How to build a 13-week cash flow forecast
A 13-week cash flow forecast shows, week by week for the next quarter, how much cash comes in, how much goes out, and what is left. It is the tool finance teams use to spot a tight week before it arrives.
Why 13 weeks
Thirteen weeks is one quarter. It is long enough to see payroll cycles, rent, quarterly tax payments and slow-paying customers, and short enough that the numbers come from real invoices and bills rather than guesses. Monthly budgets hide timing; a weekly view shows the week you actually run short.
The five building blocks
- Opening cash. Start from the bank balance on the first day of week 1. Use the bank, not the general ledger.
- Receipts. List open customer invoices (your accounts receivable aging) and place each one in the week you realistically expect to collect it, not the due date. Add recurring receipts such as subscriptions or rent you collect.
- Disbursements. List open vendor bills (accounts payable) in the week you plan to pay them, then add recurring outflows: payroll, rent, loan payments, insurance, software, and taxes.
- Closing cash. Closing cash = opening cash + receipts − disbursements. Each week's closing cash becomes the next week's opening cash.
- Minimum cash buffer. Pick the lowest balance you are comfortable holding (for example, two weeks of payroll). Flag any week that falls below it.
Opening cash (week n+1) = Closing cash (week n)
A worked week
| Week 1 | Amount |
|---|---|
| Opening cash | $85,000 |
| + Customer receipts | $42,000 |
| − Payroll, rent, vendor bills, loan payment | $51,500 |
| = Closing cash | $75,500 |
The numbers are illustrative. If your buffer is $60,000, week 1 is fine; the forecast's job is to show whether week 6 or week 9 is not.
Keep it rolling
- Every week, replace the oldest week's forecast with actuals and add a new week 13.
- Compare forecast to actual for receipts and disbursements. Large misses tell you which assumption to fix, usually collection timing.
- Run a downside case: delay your two largest receipts by two weeks and see whether you still clear the buffer.
Common mistakes
- Using invoice due dates instead of when customers actually pay.
- Forgetting non-monthly items: annual insurance, quarterly estimated taxes, bonuses.
- Mixing accrual numbers (revenue, expense) with cash. The forecast tracks cash only.
Skip the build: 13-Week Cash Flow Forecast Pro
Everything in this guide is already wired up in a tested Excel and Google Sheets template, with a filled-in example and a blank copy. Formulas are fully visible, with no passwords and no hidden sheets.
For planning and information only. Not financial, tax, legal or investment advice.