The short answer: an interim executive holds a seat full-time for a defined period — a departure, a turnaround, a transaction sprint. A fractional executive owns a function part-time on an ongoing basis. The test is two questions: is the need bounded or ongoing, and does it demand full-time presence or senior hours?
The definitions, precisely
Interim means full-time and temporary. The executive is the CFO (or COO, or CTO) for six to twelve months, embedded daily, usually through a transition with a beginning and an end: a sudden departure, a post-acquisition integration, a carve-out, the run-up to a sale.
Fractional means part-time and ongoing. The executive owns the function at ten to twenty hours a week, typically alongside one or two other clients, with no built-in end date — the engagement runs as long as the work does.
The decision table
| Your situation | The right model |
|---|---|
| CFO resigned mid-audit; the seat can’t sit empty | Interim |
| Founder still owns finance; needs senior discipline, not 50 hrs/week | Fractional |
| Post-acquisition integration with a 9-month plan | Interim |
| First sales team, pricing overhaul, ongoing GTM ownership | Fractional |
| Getting numbers diligence-ready before a sale | Interim (often an ex-Big 4 audit-leadership profile) |
| Function is real but stage will outgrow a full-time hire | Fractional |
Where people get it wrong
Using fractional to avoid a hard call. If the workload is honestly full-time, splitting it into fractional hours delays the problem. Interim-then-permanent is the honest sequence: stabilize the seat now, run the real search at the pace it deserves.
Using interim for an ongoing need. An interim engagement without a defined end becomes an expensive full-time hire without the commitment. If you can’t say what “done” looks like, the need is probably fractional or permanent.
Assuming the same bench serves both. The profiles differ. Fractional work rewards operators who run portfolios well; interim transitions — especially transaction-readiness — often want ex-Big 4 senior-level executives and senior operators who have carried that specific weight before.
Deciding for your company
Write down two answers: when does this need end? and how many senior hours does it truly require weekly? Bounded + full-time points to interim; ongoing + partial points to fractional. If the answers argue with each other, that ambiguity is exactly what a discovery call is for.