A profit and loss statement tells you whether the business made money last month. It does not tell you whether you can make payroll in six weeks. That gap is where otherwise healthy businesses get into trouble - profitable on paper, short of cash on a Thursday. The 13-week cash flow forecast exists to close it. It is the single most useful management tool we build for clients, and you can set one up in an afternoon.
Why 13 weeks
Thirteen weeks is a quarter: far enough ahead to see a problem while you can still do something about it, close enough that the numbers are real rather than aspirational. Beyond 13 weeks you are forecasting; inside it you are scheduling. The forecast is also rolling - every week you drop the week that has passed, add a new week 13 at the far end, and replace last week’s estimate with what actually happened.
The structure: one column per week, cash in, cash out, closing balance
Open a spreadsheet. Columns are weeks, starting with this one. Rows come in three blocks.
Opening bank balance. The actual cleared balance on Monday morning across every operating account. Not the ledger balance, the bank.
Cash in. One row each for: receipts from existing debtors (take the aged receivables report and place each invoice in the week you genuinely expect it to be paid, not the week it is due); receipts from sales you have not invoiced yet (by week, based on your pipeline and typical payment terms); and other inflows - GST refunds, grants, loan drawdowns, asset sales.
Cash out. Separate rows for the things that are large or fixed in time: wages (per pay run, in the week they are paid); super (now within seven business days of each payday under Payday Super - so it sits in the same or following week as wages, not at quarter-end); PAYG withholding and GST via the BAS or IAS in the week they fall due; payroll tax; rent; loan repayments; insurance; then supplier payments from the aged payables report, placed in the week you intend to pay them; and a line for everything else, estimated from the last three months.
Closing balance = opening + in − out. It becomes next week’s opening balance. Add one more row: the minimum balance you are prepared to operate on - your buffer. Any week where closing drops below it is highlighted. That highlight is the whole point of the exercise.
What goes wrong when people build their first one
- Dating receipts by due date. If your customers pay on average 12 days late, the forecast must say so. Use the actual average days-to-pay for each major customer; the cash conversion cycle brief explains how to find it.
- Forgetting the lumpy items. The quarterly BAS, the annual insurance premium, the payroll tax reconciliation in July, the Christmas close-down wages. These are exactly the weeks the forecast is for.
- Mixing GST in and out of figures. Pick one convention - we use GST-inclusive for every receipt and payment, with the BAS payment as its own line - and hold to it.
- Building it once. A forecast that is not rolled forward each week is a snapshot that was wrong by Wednesday.
The Monday routine
Twenty minutes, every week, same time. Enter the actual opening balance. Replace last week’s estimates with actuals and note the variances - which customer paid late, which supplier payment slipped. Roll the columns. Then look only at the buffer line: is any week in the next 13 below it? If yes, you have the one thing a bank balance never gives you - time.
Three signals that mean act now, not later
The dip. A single week below buffer, usually where a BAS payment or payroll tax lands on the same week as a large supplier run. The fix is sequencing: bring a receipt forward with an early-payment call, or move a discretionary payment one week later. This is an ordinary, solvable problem - but only if seen three weeks out.
The slope. The closing balance trends down across the 13 weeks even though no single week breaches. This is a structural gap between what you collect and what you spend, and it will not sequence away. It needs a pricing, cost or collections decision, and it needs it this quarter.
The cliff. Week 13 shows a balance you cannot cover, driven by a known event - a loan maturity, a tax payment, a large contract ending. Six to twelve weeks is enough notice to arrange an overdraft, negotiate terms or restructure a payment with the ATO. Six days is not.
Where this sits with the rest of your reporting
The 13-week forecast does not replace the monthly management pack; it sits beside it. The P&L tells you whether the business model works. The forecast tells you whether you will be there to find out. Together with a break-even calculation and a clean aged receivables report, it is most of what a board or a lender wants to see before they ask anything else.
If you would like a forecast built on your own numbers and then run for you each week, that is a standard part of our Fractional CFO and Growth-tier engagements. The template is simple; the discipline of rolling it every Monday is what makes it work.
References: Standard 13-week direct-method cash flow forecasting practice as used in corporate treasury and turnaround work; ATO - BAS, PAYG instalment and Payday Super payment timing. Current at 11 September 2026.
This information is general in nature and does not constitute personal financial or tax advice. Please contact us to discuss your individual circumstances. Tax laws are subject to change; information on this page reflects legislation in effect as of September 2026.