Pillar Guide · Updated July 2026
UK Cash Flow Forecasting for Small Business: A Complete Guide for 2026/27
Running out of cash, not lack of profit, is one of the most common reasons small businesses fail. This guide explains how to build a practical cash flow forecast, why VAT and tax payment timing matters so much, and how to spot and manage a cash gap before it becomes a crisis.
What a Cash Flow Forecast Is
A cash flow forecast is a projection of the money you expect to receive and pay out of your business over a future period, usually broken down month by month, showing an opening cash balance, forecast cash in, forecast cash out, and a resulting closing balance for each period. Its main purpose is to give you early warning of periods where the business might run short of cash, well before that shortfall actually arrives.
Cash Flow vs Profit
Profit and cash flow are different measures. Profit is income earned less expenses incurred over a period, regardless of exactly when cash actually moves, while cash flow tracks the real timing of money in and out of your bank account. A business can be genuinely profitable on paper while still running out of cash — for example, if customers take a long time to pay invoices, or a large VAT or tax bill falls due before enough cash has actually come in from sales.
Building a Simple Forecast
A practical starting point is a rolling 12-month forecast, updated monthly, with a more detailed weekly or fortnightly view for the next one to three months where near-term accuracy matters most. List expected cash inflows (customer payments, based on realistic payment timing rather than invoice dates) and expected cash outflows (supplier payments, payroll, rent, loan repayments, and tax and VAT payments) for each period, then calculate the running closing balance to see where the business's cash position is heading.
VAT Payment Timing
If your business is VAT registered, VAT collected on sales (net of VAT reclaimed on purchases) must be paid over to HMRC at your normal VAT return frequency, commonly quarterly. It is important to build the actual VAT payment date and amount into your forecast as a specific cash outflow, rather than treating VAT collected from customers as available cash the business is free to spend, since that VAT ultimately belongs to HMRC and not the business.
Corporation Tax and Self Assessment Timing
For a limited company, Corporation Tax is normally due nine months and one day after the end of the accounting period (for smaller companies not required to pay by quarterly instalments), while sole traders and partners pay tax through Self Assessment, including any payments on account due in January and July. Build an estimate of the expected tax liability, based on projected taxable profits, into your forecast as a cash outflow in the correct month, so the payment does not come as a surprise.
Common Mistakes
One of the most frequent cash flow forecasting mistakes is treating VAT collected or funds set aside for tax as if they were ordinary available cash, only to discover a shortfall when the VAT return or tax bill actually falls due. Keeping VAT and tax money in a separate savings account, or at least clearly ring-fencing it within your forecast, helps avoid inadvertently spending money that is not really the business's to spend.
Managing a Forecast Shortfall
Spotting a future cash shortfall in your forecast gives you time to act before it becomes urgent. Options can include chasing overdue customer invoices sooner, agreeing extended payment terms with suppliers, arranging a business overdraft or other short-term finance facility, or delaying discretionary spending until the position improves. All of these options are far easier to arrange calmly in advance than in the middle of an actual cash crisis, which is the core value of forecasting regularly.