How Do I Build a Cash Forecast I Can Trust?

Most cash forecasts fail for one of two reasons: they are built once and abandoned, or they are built from the income statement instead of the bank account. A forecast you can trust is a living document, denominated in actual receipts and payments, maintained on a rhythm.

The standard instrument is the 13-week rolling forecast — long enough to see a quarter ahead, short enough to stay honest, weekly enough to catch trouble while it is still small.

The construction is disciplined simplicity: start with the confirmed bank balance; add expected receipts by week — based on which specific invoices are due and how customers actually pay, not on when sales are booked; subtract committed payments by week — payroll, rent, remittance deadlines, loan payments, supplier runs; and carry the closing balance forward as next week's opening. The output is a single line — projected cash by week — and the discipline is the weekly variance review: what did we predict, what happened, and why.

Trust is built through calibration. After a month of comparing forecast to actual, you learn your real collection patterns (the customer who says 30 days and pays in 55), your real payment slippage, and your own optimism bias — and the forecast tightens. From there it becomes a decision instrument: the week you will dip below your minimum balance is visible six weeks out, while every option — accelerating collections, deferring discretionary spending, drawing the line of credit — is still cheap.