A healthy sales month can still leave a business short of cash. You may have issued invoices, won new work and shown a profit on paper, yet still be wondering whether there is enough in the bank for wages, VAT or a key supplier payment. This cash flow forecasting guide explains how to see those pressures before they become urgent, and make decisions with greater confidence.
For small businesses, contractors and growing companies, a forecast does not need to be complicated to be useful. It needs to be realistic, kept up to date and clear enough to help you act at the right time.
What a cash flow forecast tells you
A cash flow forecast is a forward-looking estimate of money entering and leaving your bank account over a set period. It normally starts with your opening bank balance, adds expected receipts, deducts planned payments and shows the expected closing balance for each week or month.
It is different from a profit and loss report. Profit records income and costs when they are earned or incurred. Cash flow follows the date money is actually received or paid. If you invoice a customer in March but they pay in May, the sale may improve March profit, but it does not help you meet April payroll.
That distinction matters when you are deciding whether to recruit, buy equipment, take on premises, pay yourself a dividend or agree longer payment terms with a customer. A forecast turns those decisions into a practical question: can the business afford the timing?
Choose a forecast period that suits your business
The right level of detail depends on how quickly cash moves through your business. A start-up, construction business, hospitality venue or company with tight margins may benefit from a rolling 13-week forecast, updated weekly. This gives early warning of near-term pressure and is particularly helpful where payroll and supplier costs fall on fixed dates.
For a more established service business with reliable monthly income, a 12-month monthly forecast can support broader planning. It can show the effect of quieter trading periods, annual insurance renewals, corporation tax, VAT and planned investment.
Many businesses need both. Use a weekly view to manage the immediate bank position, then a monthly view to plan ahead. The trade-off is time: a highly detailed forecast is only worthwhile if it is reviewed often enough to remain accurate.
Start with the bank balance, not optimism
Begin with the cleared balance across every business bank account on the day you prepare the forecast. If money is held in a savings account but is available for day-to-day use, include it separately so the position is transparent. Do not treat an overdraft facility as cash you already have. It is a source of funding that may carry conditions and cost.
Next, list expected receipts by the date they are likely to arrive, rather than the date you hope they will arrive. Use your customer payment history. A client on 30-day terms who usually pays after 45 days should be forecast at 45 days until their behaviour changes.
For sales not yet invoiced, be cautious. Include confirmed orders and recurring work where there is a sound basis for doing so. Potential projects, verbal promises and opportunities still at quotation stage are better kept out of the main forecast, or shown separately as an upside scenario.
Record every material outgoing
The most useful forecasts capture routine costs as well as the less frequent payments that can catch a business out. Regular costs may include wages, pension contributions, rent, software, loan repayments, insurance, fuel, stock, subcontractors and supplier invoices.
Tax payments deserve their own lines. Depending on your circumstances, these may include VAT, PAYE and National Insurance, corporation tax, self-assessment liabilities and payments on account. They are not unexpected costs, but they are often substantial and easy to overlook when cash is being used elsewhere.
Also allow for annual renewals, equipment repairs, professional fees, holiday pay and deposits. If your directors take drawings or dividends, record these too. A forecast should show the full picture, not just operating expenditure.
Include the timing, not simply the total
A common mistake is to place a monthly cost evenly across the month when it is actually paid on one date. That can hide a shortfall. If payroll leaves the account on the 28th and a major customer pays on the 30th, the business may need funding for two days even if the month ends with a positive balance.
This is why weekly forecasting can be valuable. It highlights timing gaps that a monthly forecast may smooth over.
Build a simple working forecast
A spreadsheet is often sufficient at first, provided the information comes from reliable records. Cloud accounting software can also help by bringing bank transactions, invoices and bills into one place, but the forecast still needs judgement. Software cannot know that a customer is disputing an invoice or that a supplier has agreed to defer payment unless you update the assumptions.
A straightforward layout is:
| Period | Opening balance | Cash in | Cash out | Closing balance | |—|—:|—:|—:|—:| | Week 1 | £12,000 | £4,500 | £6,200 | £10,300 | | Week 2 | £10,300 | £2,000 | £8,750 | £3,550 |
The closing balance from one period becomes the opening balance for the next. Behind the totals, keep a schedule of individual invoices and payments. This makes it far easier to check assumptions and identify which amounts need chasing or rescheduling.
Test the forecast before relying on it
A forecast is an informed estimate, not a guarantee. The aim is not to predict every pound perfectly; it is to understand what could change the outcome and prepare accordingly.
Consider three views of the same period: expected, cautious and positive. In the cautious version, delay one or two large customer receipts, reduce projected sales where work is not confirmed and allow for an unexpected cost. In the positive version, include realistic opportunities that may convert or earlier payment from a reliable customer.
This approach prevents a single optimistic number from driving important decisions. It also helps you see how much cash buffer the business needs. The appropriate buffer varies. A business with predictable subscriptions and low fixed costs may need less than one dependent on a small number of large invoices or seasonal sales.
Use the forecast to take action early
The value of forecasting comes from what you do with the information. If a shortfall is showing six weeks ahead, you have options that may not be available three days before payroll.
You might chase overdue invoices sooner, ask for deposits on new work, phase a planned purchase, negotiate supplier terms or review whether drawings can wait. If external funding is needed, approaching a lender with a clear forecast and a plan is generally stronger than seeking finance in a crisis.
Equally, a forecast may show that cash is building up. That can support measured decisions about investment, debt repayment, recruitment or tax-efficient extraction. A positive balance does not automatically mean surplus cash, though. Check what has been set aside for VAT, tax and known commitments before spending it.
Review it as part of your routine
Set a regular time each week or month to compare forecast figures with what actually happened. Update bank balances, mark invoices as paid, move delayed receipts to more realistic dates and add newly agreed costs. This is where the forecast improves over time.
Look for patterns rather than treating every variance as a failure. Are particular customers consistently late? Is stock tying up more cash than expected? Are tax payments creating recurring pressure? These insights can lead to better credit control, pricing, payment terms and purchasing decisions.
Management accounts and up-to-date bookkeeping make this process much easier because they provide a dependable starting point. Where the figures are incomplete or several months behind, forecasting becomes guesswork. Bringing records up to date is often the first practical step.
When to ask for support
A business owner should not have to carry every financial decision alone. Professional support can be especially useful when cash is tight, the business is growing quickly, funding is being considered or tax commitments are difficult to plan around. An accountant can help create a workable model, challenge assumptions and explain what the figures mean in plain English.
At Coombs Chartered Accountants, we see cash flow forecasting as a tool for calmer, better-timed decisions, not another administrative task. A forecast will never remove every uncertainty, but keeping it current gives you something far more useful than a hopeful bank balance: time to choose your next move.
