Guides · 15 October 2026

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The 13-week cash flow forecast: a simple guide for small business owners

Your profit and loss tells you what happened. A 13-week cash flow forecast tells you what is about to happen, while there is still time to do something about it.

Why 13 weeks

Thirteen weeks is one quarter. It’s long enough to catch your next BAS, a super payment and a slow month, and short enough that the numbers are realistic. Update it weekly and it rolls forward with you.

What goes in it

• Opening cash: what’s actually in the bank this Monday.
• Cash in: when customers will really pay, not when you invoice. Use your actual debtor days.
• Cash out: wages, rent, suppliers, loan and lease repayments, owner drawings.
• The quiet ones: GST and PAYG on the BAS, superannuation, income tax instalments, insurance renewals, registrations.
• Closing cash: opening plus in minus out. This week’s closing is next week’s opening.

How to build it in an hour

1. Make 13 columns, one per week, starting this Monday.
2. Put the big fixed items in first: wages, rent, loans.
3. Add the BAS and super due dates from your calendar.
4. Forecast customer receipts from your aged debtors list and pipeline.
5. Look for the lowest closing balance. That week is your problem week.

What to do with it

If a week dips below your comfort level, you have options while it’s still weeks away: chase invoices earlier, move a purchase, talk to a supplier, set up a payment arrangement or arrange finance. Each one is easier with notice.

Each Monday, ten minutes

Replace last week’s forecast with actuals, add a new week 13, and see whether the problem week moved. That habit alone puts you ahead of most businesses your size.

For a quick start, try the tax health check for a rough tax set-aside figure, and our BAS habits guide for due dates.

Quick answers

What is a 13-week cash flow forecast?

A week-by-week projection of cash in and cash out for the next quarter, updated weekly so it always looks 13 weeks ahead.

What do people forget to include?

GST and PAYG on the BAS, superannuation, income tax instalments and annual bills like insurance.

General information only. This doesn’t take your circumstances into account and isn’t tax, financial or legal advice. Talk to your accountant or registered tax agent before acting. PRM is not a registered tax agent; tax agent services are provided by Australian Tax & Super Pty Ltd (TPB 25291395).