The CFO Hiring Decision: Fractional, Interim, or Full-Time

The 'when should we hire a full-time CFO?' question arrives in our inbox at least once a week, almost always from a founder who already knows that the answer is 'not yet' but is looking for permission to wait. The harder question — and the one we end up addressing — is which finance function the company actually needs in its next twelve months, and which of the three available structures (fractional, interim, full-time) best delivers it.

The decision has become more nuanced as the fractional CFO market has matured. A senior fractional CFO with the right sector experience now delivers most of what a £200k full-time hire would deliver at £4k–£8k per month, with the asymmetric advantage that the fractional has worked across twenty companies in the past five years rather than one. The trade-off is bandwidth: a fractional is not in the building every day, and there are problems that genuinely require daily presence.

A fractional CFO is hired to solve the strategic gap: the company needs board-grade financial leadership, investor-grade reporting, and capital-strategy guidance, but does not yet need that leadership in the building every day. The work is typically two days a month of board pack preparation, one day a week of finance-team supervision and CEO partnership, and a tight engagement around fundraising or M&A events. The fractional brings the experience of a senior CFO at a fraction of the cost and almost none of the recruitment risk.

What the fractional does not do is run the daily close, supervise the AP team, or sit in every operational meeting. The structure assumes a competent financial controller is in place to handle the operational layer, with the fractional providing the strategic and external-facing layer above it. Companies without that controller — typically below £3m revenue — often discover that the fractional cannot operate effectively without a stronger ground game, and the right hire is the controller first.

The interim CFO is the right structure for a defined event with a defined timeline: a fundraising round, an exit preparation, a system migration, a turnaround. The interim is a senior, full-time presence for six to nine months who is explicitly not the long-term hire, and the brief is to deliver a specific outcome and hand over to a successor. The economics work because the interim is paid at a premium daily rate but for a finite period, and the alternative — hiring a full-time CFO under time pressure for a defined event — usually produces a worse hire.

The mistake to avoid is using the interim as a way to defer the long-term decision. An interim who lingers past the original brief becomes either the de facto full-time CFO (without the benefits of a proper recruitment process) or a source of friction (as the team starts to wonder who is actually in charge). The discipline is to start the long-term recruitment in parallel with the interim engagement, so the handover happens cleanly at the end of the brief.

Above roughly £25m revenue, or in any company preparing for a Series C or beyond, a full-time CFO is non-negotiable. The bandwidth required for investor management, board governance, treasury, tax structuring, and the strategic partnership with the CEO simply exceeds what a fractional can deliver. The full-time CFO is also the person who builds and leads the finance function — typically eight to fifteen people at that scale — and that leadership requires presence, not visits.

The other threshold for the full-time hire is complexity rather than revenue: multi-entity, multi-currency, multi-jurisdiction businesses develop a complexity profile that requires daily senior attention regardless of headline revenue. A £15m business operating in five jurisdictions with three product lines and two regulatory regimes probably needs a full-time CFO; a £40m business operating in one jurisdiction with one product line and one customer segment probably does not.

A full-time CFO at a growth-stage UK or US company is a £200k–£350k base salary plus equity, plus the cost of the recruitment process and the onboarding ramp. A senior fractional CFO is £4k–£12k per month with no equity, no recruitment cost, and an immediate start. The cost differential is four to six times. The experience differential — and this is the part founders rarely model — is often zero, or in the fractional's favour, because the fractional has the option to work across multiple companies and accumulates a broader and more current set of patterns than any single CFO career produces.

The argument for the full-time hire is bandwidth, presence, and long-term ownership. The argument against is cost, recruitment risk, and the opportunity cost of locking in one person's experience. The right answer depends on which side of those trade-offs the company's specific situation falls on, and the answer is rarely permanent — it should be revisited every twelve months as the company evolves.

When a full-time CFO hire does fail, the failure is usually visible in the first six months and the cost is typically twelve to eighteen months of compounded damage: the senior hires the CFO made, the systems the CFO chose, the investor relationships the CFO built. The cost of a failed CFO hire at a £15m company is materially larger than the cost of the salary itself, and the recovery typically requires an interim followed by a second full-time search.

The mitigation is to keep the fractional in place during the first ninety days of a new full-time CFO. The fractional becomes a sounding board for the new hire, accelerates the onboarding, and provides an early-warning system if the hire is not landing. The incremental cost is small, the optionality is large, and the new CFO almost always welcomes the support.

The CapMaven CFO Diagnostic answers this specific question in a structured ninety-minute conversation: where the business is on the revenue and complexity scale, what the next twelve months require, which structure best delivers it, and what the sequencing should be if the answer is to evolve the structure over time. The output is a one-page recommendation with the budget envelope, the role specification, and the search-or-engagement timeline. If you are within six months of needing to make this decision, the diagnostic is the right starting point.