How to build a rolling 13-week cash flow forecast

Thirteen weeks is one quarter at weekly resolution - long enough to see a cash squeeze coming and short enough that the numbers are grounded in actual invoices and bills rather than guesses. It is the horizon lenders, restructuring advisers, and CFOs use to manage liquidity through a tight patch.

1. 1Start with the current bank balance as week-zero opening cash.
2. 2Lay out 13 weekly columns with beginning cash, inflows, outflows, and ending cash.
3. 3Drive inflows from AR: expected collections by invoice due date and payment history.
4. 4Drive outflows from AP, payroll runs, rent, debt service, and tax payments by their actual dates.
5. 5Roll ending cash from one week into the next week beginning balance.
6. 6Each week, drop the oldest week and add a new week 13 so the window keeps rolling.

A forecast you never check against reality drifts. Each week, compare what actually landed to what you projected and note why collections or payments moved. Over a few cycles this tightens your assumptions - especially how quickly customers actually pay versus their terms.

• AR aging and invoice due dates feed the collection line automatically instead of manual estimates.
• Scheduled bills and payroll runs populate the outflow rows from the same ledger.
• The cash-flow projection updates as invoices are paid and bills are scheduled, so the forecast never goes stale.
• Scenario planning lets you branch a downside case - slower collections, a delayed raise - and see the effect on the runway.