Academy
The 13-week cash flow forecast: how to build one and what it tells you
Why 13 weeks
Monthly cash forecasts hide the problem. A month can start and end with the same balance while dropping $140,000 below zero in week three when payroll, sales tax and a supplier deposit land together. A weekly view over one quarter catches that. Beyond 13 weeks the inputs get soft and the forecast turns into a budget, which is a different tool.
The layout
| Row | Weeks 1 to 13 |
|---|---|
| Opening cash | Last week's ending cash (week 1: today's bank balance) |
| Receipts: customer collections | By customer or draw, dated by when they actually pay, not when invoiced |
| Receipts: other | Loan draws, tax refunds, asset sales |
| Disbursements: payroll and payroll tax | Fixed dates, the biggest line for most companies |
| Disbursements: AP and vendor payments | From the bills in BILL or the AP aging, dated by due date |
| Disbursements: rent, debt service, insurance, sales tax | Fixed dates |
| Disbursements: owner draws and distributions | Planned, not improvised |
| Ending cash | Opening plus receipts minus disbursements |
| Available line of credit | Ending cash plus undrawn line |
Mark the lowest ending cash in the 13 weeks. That number, and the week it lands, is the forecast. Everything else is support.
How to build it from the ledger
- Start with the reconciled bank balance. If the books are not reconciled through last week, reconcile first; a forecast from an unreconciled balance is wrong before you start.
- Pull the AR aging and date each receivable by when that customer actually pays, from history, not from terms. Contractors: date draws by the owner's pay cycle and hold retainage until release.
- Pull the AP aging and the bills in BILL, dated by due date.
- Lay in the fixed calendar: payroll, payroll tax, rent, loan payments, insurance, sales tax.
- Add what is known but not yet in the ledger: the equipment deposit, the hire starting in week 6, the quarterly estimate.
- Roll it forward every week: replace week 1 with actuals, add a new week 13, and note what changed.
What owners do with it
- Time a purchase. The truck can wait until week 6 without touching the line; week 3 cannot.
- Size the line of credit. The low point over four rolling quarters is the line you need, plus a margin.
- Decide on a hire. A $90,000 controller costs about $2,100 a week loaded, starting the week they start. Put it in and watch the low point.
- Call two customers. When the low point is driven by two slow receivables, the forecast tells you which two.
- Sleep. The most common comment from an owner after the first forecast is that they stopped checking the bank balance every morning.
Construction notes
Retainage goes in as a receipt in the week it is expected to be released, not when earned. Over-billings are cash you already have and will spend on the job; the forecast should show the cost to finish those jobs even though no receipt is coming. Under-billings are receipts the forecast can pull forward by billing them this draw.
ProvenCFO's CFO Foundation tier includes the 13-week forecast, updated monthly and weekly in a crunch, built from the live ledger.
Questions people ask
How accurate is a 13-week cash flow forecast?
Weeks 1 to 4 are usually within 5% once the receivable timing is based on history. Weeks 9 to 13 are directional. The value is in the rolling update: every week the near-term gets re-anchored to actuals.
Can I build it in a spreadsheet?
Yes, and most are. ProvenCFO builds it in Google Sheets or Excel tied to the ledger so the AR, AP and payroll lines pull rather than being retyped.
How is it different from a budget?
A budget is annual, accrual, by month, and about profit. The 13-week forecast is weekly, cash, and about timing. Companies need both; the forecast is the one that keeps the lights on.
Who should own it?
The controller or CFO updates it; the owner reads it weekly. If nobody has read it in two weeks, it is not being used.
Written by the people at ProvenCFO who do the work: fractional CFOs, controllers and bookkeepers for American owner-led companies.
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