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13-week cash flow forecast: how to build one that ties to the bank
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Book a callA 13-week cash flow forecast is a week-by-week plan of your cash for the next quarter. It starts from the actual bank balance, then adds expected customer receipts and takes away supplier payments, payroll and other cash going out. Updated and tied to the bank every week, it shows the exact week a cash gap would hit, not just the month.
- A 13-week cash flow forecast starts from the bank balance, not the income statement.
- Tie closing cash to the bank every week, then drop the old week and add a new one.
- We run client forecasts over 16 weeks, for 3 more weeks of warning.
What is a 13-week cash flow forecast?
A 13-week cash flow forecast shows your cash one week at a time for the next quarter. It starts from the real bank balance, not from the income statement. Each week adds the cash you expect in and takes away the cash going out. You see the exact week a gap would hit.
A month can look fine on paper. One week inside it can still run dry. That is the week a monthly forecast hides.
How do you build a 13-week cash flow forecast? (the 7 steps)
You build a 13-week cash flow forecast by filling 13 weekly columns with real numbers. Start with cash in the bank. Add the receipts you expect. Take away the payments you owe. Every cell comes from a source document, not a guess.
- Take the opening balance from the bank statement, not the ledger.
- List customer receipts by week from the AR aging, invoice by invoice.
- List supplier payments by week from the AP aging and your payment runs.
- Add payroll, rent, debt service and tax on the dates they leave the bank.
- Add one-off items: a loan draw, an equipment purchase, a refund.
- Work out each week’s closing cash. It becomes next week’s opening cash.
- Each week, tie closing cash to the bank, drop the week that passed and add a new week 13.
These are example numbers. Week 1 opens with $400,000 in the bank. Customers pay $180,000. Payroll and suppliers take $150,000. A loan payment takes $20,000. Closing cash is $400,000 plus $180,000, minus $150,000, minus $20,000, which is $410,000. That $410,000 must match the bank before you start week 2.
Look at last week’s forecast. Did anyone tie the closing balance to the bank statement before it went out?
13-week forecast vs 12-month rolling forecast: which do you need?
They answer different questions. A 13-week cash flow forecast tracks real cash week by week, so it is built for near-term risk. A 12-month rolling forecast moves forward one month at a time and supports planning and board reporting. You may well need both. The 13-week one warns you in time.
| Item | 13-week cash flow forecast | 12-month rolling forecast |
|---|---|---|
| Looks ahead | 13 weeks, about one quarter | 12 months, moving forward |
| Built from | Bank, receivables, payables, payroll | Budget and income statement |
| Used for | Managing cash in the near term | Planning and board reporting |
| Updated | Every week | Every month |
Neither one is the cash flow statement in your financials. That report looks back. It sorts past cash into operating, investing and financing activities, as KPMG’s handbook on the statement of cash flows sets out.
We run client forecasts as a 16-week rolling cash forecast. The 3 extra weeks give more warning before a gap.
Can ChatGPT build a cash flow forecast for you?
ChatGPT can draft the template and suggest formulas. It cannot check a single number against your bank, your customer ledger or your payroll. A 13-week cash flow forecast is only as good as the data behind it. A chat tool sees none of that data unless someone feeds it in and checks what comes out.
AI is good at the repetitive part: pulling transactions, filling the grid, flagging a week that moved. The check still needs a person. That is how we work in AI accounting: AI does the repetitive work, and a named senior accountant checks and signs every number.
Why do 13-week forecasts break down?
A 13-week forecast breaks down when nobody ties last week’s actual cash to the bank before building the next week. One receipt gets guessed instead of taken from the aging. Every week after that moves further from the truth. An unreconciled payroll or clearing account makes the drift worse.
How do you keep the forecast accurate week after week?
You keep it accurate with one weekly tie-out, done before the forecast goes to anyone. Tie the bank, customer balances, supplier balances and payroll to the penny. One named person signs it off. Then compare last week’s forecast with what really happened, and learn from every miss.
- Opening cash equals the bank statement.
- Last week’s receipts match the AR aging.
- Last week’s payments match the AP ledger and the payroll report.
- Every large difference has a written reason.
- One named person signed the week.
A tied-out forecast becomes the weekly cash report a board can rely on. Our guide on how to build a weekly cash flow forecast covers the basics. If your books are in NetSuite, the month-end close in NetSuite feeds the same tie-out. Book a free 30-minute call and bring one number you don’t trust.
When do you need us, and when can you do it alone?
You can build a 13-week cash flow forecast yourself with a spreadsheet, the AR aging and the AP aging. The hard part is the weekly tie-out, and keeping it up after the first few weeks. That is what our fractional CFO work takes on. AI does the repetitive work. A named senior accountant checks and signs every number. It starts with a free 30-minute call.
Where this goes wrong
| The problem | What it costs you | The fix |
|---|---|---|
| Opening cash is copied from the ledger, not the bank | The whole week is wrong before one line is forecast | Take the opening balance from the bank statement every week |
| Receipts are forecast from the sales pipeline | Collections look too high and hide a real gap | Tie weekly receipts to the AR aging, invoice by invoice |
| Nobody signs the forecast before it goes out | A wrong number reaches the board with no owner | One named person ties out and signs every week |
Based on how we build and tie out a 16-week rolling cash forecast for clients, and on KPMG’s handbook on the statement of cash flows.
Sources we opened and checked for this guide:
Published October 2026. Checked in October 2026. If something here is out of date, tell us and we will fix it.
David Tarkhanyan
