The difference is the calendar. An interim CFO works full-time, usually for three to nine months, to fill a gap. A fractional CFO works part-time, usually one or two days a week, with no planned end date. Both are senior finance executives, and many people do both kinds of work at different points in their careers.
When an interim CFO fits
An interim fits when the job needs a full week and a defined end. The common cases: your CFO resigned and the search will take four to six months; a lender or investor needs a turnaround plan fast; an acquisition closed and two finance teams need to be merged; or an audit found problems that need someone in the building every day. The interim keeps the seat warm, fixes what is urgent and hands over to the permanent hire.
When a fractional CFO fits
A fractional fits when the company needs CFO judgment every month but not CFO hours every day. That describes most companies between $2M and $20M in revenue. The fractional CFO builds the forecast, runs the close review, manages the bank and investors, and stays for years. The value grows with time, because the CFO learns the business and the numbers become comparable from one year to the next.
What each costs
Interim CFOs are priced like a full-time executive for a short period. Expect roughly $15,000 to $35,000 a month, or $1,200 to $2,500 a day, often through a staffing or interim firm that adds its margin. Fractional CFO retainers run $3,000 to $12,000 a month. Over a year, an interim at $25,000 a month costs $300,000; a fractional at $7,000 costs $84,000. The interim is the more expensive option per month and the cheaper one when the need is genuinely temporary.
Check the conversion terms with interim firms. Many charge a fee if you hire the interim permanently.
The private equity case
After a buyout, PE firms often install an interim CFO for the first 100 days to set up the reporting the fund needs: monthly flash numbers, covenant tracking, a budget against the investment case. Smaller portfolio companies then move to a fractional CFO for the hold period, because a $10M company rarely needs a $300,000 executive. PE-backed buyers should look for CFOs who have worked to a fund’s reporting calendar before.
The exit case
Preparing to sell runs on two clocks. Two to three years before a sale, a fractional CFO is usually the better fit: clean books, a consistent monthly close, normalized margins and a history of hitting the forecast are what a buyer pays for, and they take time. In the final four to six months, during the process itself, the workload can become full-time. Data room requests, quality of earnings questions and working capital negotiation pile up. Some fractional CFOs increase their hours for that stretch; others bring in an interim with deal experience.
How to choose
Ask how many days a week the work needs for the next six months, and whether the need ends. Full-time and ending points to interim. Part-time and ongoing points to fractional.