Fractional CFO for SaaS & AI Founders in the UK: Services & Pricing
Investor-ready financials, reliable forecasts, and a CFO who responds quickly. Fixed monthly retainer of £2,000-£5,000/month nationwide. No day rates. No surprises.
Do you recognise this?
Most SaaS founders between £500K and £5M ARR do not have anyone looking at their numbers with a critical eye. If two or more of the following apply, your data is not investor-ready.
What a SaaS CFO does
A SaaS CFO provides the financial leadership that subscription businesses need but most accountants cannot deliver. Your accountant looks backwards at what happened; a SaaS CFO looks forward at what should happen next.
Unlike a traditional CFO who focuses on gross margin and EBITDA, a SaaS specialist tracks the metrics that actually drive subscription business value: MRR movements, cohort-level retention, expansion revenue, and unit economics by acquisition channel. These metrics do not appear in standard financial statements, yet they are the first thing investors examine. A fractional CFO delivers the same SaaS expertise without the full-time overhead.
SaaS metrics tracked every month
These are the metrics we build, track, and report for every SaaS client. Each tells investors something specific about your business health and growth trajectory.
Monthly Recurring Revenue (MRR)
Track new, expansion, contraction, and churned MRR each month. This is the heartbeat of your subscription business and the first number every investor asks for.
Annual Recurring Revenue (ARR)
MRR multiplied by 12 gives your run-rate ARR. This is the headline valuation driver for SaaS companies at every stage from Seed to Series B.
Net Revenue Retention (NRR)
Measures how much revenue you retain and expand from existing customers. Top-quartile SaaS companies achieve 110-130% NRR, meaning they grow without acquiring a single new customer.
Gross Revenue Retention (GRR)
Revenue retained before expansion. Anything below 85% signals a product or service problem that no amount of new sales can fix.
Customer Acquisition Cost (CAC)
Total sales and marketing spend divided by new customers acquired. Track by channel to understand which acquisition paths are efficient and which are burning cash.
LTV:CAC Ratio
Customer lifetime value divided by acquisition cost. Investors expect at least 3:1. Below that, you are spending more to acquire customers than they are worth.
CAC Payback Period
How many months until a new customer pays back their acquisition cost. Under 12 months is strong. Over 18 months means you need more capital to grow.
Burn Multiple
Net burn divided by net new ARR. A burn multiple under 2x means you are growing efficiently. Above 3x means you are buying growth at an unsustainable rate.
Pricing - £2,000-£5,000/month full-service nationwide
Every engagement covers the same full-service scope. The retainer scales with business complexity, not feature access. A Pre-Seed founder paying £2,000 a month gets the same scope of work as a Series A+ company paying £5,000.
| Stage | Monthly retainer | Typical focus |
|---|---|---|
| Pre-Seed / Seed | £2,000 - £3,000/month | Cash flow survival, initial financial model, first board pack, SEIS/EIS compliance |
| Seed / Pre-Series A | £2,500 - £4,000/month | Fundraising model, investor reporting, monthly management accounts, unit economics tracking |
| Series A+ | £3,500 - £5,000/month | Finance team oversight, complex modelling, M&A support, multi-entity structure |
See how much a fractional CFO costs in the UK for the full pricing breakdown and what is included in every engagement.
Everything your SaaS finance function needs
From messy books to investor-ready financials - hands-on execution, not advisory-only.
Cash flow forecasting
Most founders calculate runway wrong because they use accounting losses rather than actual cash burn. We build proper cash flow forecasts, including scenario analysis under conservative, base and best-case assumptions, so you know precisely when you run out of cash and what levers you can pull. See our cash flow forecasting guide for UK SaaS startups for the methodology.
Fundraising & financial models
From angel rounds to Series A to venture debt - we build the financial model, prepare the data room, handle covenant reporting, and make sure the numbers you quote in investor meetings are the numbers that actually exist in your accounts. Mismatched figures between pitch decks and accounting records are among the most common reasons UK SaaS fundraises stall at due diligence. Read our guides on building a seed financial model and the Series A model.
Monthly reports & board packs
Nobody reads a 15-page PDF in full. We send you the three things that matter at 8am on Monday, with the full detail ready when an investor asks a question at 9pm on a Tuesday. Every monthly board pack includes MRR waterfall, ARR bridge, cohort analysis, CAC by channel, NRR, gross margin, runway under base / upside / downside scenarios.
Financial clean-up & restructure
Your revenue looks erratic because nobody spreads annual contracts across 12 months. We fix how revenue is recorded under FRS 102 / IFRS 15, rebuild the chart of accounts by department, reconcile Xero with your subscription data in Stripe and HubSpot, and produce financials that investors can interrogate without finding inconsistencies.
Profitability & margin improvement
Your gross margin is likely wrong because engineering and customer success costs are classified as operating expenses rather than cost of sales. We correct the COGS allocation so your margins reflect commercial reality - one of the most frequently flagged issues in SaaS due diligence, where investors always scrutinise gross margin line items in detail.
Exit preparation
If a buyer approached tomorrow, could you hand them clean financials within days? Fixing disorganised historical data typically takes two to three months. We get you ready before that conversation becomes urgent - not after. See the full SaaS unit economics framework we use to prepare clients for investor scrutiny, and our UK SaaS valuation multiples guide.
What investors will find - and what to fix first
Investors now use AI-assisted tools during due diligence. Every inconsistency in your data is flagged within minutes. These are the four problems they find most often in UK SaaS companies.
Revenue that does not add up
The recurring revenue figure you quote in meetings does not match the revenue in your accounts. Renewal contracts booked in the wrong period, annual subscriptions recognised as a lump sum instead of spread across 12 months. Overstated MRR and incorrect revenue recognition under FRS 102 are the single most common issues affecting UK SaaS valuations.
Inflated gross margin
Your margin reads 90% because engineering and customer success costs are sitting in operating expenses rather than cost of sales. Investors always scrutinise this, and a material error here destroys trust immediately - not because they object to the actual cost structure, but because it signals weak financial controls.
Customer concentration risk
Your top three customers account for more than 50% of revenue. That is a risk discount in any valuation model. You need the underlying data to demonstrate it is manageable - customer cohort analysis, renewal rates, contract lengths - not just a verbal assurance.
No retention or efficiency metrics
No way to show net revenue retention, CAC payback, or how your customer cohorts behave over time. If the underlying revenue data is wrong, none of these numbers can be trusted - and most investors will stop the process rather than attempt to rebuild the metrics themselves.
How ScaleWithCFO is different
Most fractional CFOs give you advice. We give you advice - and do the work.
Fixed retainer
One monthly fee covers everything. No day rates, no surprise invoices, no scope disputes mid-engagement. £2,000-£5,000/month full-service nationwide.
SaaS / AI specialist
Deep working knowledge of MRR, ARR bridges, unit economics, net revenue retention, and investor reporting language. We do not need to be briefed on what churn means.
Hands-on execution
We restructure your chart of accounts, fix your COGS allocation, and reconcile your Xero data to Stripe. We do not produce a recommendation document and hand it back to you.
Rapid response
Unlimited email support. 90% of messages replied to within 2 hours, with a 24-hour guarantee. You will not be waiting days for answers to urgent questions.
What founders say
Read all reviews on Trustpilot.
"Constantin knows his stuff and it was a really professional experience working with him. We will keep engaging Constantin to support us with our financial strategy. Only positive things to say about his services."
"Our CFO Constantin is always there for us, with clear reporting, useful insights (that we can't see as we are too close), and quick replies to our questions. A fractional CFO makes so much sense. A lifetime of experience at a fraction of the cost."
Hey, I'm Constantin
I am CIMA qualified and the founder of ScaleWithCFO. I work directly with SaaS, AI and technology founders across London and the UK who need a senior finance partner without making a full-time hire.
Whether you are preparing to raise, cleaning up historical data, or planning an exit - I handle it hands-on so you can focus on building the business.
From first call to fully operational in 90 days
Every engagement follows the same proven structure. By day 90, your financials are clean, your forecast is built, and your first board pack is delivered.
Clean up & restructure your financials
- Rebuild your chart of accounts by department (Sales, Marketing, Development, G&A)
- Fix how revenue is recorded - spread annual contracts across 12 months under FRS 102
- Split costs correctly between cost of sales and operating expenses
- Reconcile Xero with subscription data from Stripe, HubSpot and your CRM
- Audit gross profit margin and correct COGS allocation
- Review historical data so investors see a clean, consistent trail
Cash flow forecast & financial planning
- Build an operational cash flow forecast with scenario analysis
- Calculate runway under conservative, base and best-case scenarios
- Review your sales pipeline and model expected revenue by cohort
- Set budgets with team leaders for the next 12 months
- Build unit economics - acquisition cost, lifetime value, payback period
- Identify cash leaks and opportunities to extend runway
First board pack delivered
- Monthly report with KPIs, management commentary and recommendations
- Revenue waterfall: new customers, expansions, downgrades, churn, net new
- Retention metrics: net revenue retained, customer renewal rates
- Efficiency metrics: CAC payback, burn vs growth, LTV/CAC ratio
- Customer concentration and cohort analysis
- Strategic planning aligned to your fundraising or exit timeline
Frequently asked questions
A SaaS CFO understands subscription mechanics natively - MRR / ARR bridges, deferred revenue under FRS 102, net revenue retention, cohort analysis, CAC payback, burn multiple. A generalist CFO can learn these but spends the first few months on the learning curve while you pay for the time. A SaaS specialist applies the framework immediately.
Every engagement covers the same full-service scope - cash flow forecasting, financial model, monthly management accounts and board pack, SaaS / AI KPI dashboard, fundraising and investor relations support, M&A and exit prep when relevant, and ad-hoc strategic advice. The retainer scales with business complexity, not feature access. Pre-Seed/Seed £2,000-£3,000, Seed/Pre-Series A £2,500-£4,000, Series A+ £3,500-£5,000.
Both. The model is the same: subscription or usage-based revenue, recurring customer base, and the same financial dynamics. AI startups have specific cost considerations (compute / inference costs, model training spend, ERIS R&D eligibility) that we factor into the model.
Typically within 1-2 weeks of the discovery call and NDA. The first 2 weeks are a diagnostic phase reviewing your current state; meaningful financial output usually arrives in weeks 3-4. By day 90 your financials are clean, your forecast is built and your first board pack is delivered.
Yes. We build the financial model, prepare the data room, present investor-ready financials, and support due diligence. To date ScaleWithCFO has helped clients raise £21.3M. See our guides on building a Series A model and avoiding common financial model mistakes that derail fundraising.
All engagements run on month-to-month terms with 30-day notice for flexibility. In practice, many founders stay 2-3+ years - through clean-up, fundraising, and the early scale-up phase. Some end after a specific event (fundraise, exit); others continue until the company is large enough to justify a full-time CFO.
Ready to bring CFO-level thinking to your SaaS business?
Free 15-minute call. No obligation, no day rates.