Cash Flow
Building a 13-week cash forecast that operators actually use
· 7 min read
Most forecasts die in a spreadsheet nobody opens. We break down a rolling model that ties to real receivables and payables — and stays accurate enough to trust.
A forecast nobody opens is not a forecast
The usual 13-week model is a spreadsheet with last month's collections copied forward, a hope for new sales, and a lump of 'other' that hides payroll timing. It looks precise. It is not used, because the first week it misses actual cash, operators stop trusting it.
A forecast that operators use has to be boring: it should start from invoices you have already sent and bills you have already approved, then layer only a few explicit assumptions on top.
Tie the model to the ledger, not to a budget
Open AR with expected collection dates is the right starting point for inflows. Open AP with due dates is the right starting point for outflows. Payroll, rent, tax, and debt service are known cadences. Everything else is a residual, not the core of the model.
When the forecast is rebuilt from live receivables and payables each week, you stop reconciling the spreadsheet to the books. The books are the forecast.
Roll it every week, do not rebuild it
Drop the week that just closed. Add a new week thirteen. Update collection status on large invoices. That is the whole ritual. If updating the model takes more than thirty minutes, it is too handmade to survive a busy month.
The decision the forecast should support is simple: can we take this vendor early-pay discount, hire this contractor, or do we need to pull collections this week? If the model cannot answer that by Tuesday, it is too late.
Show pressure, not a single number
A single ending-cash figure hides timing. Operators need the weekly trough. A company can be profitable on a P&L and still miss payroll because two large customers pay on day 50 and rent hits on day 1.
Modern Accounting AI's 13-week view is built from real AR and AP so the trough is visible before it is urgent, not after the checking account is already tight.