How to build a 13-week cash-flow stress test

Why 13 weeks is useful

A monthly profit forecast can look healthy while the bank account still runs short between a supplier payment and a late customer receipt. A 13-week cash-flow forecast keeps the planning horizon short enough to use real dates, while still showing roughly one quarter of upcoming decisions.

The purpose is not to predict every pound or dollar perfectly. It is to reveal the week in which available cash becomes tight, identify which assumptions cause the pressure and leave time to change the plan before payment is due.

Start with cash you can actually use

Enter the cleared bank balance at the start of week one, then subtract any amount that is ring-fenced for payroll, tax, customer deposits or another specific obligation. Do not count an unused overdraft, unpaid invoice or expected investment as cash unless the funding is already available under terms you understand.

Label restricted amounts separately. A forecast is more useful when it shows that £20,000 is in the bank but only £11,000 is available for normal operations than when it treats the whole balance as spendable.

Place receipts in the week they should clear

List customer receipts invoice by invoice when they are material. Use the realistic payment date, not the invoice date or contractual due date, and separate confirmed receipts from hopeful sales. Smaller recurring receipts can be grouped if the underlying pattern is stable.

For a worked example, suppose a business starts with £18,000 of usable cash and expects £9,000 from a large customer in week four. The base case may stay positive. Moving that single receipt to week seven can expose a shortfall in week five even though total quarterly sales have not changed.

• Confirmed: invoice issued and payment timing is credible.
• Probable: expected sale or collection with a defensible date.
• Possible: pipeline value kept outside the base case and tested separately.

Map payments to their real dates

Add payroll, rent, supplier invoices, loan repayments, tax, software renewals and owner drawings in the week the money should leave the bank. Split quarterly or annual bills from normal weekly spending so a large scheduled payment does not disappear inside an average.

Separate committed payments from discretionary ones. That distinction turns a warning into an action list: committed payments need funding or negotiation, while discretionary spending may be delayed without pretending the underlying obligation has vanished.

Run three decision scenarios

Keep the first forecast as the base case. Create a collection-delay case by moving one or two important receipts later, and a commitment case by adding the proposed hire, equipment purchase or supplier deposit. Change only the assumptions relevant to the decision so you can see what created the difference.

Use the Cash Flow Forecast Calculator for a quick monthly view, then download the free 13-week cash-flow workbook for the weekly detail. Check the lowest closing balance in each scenario, the first week below your safety buffer and the largest payment that drives the change.

Set actions before the warning arrives

Choose a cash floor and write the response in advance. Crossing the first threshold might trigger invoice follow-up and a pause on optional spending. A lower threshold might require supplier discussions, a revised hiring date or an early conversation with a finance provider or adviser.

Refresh the forecast every week by replacing estimates with cleared transactions, rolling the horizon forward and recording why large variances occurred. This guide supports business planning; it is not accounting, tax or funding advice. Use current records and professional advice where a decision could affect the business materially.