13-Week Cash Flow Forecast: How Founders Build One
A 13-week cash flow forecast is a week-by-week view of the cash that will actually hit your bank over the next quarter. It shows which week your balance gets dangerously low, while you can still act.
- Horizon
- 13 weeks, one quarter, updated every week
- What it tracks
- Cash received and cash paid, in the week it actually moves
- Main use
- Spot a low-cash week early enough to fix it
15+ years in finance: 100+ financial models built, €40m+ raised for clients, Forbes contributor and lecturer.
Short answer: a 13-week cash flow forecast is a week-by-week view of the cash that will actually enter and leave your bank account over the next quarter. Its job is simple: show you which week your balance gets uncomfortably low while you still have time to act.
Why 13 weeks
Thirteen weeks is one quarter. That is far enough ahead to fix a problem, for example by chasing invoices, moving a supplier payment or arranging a credit line. It is also close enough that your estimates stay realistic, because you know most of your customers, payroll and bills for the next three months.
A longer financial model is useful for strategy. The 13-week forecast is the tool for day-to-day survival and short-term decisions.
The basic structure
Each column is one week. Each week has the same five lines:
| Line | What goes in |
|---|---|
| Opening cash | Bank balance at the start of the week |
| Cash in | Customer payments and other inflows |
| Cash out | Payroll, suppliers, rent, taxes, loan repayments, software |
| Net movement | Cash in minus cash out |
| Closing cash | Opening plus net movement; it becomes next week's opening cash |
Inputs you need
- Your real bank balance today
- A list of unpaid customer invoices with due dates and, ideally, how each customer usually pays
- A list of supplier bills and their due dates
- Your payroll calendar
- Tax, VAT and social contribution dates
- Loan, lease and card repayment schedules
- Known one-off items, such as annual subscriptions or equipment
How to build it
- Start from the actual bank balance, not from the accounting system.
- Put each customer receipt in the week you expect the cash, not the invoice date. Use real payment behaviour, not payment terms.
- Put each payment in the week it leaves your account.
- Add recurring costs for all 13 weeks.
- Calculate closing cash for every week.
- Set a minimum cash buffer and highlight every week that falls below it.
Keep it honest
A forecast that is never compared with reality quickly becomes fiction. Each week, replace the forecast with the actual bank movements, note the biggest differences and ask why. Over time you learn how late your customers really pay.
Common mistakes:
- Using invoice dates instead of expected payment dates
- Forgetting taxes, VAT or annual payments
- Mixing profit with cash (a profitable month can still be a cash-negative one)
- Assuming every large customer pays on time
What to do when a low week appears
A weak week 7 is useful information, because you have seven weeks to respond. Typical levers include collecting overdue invoices, asking for deposits, agreeing new payment dates with suppliers, pausing non-essential spending or arranging short-term funding. Which lever fits depends on your business, contracts and costs, so test each one in the forecast before you act.
Book a CFO diagnostic call - 30 minutes, no pitch, a real CFO.
Related questions
Why 13 weeks and not 12 months?
Thirteen weeks is far enough ahead to fix a problem and close enough for your estimates to stay realistic. A 12-month forecast is better for strategy; the 13-week view is the tool for short-term cash decisions.
How is it different from a P&L forecast?
A P&L forecast follows revenue and costs when they are earned or incurred. A 13-week cash forecast follows money when it moves, so a sale paid in 60 days appears 60 days later.
How often should I update it?
Weekly. Replace last week's forecast with actual bank movements, note what changed and roll the forecast forward by one week.
