Businesses do not usually fail because the annual budget was wrong. They fail because nobody knew, in week three, that week eleven was going to be short. Cash flow monitoring is the discipline of knowing that — far enough in advance that the response is a decision rather than an emergency — and it is a different exercise from the annual forecast that sits in the business plan.
The thirteen-week rolling forecast
The standard tool is a 13-week direct cash flow forecast: week by week, cash in and cash out, opening and closing balance, rolled forward every week so the horizon stays constant. Thirteen weeks is not arbitrary — it is long enough to see a quarter's tax payments and a seasonal trough coming, short enough that the individual lines are real receipts and payments rather than estimates.
"Direct" means built from actual expected transactions — this customer, that invoice, that payroll date — rather than derived from profit by adjusting for working capital movements. The indirect method has its place in longer-term modelling, but it cannot tell you which Friday the account goes below zero, and that is the question.
The receipts line is where the forecast lives or dies. Forecasting customer payments on invoice terms rather than on each customer's actual behaviour produces a document that is optimistic every single week. If a customer has paid at 62 days for two years, they will pay at 62 days next month, whatever the invoice says.
The variance review is the part that creates value
A forecast nobody checks against reality degrades within a month. The weekly routine that works takes half an hour: compare last week's forecast to what actually happened, explain every material difference, and adjust the assumptions that caused it. Over a quarter this converts a spreadsheet into something with a known accuracy — and a forecast whose error you can quantify is a forecast you can make decisions on.
The variance analysis also functions as an early warning system in its own right. A receipts line that under-delivers three weeks running is not a forecasting problem; it is a collections problem, or a customer problem, and it is visible here before it is visible anywhere else.
What to watch alongside the balance
Four measures turn the forecast into a working capital conversation:
- Debtor days — how long customers actually take to pay, tracked as a trend rather than a snapshot. A week of movement on £2m of annual credit sales is roughly £38,000 of cash, assuming sales and receivables are measured on the same basis, VAT included or excluded consistently. The same calculation does not carry across to stock or creditor days, which are measured against cost of sales and purchases;
- Creditor days — the mirror, with the caveat that stretching suppliers is borrowing at a high implicit rate and is visible to them;
- Stock turn, where the business holds inventory, since slow stock is cash sitting on a shelf;
- Headroom — the gap between the forecast low point and the facility limit, which is the number that should be reported to the board rather than the closing balance.
The cash conversion cycle — debtor days plus stock days less creditor days — sums them into the number of days the business must fund itself. Businesses that grow quickly fail here more often than businesses that shrink: growth consumes working capital, and a profitable company expanding at 40% a year can run out of cash while every management report looks excellent.
Scenarios, not a single line
A single forecast is a prediction, and predictions are wrong. Three cases make it useful: a base case on current expectations, a downside that assumes a genuinely bad combination — the largest customer pays 30 days later, sales fall 15%, a receipt slips a quarter — and an upside. The point of the downside is not pessimism; it is to identify the week the business would breach its facility, so that the conversation with the bank happens while it is hypothetical.
Where covenants exist, test them in every scenario. A covenant breach is frequently a more immediate threat than running out of cash, because it hands control of the timetable to the lender.
The routine that makes it stick
Weekly: update the forecast, review the variance, review the aged debt over 60 days with a named owner per account. Monthly: reconcile the cash forecast to the management accounts, refresh the assumptions, report headroom and covenant position to the board. Quarterly: re-run the downside case and confirm the facility is still adequate for the next twelve months.
What makes it work is ownership. The forecast belongs to the finance lead but the receipts assumptions belong to whoever owns the customer relationships, and the two have to talk weekly. Where that conversation does not happen, the forecast becomes a finance document about sales, which is to say fiction.
Acumon builds and runs this alongside management accounts and financial modelling, with cloud accounting providing the underlying data in real time — and the collections side covered in our guides to credit control and trade debtors. If your business currently learns about a cash problem from the bank balance, thirteen weeks of visibility is the cheapest control you can add.