The 13-week cash flow forecast: how to see a cash crunch coming

Most owners manage cash by looking at the bank balance. It feels like the right instrument, because it’s real money and it’s current. But the balance only tells you what has already happened: every invoice that’s been paid, every wage run that’s cleared. It says nothing about the week in late October when the quarterly BAS, an insurance renewal and a slow-paying customer all arrive together.

Businesses almost never run out of cash suddenly. The week that hurts was sitting there, visible, six or eight weeks out. Nobody was looking at it. The tool for looking at it is the 13-week cash forecast, and it’s simpler than the name suggests.

What it actually is

One page, thirteen columns, one per week. Each column answers the same three questions: what do we start the week with, what’s coming in, what’s going out. The running balance along the bottom is the punchline. Somewhere in those thirteen numbers is your lowest week, and that number, not today’s balance, is the one that should shape your decisions this month.

Why thirteen weeks? Because it’s a quarter, and because it’s the window where you’re forecasting things you mostly already know. Next week’s wages aren’t a guess. The rent isn’t a guess. The invoices you’ve already issued have due dates on them. Push much past a quarter and you’re forecasting sales you haven’t made yet, which is a different exercise for a different day.

Start with what you hold and what’s coming in

Opening cash. Today’s cleared balance across your operating accounts. Not the ledger figure in Xero, the money the bank will actually let you spend.

Receipts. When customers will actually pay, not when they should. If your terms say 30 days and your biggest customer pays at 45, the forecast uses 45. This is where most first drafts flatter themselves, and it’s worth being pessimistic on purpose. In a services firm, map each retainer and each project milestone to the week the cash lands. In construction, it’s the progress claim cycle and the certifier’s clock.

What goes out, and when

Payments are the easier half because so many of them are fixed: wages and super each cycle, rent, loan repayments, the ATO on its dates, supplier bills on their terms. The trap is the lumpy stuff. Annual insurance premiums, software renewals, equipment purchases and the BAS have a habit of clustering, and a forecast that spreads them evenly across the quarter will look calmer than your bank account ever will. Put each one in the week it actually falls.

Then rebuild the whole thing weekly. Drop the week that just finished, add a new week thirteen, and take two minutes to compare what happened against what you’d forecast. That comparison is the point. A static forecast built once in July is stale by August; a rolling one gets more honest every week, because your own payment patterns keep correcting it.

When it shows a week you don’t like

This is the payoff. A tight week seen six weeks early is a management task, and the levers are ordinary: bring invoicing forward, chase the debtor who’s drifting, ask a supplier for one longer run of terms, push a discretionary purchase back a fortnight. A tight week discovered on the Monday it arrives is a crisis, and the levers left are the expensive ones.

The forecast also changes the quality of your growth decisions. Hiring ahead of billing, taking on a bigger job, buying stock for a busy season: each of these is a bet that near-term cash can carry the cost until the revenue lands. The 13-week view is where you check the bet before you place it.

If the forecast keeps showing the same tight pattern quarter after quarter, the problem usually isn’t timing but structure: too much cash sitting in working capital, lent out to customers or parked in stock and work in progress.

Make it a rhythm, not a project

Like most cash discipline, this fails as a one-off and works as a routine. The version that helps is the one someone rebuilds every week and an owner reads every month, alongside the questions that matter: where’s the low week, how many weeks of cover do we hold, and was last month’s forecast roughly right?

That rhythm is exactly the kind of thing a proper monthly finance function exists to run, and it’s one of the first things we stand up with a new client. But you don’t need us to start. A spreadsheet, thirteen columns and a standing Friday appointment with it will put you ahead of most businesses in Brisbane by next quarter.

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