Formula
closing cash = opening cash + receipts − payments, rolled forward one week at a time for 13 weeks
13-week cash flow forecast
A 13-week cash flow forecast projects cash coming in and going out week by week over the next quarter, the horizon where a business can still act before a shortfall arrives.
The method comes from turnaround and restructuring practice, where it is the standard document lenders and advisors ask for when cash is tight, and it earned that role for a reason: 13 weeks is one quarter, far enough out to act on and near enough to predict honestly.
The weekly grain is the point. A monthly forecast can show a positive month that hides a fatal week inside it, because payroll leaves on the 25th and the big invoice arrives on the 30th. Weekly resolution surfaces exactly those timing collisions, which are how businesses that are profitable on paper still bounce payments.
It works as a discipline, not a document: each week the oldest week drops off, a new week is added, and last week's forecast is compared with what actually happened. The forecast-versus-actual gap is where you learn whether your assumptions about customer payment behavior are true.
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Plainhub computes 13-week cash flow forecast from money you record in plain words, so it is current when you need it rather than the night before a board meeting.
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