The six labels and what they actually mean
UK CFO engagement labels in 2025/26, in rough order of formality:
| Label | Typical meaning | Term | Days/mo |
|---|---|---|---|
| Interim CFO | Full-time-ish, fixed term, covering a gap or transition | 3-12 months | 15-22 |
| Fractional CFO | Part-time, ongoing, multiple days per month, integrated | Open-ended | 2-12 |
| Part-time CFO | Same as fractional in most uses | Open-ended | 2-12 |
| Outsourced CFO | Delivered via a firm/agency; less individual; often bundled with accounting | Open-ended | 1-6 |
| Plug-in / Virtual CFO | Same as fractional, marketing label | Open-ended | 1-8 |
| CFO as a Service | Productised version of outsourced CFO, fixed packages | Open-ended | 1-4 |
Important: these labels are not standardised. Some firms call a 2-day-a-week engagement "interim"; others call the same thing "fractional"; others "part-time". Always look at the contract terms, not the label.
Interim CFO — definition and when it's right
The cleanest definition: an interim CFO is engaged for a defined period (3-12 months) to cover a specific gap or transition, usually at near-full-time intensity (15-22 days/month).
Typical interim CFO triggers:
- Full-time CFO has left; permanent replacement search will take 4-6 months
- Active M&A process; deal close in 6-9 months; current finance team doesn't have execution capacity
- Crisis / turnaround; need rapid hands-on finance leadership for 6 months while issues stabilise
- Pre-IPO or major fundraise; 6-12 months of intensive prep before a longer-term hire
- Maternity/paternity/sickness cover
UK interim CFO day rates in 2025/26: typically £1,500-£2,500/day. At 18-20 days/mo that's £27-50k/mo. Expensive, but appropriate for the workload — interim is genuinely intense.
What you don't use interim for: ongoing fractional support. Interim is by definition time-bounded; using it for open-ended fractional work means paying full-time rates without the full-time integration.
Fractional CFO — definition and when it's right
The cleanest definition: a fractional CFO is engaged on an ongoing basis at part-time intensity (2-12 days/month), integrated into the founder/management team but explicitly not full-time.
Typical fractional CFO triggers:
- £1-25M revenue, ongoing operating cadence (board pack, forecast, KPI review)
- Pre-Series A or Series A through B — workload genuine 4-8 days/mo, not 22
- Specialised expertise needed (SaaS metrics, D2C unit economics, agency utilisation) where a generalist FC won't cover it
- Want CFO-grade input without the full-time hiring cost or commitment
UK fractional CFO retainers in 2025/26: £195-£15,000/month covering 0.5-12 days. See our UK fractional CFO cost guide for the full breakdown.
What you don't use fractional for: a permanent gap that needs full-time presence; a 6-month exit process needing daily attention. Fractional flexes within 2-12 days/mo; outside that band it's a different shape.
Outsourced CFO — definition and when it's right
The cleanest definition: an outsourced CFO is delivered via a firm or service provider rather than as an individual, typically as part of a productised package bundled with accounting, bookkeeping or management accounting.
Typical outsourced CFO triggers:
- Sub-£3M revenue, want predictable monthly cost, less concerned about individual continuity
- Want CFO oversight bundled with bookkeeping and management accounts (single relationship)
- Founder-led business that doesn't need a "personality" at the board level yet
- Geographic or scheduling reasons that make a single individual hard to retain
UK outsourced CFO packages in 2025/26: typically £750-£3,500/month for productised packages. The CFO time tends to be less (1-4 days/mo); the firm covers it with a team rather than a single individual.
Trade-off: lower price, less individual depth, more bundle-friendly — but the relationship is with a firm not a person, and the CFO seniority is usually slightly lower than equivalent independent fractional.
Side-by-side at a glance
| Dimension | Interim | Fractional | Outsourced |
|---|---|---|---|
| Term | 3-12 months | Open-ended | Open-ended |
| Days/mo | 15-22 | 2-12 | 1-4 |
| Cost/mo (UK 2025/26) | £27-£50k | £500-£15k | £750-£3.5k |
| Delivered by | Individual | Individual | Firm / team |
| Continuity | Time-bounded | Long-term | Firm-bound |
| Best for | Crisis / transition / M&A | Ongoing scale-up | Sub-£3M revenue / bundled |
What to put in the contract — regardless of label
The contract terms that actually matter:
- Committed days per month — written in numbers. "2 days minimum, up to 4 days at retainer rate" works. "As required" is a red flag.
- Day rate for additional days — what does the 5th day in a month cost?
- Notice period — 30 days for fractional is standard; 60-90 for interim.
- Named CFO (especially for outsourced) — who specifically is doing the work? Can the firm rotate them without notice?
- Scope inclusions/exclusions — what's covered in the retainer vs billed separately. Particularly important for fundraise prep, audit prep, system implementation.
- Termination at convenience clause — either side, 30 days' notice, no penalty. A firm that won't accept this is fishy.
- IP and confidentiality — standard but check.
- Conflict of interest clause — fractional CFOs often work with 4-8 clients. The contract should require disclosure of conflicts (competitors, related sectors).