You've got a growing startup, a bank balance that swings month to month, and an investor who wants a proper financial model by Friday. So do you need a fractional CFO, an accountant, or both? It's one of the most common questions we get from UK founders, and the answer isn't "whichever costs less".
These are two different jobs. An accountant keeps the score and keeps you compliant. A CFO helps you decide what to do next with the money. Hire the wrong one for your stage and you'll either overpay for strategy you can't use yet, or fly blind into a fundraise.
This guide explains what each role really does, when a fractional CFO earns its keep, and a simple way to decide. We've written it for early-stage and scaling UK companies, with a worked cost comparison and clear decision steps.
What is the difference between a fractional CFO and an accountant?
The simplest way to put it: your accountant tells you what happened, and your CFO helps you decide what happens next.
An accountant is backward and present looking. They record transactions, prepare your statutory accounts, file your Corporation Tax return, run payroll and keep you compliant with HMRC and Companies House. The work is precise, deadline-driven and largely non-negotiable.
A fractional CFO is forward looking. They build the cash forecast, pressure-test the budget, model your runway, prepare board packs and stand next to you in front of investors. "Fractional" just means part-time: you get a senior finance leader for a day or two a week, or a set number of hours a month, instead of a full-time hire.
Both matter. They're complementary, not competing. The real question is which one your business needs now, and that depends almost entirely on your stage.
What does an accountant do for a startup?
For most UK startups, the accountant is the first finance hire (often outsourced) and the one you can't do without. The core work covers compliance and record-keeping:
- Bookkeeping so your numbers are accurate and up to date.
- Year-end statutory accounts filed with Companies House.
- Corporation Tax returns and computations.
- VAT registration and returns once you cross the threshold.
- Payroll and PAYE for your team, including any directors on salary.
- Self Assessment for directors where needed.
This is the foundation. Without clean books, any forecast a CFO builds is guesswork. If you're a newly incorporated company, our guidance for limited companies walks through what you're legally on the hook for, and our statutory accounts and Corporation Tax services cover the filing side.
A good startup accountant does more than tick compliance boxes. They'll flag when you're approaching the VAT registration threshold of £90,000 (the figure that applies from 1 April 2024), keep your director salary and dividends sensible, and make sure you're claiming the allowances you're entitled to. But strategy, fundraising and forecasting sit outside the typical accountant's remit.
What does a fractional CFO do for a startup?
A fractional CFO is a senior finance leader who joins part-time to handle the things a founder shouldn't be doing at 11pm. The work is strategic and decision-focused:
- Cash flow forecasting and runway management so you know how many months of cash you have and what changes that number.
- Financial modelling for budgets, scenarios and unit economics.
- Fundraising support including the model behind the pitch deck, the data room, and sitting in on investor conversations.
- Board reporting in a format investors and non-executive directors expect.
- Pricing, margin and hiring decisions backed by numbers rather than gut feel.
- Structuring advice on schemes such as SEIS and EIS for investors, EMI share options for staff, and R&D tax relief claims.
That last point is where a CFO and a good tax adviser overlap, and where real money is at stake. The Seed Enterprise Investment Scheme (SEIS), for example, lets a qualifying company raise up to £250,000 from investors, provided it has gross assets of no more than £350,000 when the shares are issued and has been trading for under three years. Getting the structuring right before you raise is far cheaper than fixing it afterwards. Our tax advisory team works alongside founders on exactly this.
In practice, the mistake we most often see is founders hiring a fractional CFO for tasks an accountant should be doing, or trying to fundraise on a spreadsheet held together with hope. Match the role to the job.
When does a startup actually need a fractional CFO?
You don't need one on day one. Most pre-revenue and early-revenue startups are well served by a solid accountant and a tidy spreadsheet. A fractional CFO starts to pay for itself when one or more of these is true:
- You're raising, or about to. Investors want a credible model, clear use of funds and an answer to "what's your runway?". A CFO builds the financial story behind the deck.
- Cash flow is getting hard to predict. Lumpy revenue, growing headcount and longer sales cycles mean a back-of-envelope forecast no longer cuts it.
- You're scaling fast. Hiring, new markets or a step-change in revenue all need someone modelling the downside, not just the upside.
- Decisions now have real financial weight. Pricing changes, a big hire, a new product line: getting these wrong is expensive.
- Your board wants more. Once you have institutional investors, board packs become formal and monthly.
A common trigger point for UK startups is the run-up to a Series A round, when investor expectations rise sharply and the founder's bandwidth runs out. If none of the above is true yet, a fractional CFO is probably premature. Our startups page covers the finance support that fits each stage.
How much does a fractional CFO cost compared with an accountant?
The honest answer is "it depends on scope", but a comparison helps frame the decision. The figures below are illustrative ranges for the UK market to show the shape of the costs, not quotes. Your actual fees depend on your size, complexity and the hours involved.
Illustrative example: a seed-stage UK SaaS startup, around 10 staff
| Option | What you get | Typical engagement | Illustrative annual cost |
|---|---|---|---|
| Outsourced accountant | Bookkeeping, year-end accounts, Corporation Tax, VAT, payroll | Monthly | Lower (fixed monthly fee) |
| Fractional CFO | Forecasting, modelling, fundraise support, board packs | 1 to 2 days a week | Higher than the accountant, far below a full-timer |
| Full-time CFO | All of the above, in-house, full attention | Permanent hire | Highest: salary, employer NIC and benefits |
The point of the fractional model is that you avoid a full-time CFO's cost while still getting senior finance leadership. Remember a full-time hire isn't just salary. As the employer you'd also pay Class 1 employer (secondary) National Insurance at 15% for 2025/26 on earnings above the £5,000 secondary threshold, plus pension and benefits. On a senior salary that adds up quickly, which is why many startups use a fractional CFO until the role genuinely justifies a permanent seat.
To sketch your own numbers, our income tax calculator is a quick way to model a director's take-home before you commit to a salary.
Do you need both a CFO and an accountant?
Usually, yes, and they don't conflict. A fractional CFO does not replace your accountant. The CFO sets strategy and direction; the accountant produces the accurate records and compliant filings that the strategy is built on.
In a well-run setup, the accountant keeps the books clean and the CFO uses those books to forecast, advise and report. If you only had a CFO, you'd still need someone to file your accounts and run payroll. If you only had an accountant, you'd be making big bets without a forecast.
For many startups the smart sequence is: bookkeeper or accountant first, fractional CFO added when you start raising or scaling, full-time CFO only once the company is large enough to keep one fully occupied.
How do you decide? A simple checklist
Run through these. If you tick three or more in the second column, it's probably time to talk to a fractional CFO. If you're mostly in the first column, a strong accountant is likely all you need right now.
| You probably need an accountant (only) | You probably need a fractional CFO (too) |
|---|---|
| Pre-revenue or early, simple revenue | Raising a round in the next 6 to 12 months |
| Cash flow is predictable month to month | Cash flow is lumpy and hard to forecast |
| No institutional investors yet | Investors or a board expecting monthly packs |
| Few staff, no share scheme | Planning EMI options or SEIS/EIS structuring |
| Decisions are low-stakes financially | Big pricing, hiring or expansion calls ahead |
| You just need compliance done right | You need a model, a forecast and a plan |
If you're genuinely between the two, that's normal, and it's often the moment to get advice rather than guess.
Want help working out which you need?
At Zmartly we do both the accounting and the fractional CFO work, so you're not stitching two firms together. Book a free 20-minute call and we'll tell you honestly which one your startup needs right now. Learn more about our fractional CFO and US CFO services, or get in touch to talk it through.
FAQs
Can a fractional CFO replace my accountant?
No. They do different jobs. A fractional CFO focuses on strategy, forecasting and fundraising, while an accountant handles bookkeeping, statutory accounts, tax and payroll. Most growing startups need both, with the CFO building on the accurate records the accountant produces.
When is the right time to hire a fractional CFO?
When you're preparing to raise, scaling quickly, or finding that cash flow and big financial decisions have outgrown a simple spreadsheet. A common trigger for UK startups is the run-up to a Series A round. If your finances are still simple and predictable, a good accountant is usually enough for now.
Is a fractional CFO cheaper than a full-time CFO?
Yes. You pay for a day or two a week, or a set number of hours a month, rather than a full salary plus employer National Insurance, pension and benefits. For 2025/26 the employer National Insurance rate is 15% on earnings above the £5,000 secondary threshold, so a full-time senior hire carries significant on-costs that a fractional engagement avoids.
Do early-stage startups need a CFO at all?
Most very early startups don't. A solid accountant to keep you compliant, plus the founder owning a simple forecast, is often enough until you start raising money or scaling. Bringing in a fractional CFO too early means paying for strategic capacity you can't yet use.
Can the same firm provide both an accountant and a fractional CFO?
Yes, and it's often simpler. Using one firm for both means the strategy and the books stay joined up, with no handover gaps between two providers. At Zmartly we offer accounting and fractional CFO support together so the numbers behind your forecasts are the same numbers in your filed accounts.
