The thirteen-week forecast, built and maintained

Thirteen weeks is a quarter, in the unit that matters. Monthly is too coarse, because a business can be fine in a month and still be unable to pay wages in the third week of it. Annual is a plan, not a forecast. And thirteen weeks is far enough ahead that you can still do something about what you see, which is the only reason to build it.

The build is simple and the discipline is not. One row for the opening balance. Then everything you expect to come in, by the week you expect it to actually arrive, not the week you invoice — a customer on forty-five day terms who has never once paid on time goes in at sixty. Then everything going out, by the week it actually leaves: wages, rent, suppliers, tax payments, loan repayments, the annual insurance that always surprises people. Closing balance carries to the next week. That is the whole model, and a spreadsheet is the right tool for it.

What makes it useful is updating it, once a week, forever, and moving the window forward so it always looks thirteen weeks out. Twenty minutes on a Monday. The value is not in the forecast being right — it will not be — but in the fact that being wrong shows up early, while there are still options. A forecast built once and admired is an exercise. A forecast maintained is an early-warning system.