fractional CTO instead.

When You Need a Fractional CTO

Fractional CTOs are the better fit for the majority of mid-market businesses. Here is why.

You need strategic leadership, not daily operational management. Most mid-market companies do not generate 40 hours of CTO-level work each week. They need someone to set direction, make the big calls, and ensure quality, but the day-to-day management can be handled by a senior developer or engineering manager.

You want to build internal capability, not create a dependency. A fractional CTO can mentor your tech lead, improve your engineering processes, and build the team's ability to operate independently. An interim CTO, by design, fills a gap rather than building long-term capability.

Your need is ongoing rather than time-bounded. Technology strategy is not a project. It requires continuous attention, adjustment, and alignment with business objectives. A fractional CTO provides this continuity.

Budget matters. At £5,000 per month versus £12,000 per month, the fractional model lets you access senior leadership at a fraction of the cost. For many businesses, that difference represents the salary of a developer who can actually build the things the CTO recommends.

You are not ready for a full-time hire. Perhaps you will need a permanent CTO in 18 months when you hit £40 million in revenue. A fractional CTO bridges that gap, and can even help you hire their replacement when the time comes.

The Expensive Mistakes

We see the same errors repeatedly.

Hiring an interim when you need a fractional. The most common mistake. A business feels the urgency of not having a CTO and hires an interim at £12,000/month. Three months in, they realise the need is strategic and ongoing, not operational and temporary. They have spent £36,000 and still do not have a long-term solution.

Hiring a fractional when you need an interim. Less common, but equally costly. Your CTO left during a critical platform migration. You bring in a fractional at two days per week. They are not available when production goes down on Wednesday, they miss the context of conversations that happen on days they are not there, and the team feels leaderless. You need someone full-time until the immediate crisis passes.

Confusing either role with a technical consultant. If you need someone to solve a specific technical problem (migrate from AWS to Azure, implement a particular integration, audit your security), you need a consultant, not a CTO. Consultants are project-scoped and often more cost-effective for defined technical work.

Expecting a fractional CTO to write code. If your job description includes "hands-on coding," you are looking for a senior developer with some strategic capability, not a CTO. Fractional CTOs make decisions, build teams, and set direction. They do not sit in your codebase writing features.

Making the Decision

A simple framework.

Ask yourself three questions. First, is the need urgent and intensive, requiring someone five days a week? If yes, start with an interim and transition to fractional or permanent once the crisis passes. Second, is the need strategic and ongoing, requiring one to three days of senior input per week? If yes, hire a fractional CTO. Third, is the need specific and time-bounded, like a particular technical project? If yes, hire a technical consultant.

Many businesses use a combination. An interim CTO to stabilise a crisis over three months, transitioning to a fractional CTO for ongoing strategic leadership. This is a legitimate and often sensible approach.

How Boardman Helps

Boardman provides fractional CTO, CIO, and CISO services for UK mid-market businesses. We do not provide interim placements because our model is built around long-term, retained relationships where we can drive genuine strategic change.

If your situation genuinely requires an interim CTO, we will tell you that and can recommend partners who specialise in interim executive placements. We would rather point you in the right direction than sell you something that does not fit.

For businesses that need ongoing strategic technology leadership, our fractional CTOs embed into your organisation, attend your leadership meetings, and take real ownership of your technology strategy. Engagements typically run 12-18 months, because meaningful change takes time.