A cash-flow forecast estimates when money will actually enter and leave your business. A four-week version can help you see whether the next supplier bill arrives before the next customer payment. You can build it in a spreadsheet; the useful part is choosing realistic dates and checking them regularly.
The useful bits
- Use expected payment dates, not just invoice dates.
- Carry each week’s closing balance into the next week.
- Test a delayed-payment version as well as your expected plan.
Start with the money available today
Choose a start date and record the opening bank balance. If some of that money is already set aside for a bill or tax payment, show the planned outflow rather than treating the whole balance as spare spending money.
Create four weekly columns. Add rows for customer receipts, other money coming in, materials, regular bills and any other planned payments. Include owner withdrawals as cash leaving the business, but keep them separate from operating costs. Extend the forecast beyond four weeks if your jobs or payment terms run longer.
Put receipts in the week you expect to receive them
An invoice issued on Monday is not automatically cash available on Monday. Use the agreed due date, the customer’s payment history and any confirmed payment promise. Keep uncertain new work separate from agreed jobs so that a hoped-for booking does not quietly become a guaranteed receipt.
The British Business Bank’s forecasting guide makes the same timing distinction: forecast when payments arrive, not simply when sales are made. For card payments, also allow for the provider’s payout timing.
Work through four weeks
The calculation is opening cash plus money received minus money paid out. Carry the result forward. This fictional example ignores VAT and tax calculations and uses total cash movements solely to demonstrate the method.
| Cash movement | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Opening cash | £1,000 | £900 | £1,400 | £300 |
| Money received | £800 | £1,200 | £400 | £1,400 |
| Money paid out | £900 | £700 | £1,500 | £800 |
| Closing cash | £900 | £1,400 | £300 | £900 |
What the example reveals
The month ends with £900, but the lowest weekly closing balance is £300. That is the week to investigate. A positive month-end number does not show whether a large bill falls before a receipt within the same week; inspect the individual dates when the margin is tight.
Test one payment arriving late
Move the £1,200 week-two receipt into week four. Week two then closes at £200, and week three closes at minus £900. The original forecast looked workable, but this version identifies a cash gap before the late money arrives.
Use that information to review the payment promise, schedule optional spending or discuss supplier timing early. Changing a spreadsheet date does not change a contract: agree any changed payment arrangements with the other party.
Replace predictions with actuals each week
Keep a copy of the original forecast, then update it with actual receipts and payments. Note why a number changed: a postponed job, extra materials or a customer paying early. Add another week so the forecast always looks ahead.
Finish with one action attached to the nearest pinch point. That might be confirming a payment date or checking the cost of next week’s materials. A forecast earns its place when it changes a decision.
Sources and further reading
Sources checked 28 September 2026. Follow the official guidance for the current rules and how they apply to your business.
