Fractional CTO vs interim CTO — what's the difference?

A fractional CTO works part-time (typically 1–3 days per week) across multiple companies on an ongoing basis. An interim CTO works full-time for a single company for a fixed period, usually 3–12 months. Fractional suits ongoing strategic leadership; interim suits full-time coverage during a gap or transformation.

Interim CTOs typically cost more in absolute terms because they work five days a week at a comparable day rate. A fractional CTO at two days per week at £1,100/day costs roughly £115,000 annually. An interim CTO at the same day rate working full-time costs approximately £264,000. The right comparison is cost per outcome, not cost per day.

Functionally yes — both work reduced hours. "Fractional" has become the preferred industry term because it implies portfolio working (the executive is fractionally engaged across multiple clients), whereas "part-time" can imply a reduced version of a full-time role. The terms are often used interchangeably.

Hire interim when you need someone in the seat full-time: after a sudden CTO departure, during a major technology transformation that requires daily hands-on leadership, or when your engineering team needs a visible daily presence. Hire fractional when you need strategic guidance and senior oversight running alongside the business, without needing that person physically present every day.

Yes, and it is a common pattern — a fractional engagement serves as a low-risk trial period for both sides. If the relationship works and the business grows to the point where full-time technology leadership is warranted, converting the engagement is straightforward. The same applies to interim CTOs transitioning to permanent.

Usually, but not automatically. Fractional CTO engagements are typically structured outside IR35 — the executive works across multiple clients with a statement of work, no mutuality of obligation, and right of substitution. Interim CTO engagements are more variable — high-day-count, single-client, fully integrated engagements are more likely to fall inside IR35. The hiring company makes the determination.

Both are established. Interim executive placements have a longer history in larger UK organisations. Fractional arrangements have grown significantly since 2020, particularly at startup and scale-up stage, as remote working made part-time senior leadership more practical.

Rarely, but it happens — for example, using an interim CTO full-time for a 6-month transformation while a fractional CTO provides ongoing board-level technology governance. In most cases this would be duplication of leadership, not complementary.

Sometimes. At pre-seed and seed stage, fractional CTOs may accept a reduced day rate in exchange for a small equity allocation (typically 0.1–0.5%). Interim CTOs almost never take equity given the fixed-term nature of the engagement.

Most fractional CTO engagements run for 12 months or more, with rolling termination provisions (typically 30–90 days' notice). This is longer than most interim engagements and reflects the ongoing strategic nature of the role. Some fractional relationships last several years as the company scales.