How to Create a SaaS Budget: UK Step-by-Step Guide

This is a practical guide to building a 12-month operating budget for a UK SaaS company. No theory, no generalisations -- just the steps, the numbers, and the UK-specific details that founders tend to get wrong.

If you have never built a budget before, follow this from top to bottom. If you have a budget but it is not working, skip to the sections that are causing you problems.

Step 1: Revenue forecasting -- start from your MRR schedule

Do not start with an ARR target and divide by 12. That gives you a flat line that tells you nothing about when revenue actually lands.

Start with your MRR schedule. Pull your current monthly recurring revenue, broken down by customer. Then build forward:

• Existing customers. Apply your historical net revenue retention rate. If you are retaining 95% of MRR month-on-month after churn and expansion, use that. Do not assume retention will improve unless you have a specific initiative that justifies it.
• New business. Use your sales pipeline to estimate new logo MRR by month. Be conservative. If your average sales cycle is 60 days, a deal that enters the pipeline in January is not closing before March. Apply your historical win rate -- typically 20-30% for B2B SaaS.
• Expansion. If you have a usage-based or seat-based pricing model, estimate expansion revenue per cohort. Most SaaS companies see 2-5% monthly expansion from existing customers.
• Churn. Budget for it explicitly. If your gross churn rate is 1.5% per month, model that. Pretending churn will not happen is the fastest way to miss your revenue target.

The output should be a month-by-month MRR forecast that you can convert to recognised revenue. If you bill annually upfront, remember that cash collected is not the same as recognised revenue -- you will recognise it monthly over the contract term under FRS 102 Section 23.

Step 2: Staff costs -- the UK-specific numbers

Staff costs are typically 60-75% of total operating costs for a SaaS company. Getting them wrong makes the entire budget unreliable.

For each employee, budget for the fully loaded cost:

• Base salary. The gross annual salary.
• Employer’s National Insurance. Currently 15% on earnings above the secondary threshold (£5,000 per year from April 2025). For a £60,000 salary, employer’s NI is approximately £8,250 per year.
• Auto-enrolment pension. The minimum employer contribution is 3% of qualifying earnings. For a £60,000 salary, that is £1,800 per year. Many SaaS companies offer 5% to remain competitive with larger firms.
• Benefits. Private medical insurance (typically £500-£1,500 per employee per year), death in service cover, cycle-to-work schemes, and any other benefits you offer.

A £60,000 base salary costs the company approximately £71,850 per year once you add employer’s NI and 3% pension. At 5% pension, that rises to £73,050.

For new hires, include recruitment costs. Agency fees run 15-20% of first-year salary. If you are using a recruiter for a £70,000 role, budget £10,500 to £14,000 as a one-off cost in the month you expect the hire to start. Internal recruitment (job boards, LinkedIn recruiter seats) typically costs £3,000 to £5,000 per hire.

Build a headcount plan: list every existing employee and every planned hire, with their start month, salary, and department. This becomes the backbone of your cost budget.

Step 3: Software and technology costs

SaaS companies spend more on software than most founders realise. Audit your current subscriptions and budget for each one:

• Cloud infrastructure. AWS, GCP, or Azure. If you are growing, your infrastructure costs grow with you. Budget for 10-20% growth in hosting costs if you expect customer growth. Typical range: £2,000-£15,000/month depending on scale.
• Development tools. GitHub (£15/user/month), CI/CD pipelines, monitoring tools (Datadog, Sentry), project management (Linear, Jira). Budget £100-£200 per developer per month for tooling.
• Sales and marketing. CRM (HubSpot, Salesforce), email tools, analytics, SEO tools, ad platforms. These add up fast. A full sales and marketing stack can easily reach £2,000-£5,000/month for a 20-person company.
• Operations. Accounting software (Xero at £50-£75/month), payroll (£5-£10 per employee per month), HR platforms, communication tools (Slack, Zoom).
• AI tools. Budget £20-£50 per employee per month for AI assistants and productivity tools. This is a new line item that did not exist two years ago but is now a real cost.

The key discipline is to review subscriptions quarterly. SaaS companies are particularly prone to software bloat -- you are, after all, selling the same kind of product you are buying.

Step 4: Office and infrastructure

Remote-first companies still have costs:

• Co-working memberships. If you offer team members access to co-working spaces, budget £200-£400 per person per month.
• Home office equipment. Budget £500-£1,000 per new hire for a monitor, keyboard, chair, and desk setup.
• Team meetups. Remote teams need regular in-person time. Budget for quarterly meetups: venue hire, travel, accommodation. Typically £500-£1,000 per person per meetup.

If you have an office, add rent, business rates, service charges, utilities, and insurance. London office space runs £500-£800 per desk per month. Outside London, £200-£400.

Step 5: Marketing spend -- the benchmarks

Marketing spend for B2B SaaS typically falls between 20-40% of revenue, depending on stage:

• Pre-product-market-fit (under £500K ARR). Marketing spend is often ad hoc. Budget what you can afford, but expect to spend 30-50% of revenue on customer acquisition.
• Growth stage (£500K-£5M ARR). Target 25-35% of revenue on sales and marketing combined. This includes salaries for sales and marketing staff.
• Scale stage (£5M+ ARR). Marketing efficiency should improve. Target 20-30% of revenue.

Break marketing spend into categories: content and SEO, paid acquisition (Google Ads, LinkedIn), events and conferences, PR, and brand. Each should have a monthly budget with a clear expected return.

Step 6: Contingency -- why you need 10-15% buffer

Every budget should include a contingency line. Things will go wrong: a key customer will churn unexpectedly, a hire will take longer than planned, a supplier will increase prices.

Budget 10-15% of total operating costs as contingency. Do not allocate it to a specific category. It sits as a single line item that absorbs the unexpected.

If you reach the end of the year without using it, that money drops straight to your bottom line. If you use half of it, you still came in close to budget. Without it, every unexpected cost puts you over budget and makes the entire exercise feel pointless.

Step 7: Tax planning

Three tax areas that affect your budget directly:

Corporation tax. The main rate is 25% for companies with profits over £250,000. The small profits rate is 19% for profits under £50,000. Marginal relief applies between £50,000 and £250,000. Budget for your expected tax liability and remember: the payment is due nine months and one day after your accounting period ends.

R&D tax credits. If you are developing software, you almost certainly qualify. Under the merged R&D scheme (effective from April 2024), the relief is an above-the-line credit of 20% of qualifying expenditure. For loss-making SMEs, the enhanced R&D intensive scheme provides a higher credit rate of 27%. Qualifying costs include staff costs (salaries, NI, pension contributions) for employees working on R&D, plus subcontractor costs (at 65%), cloud computing, and consumable items. This can materially reduce your effective tax rate. Budget for the credit as a reduction to your tax line, and file your R&D claim with your corporation tax return.

VAT cash flow. If you bill annually upfront, you collect 20% VAT on the full invoice value. That cash sits in your bank account until the quarterly VAT return is due (one month and seven days after the quarter end, per HMRC rules). This creates a temporary cash float that can be significant. For a £100K annual invoice, you are holding £20K of VAT for up to three months. Budget for the quarterly VAT payment and do not treat that cash as yours.

Step 8: Monthly budget review process

The budget is only useful if you review it monthly. Here is the process:

1. Close your management accounts. Reconcile bank, post accruals, and produce a monthly P&L. This should happen within 10 working days of month-end.
2. Run the variance report. Compare actual costs against budget, line by line. Flag anything over 10% variance.
3. Investigate material variances. A variance is only useful if you understand the cause. "Marketing was £3K over budget because we brought forward the conference sponsorship from Q3 to Q2" is useful. "Marketing was over budget" is not.
4. Reforecast quarterly. Take actuals for months completed, keep the budget for remaining months, and adjust for known changes. This gives you a realistic full-year outlook.
5. Report to the board. If you have a board, the variance report and reforecast should be a standing item in every board pack.

The discipline of monthly reviews creates accountability. It also gives you early warning. If you are trending 15% over budget in Q1, you have three quarters to correct it. If you do not look until year-end, it is too late.

The bottom line

A 12-month budget is not optional for a SaaS company that wants to grow sustainably. It takes two to three weeks to build properly, and an hour per month to maintain. The return -- in terms of financial control, hiring discipline, and investor confidence -- is substantial.

If you need help building a budget that works, explore our financial planning service or book a call to discuss how a fractional CFO can support your budgeting process.