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The 13-week cash-flow
forecast, explained.
Ask a lender, an investor or a turnaround adviser for one number and they will ask you for thirteen weeks of cash. The rolling 13-week forecast is the single most useful planning tool a company owner can keep — here is what it is, and how to build one.
Profit is an opinion; cash is a fact. A company fails when it runs out of cash, not when it runs out of profit — and the 13-week forecast is the tool that shows the cash coming.
A profit-and-loss account tells you whether the business model works over time. It will not tell you whether you can make Friday's payroll. For that you need a view of actual money moving through the bank account, week by week — which is exactly what a 13-week cash-flow forecast gives you.
It is the first artefact a lender's credit team, an equity investor or a restructuring adviser will ask to see, because it reveals the one thing that matters in the short term: are you going to have enough cash in the bank, every single week, to meet what falls due?
Why cash and profit are not the same
The difference comes down to timing. Your accounts are prepared on the accruals basis; your bank account works on the cash basis:
- Accruals (your P&L). Income is recognised when it is earned and costs when they are incurred — the day you raise an invoice, the profit appears, even though no money has moved.
- Cash (your forecast). A receipt only counts on the day the money clears; a payment only counts on the day it leaves. This is the world the 13-week forecast models.
How to build one
Five steps, in one spreadsheet.
- Set up the grid and the opening balance. Thirteen weeks across the top, line items down the side. In week one, enter today's actual cleared bank balance. Group the rows: opening balance, receipts, payments, and a bold closing-balance row at the bottom.
- Time your receipts by when cash actually clears. Put each expected customer payment in the week you realistically expect it to hit the bank — based on how that customer really pays, not the invoice date. When in doubt, forecast it late.
- List every payment, including the lumpy ones. Payroll and PAYE/NIC on their run dates; supplier runs; and the big periodic outflows in the exact week they fall — rent quarters, VAT, corporation tax, insurance renewals, loan repayments, capital spend. The lumpy items are what catch people out.
- Calculate the closing balance and read the low points. Opening + receipts − payments = closing, carried into next week. Then read the closing-balance row across all 13 weeks: the lowest points are your pinch weeks.
- Roll it forward every week and compare to actuals. Replace each finished week's forecast with what actually happened, drop it off the front, add a new week 13. Adjust assumptions where forecast and actual diverged. This weekly rhythm is what makes the model trustworthy.
What a good 13-week model tells you
- Your pinch weeks. The specific weeks where the closing balance dips lowest — and by how much — so you can act weeks ahead rather than the day before.
- Your true runway. How many weeks of cash you have if nothing changes, which is the number every investor and lender wants.
- The size and shape of any gap. Whether a shortfall is a one-off (suited to a short lump-sum bridge) or a recurring pattern (suited to a facility you draw and repay).
- Which lever to pull. Chase a receipt, defer a payment, cut a cost, or arrange finance — the model lets you test each one before committing.
13-week forecasting: common questions
Why 13 weeks specifically?
Thirteen weeks is one calendar quarter. It is long enough to see the major cash events coming — a VAT quarter, a rent quarter, payroll runs, a large customer receipt — but short enough that you can forecast each week with real confidence rather than guesswork. It has become the standard horizon lenders and turnaround professionals use because it balances visibility against accuracy: beyond a quarter, weekly precision decays; inside it, you can plan concrete actions.
How is a 13-week forecast different from a normal budget or P&L?
A budget or profit-and-loss statement is built on the accruals basis: it recognises income when it is earned and costs when they are incurred, regardless of when cash actually moves. A 13-week cash-flow forecast is the opposite — it is built on the direct, cash basis: it only counts money on the days it actually lands in or leaves the bank account. That is why a profitable company can still run out of cash, and why the 13-week model exists: it tracks liquidity, not profit.
What are the main line items in a 13-week model?
Start with the opening bank balance. Then list receipts (customer payments, timed by when you realistically expect them to clear — not the invoice date), and payments (payroll and PAYE/NIC, supplier payments, rent, VAT, corporation tax, loan repayments, VAT-inclusive costs, and any capital spend). Each week: opening balance + receipts − payments = closing balance, which becomes next week's opening balance. The closing-balance row is the one everyone reads first — it shows the low points.
What does "rolling" mean?
A rolling forecast is updated every week: you drop the week that has just finished, add a new week 13 at the far end, and — crucially — replace your forecast figures for the past week with what actually happened. Comparing forecast against actual each week is where the model earns its keep: consistent variances tell you your assumptions are wrong (customers pay slower than you assumed, say), and you correct them. A forecast built once and never revisited is close to useless.
Do I need special software to build one?
No. Most 13-week forecasts live in a single spreadsheet: weeks across the top, line items down the side, one clearly labelled row for the closing bank balance. Accounting packages and dedicated cash-flow tools can automate the feeds, which helps once the model is embedded, but the discipline matters far more than the tool. A well-maintained spreadsheet beats an automated model nobody reviews.
Related reading
When the forecast shows a gap, read debt or equity? to weigh how to fund it, and the product-side cash-flow gap guide and working capital finance on the Learn hub. Keeping the numbers current is also part of a director's statutory duties. All the briefings are on the Insights hub.
See the pinch coming. Act early.
When the forecast shows a short gap, same-day company finance can bridge it.