Interest Rate Rise? Build a 13-Week Cash Flow Forecast That Models It

Last reviewed: November 2026

Each time the Reserve Bank moves, owners ask the same question: what does this do to my cash? The honest answer is that nobody can tell from the headline rate. It depends on what you owe, who owes you, and when your fixed bills fall. The only way to see it is to put those numbers in a forecast, week by week, and look at the lowest point. This guide sets out what that forecast should model after the November 2026 rise. It is also the kind of recurring finance work that Agentive's dedicated AI Employee is built to keep current, so the forecast stays a tool rather than a one-off spreadsheet.

What did the RBA do to interest rates in November 2026?

The RBA raised the cash rate target by 25 basis points to 4.85 per cent. In its Monetary Policy Board statement of 3 November 2026, the Board said inflation remains elevated and broadly based, and that the inflation outlook had been revised materially higher. The decision was by majority: six members voted to increase the rate and three voted to leave it at 4.60 per cent.

It was the fifth increase this year. The RBA's cash rate target table shows rises of 25 basis points effective in February, March, May, September and November 2026, taking the target from 3.60 per cent to 4.85 per cent, a total of 1.25 percentage points. The Board now expects inflation to stay above 3 per cent for the coming year and not to reach the top of its 2 to 3 per cent target range until late 2027.

Two parts of the statement matter directly for small business cash flow. The Board said: "Liaison indicates that many firms are experiencing cost pressures and are either increasing the prices of their goods and services in response or looking to do so." It also said: "The economy is slowing, housing prices have fallen significantly and the unemployment rate has risen." Put plainly, your suppliers may be raising prices while your customers are under more pressure. Both belong in the forecast. The next scheduled meeting, according to the RBA's board meeting schedule, is 7 and 8 December 2026.

Why use a 13-week cash flow forecast when rates are rising?

Because it is built from facts you already have, not from guesses about the economy. Over the next 13 weeks, most of a small business's cash movements are already known: invoices issued and their due dates, bills received, payroll dates, loan repayments, the next BAS and any instalments. That makes a quarterly, weekly forecast far more accurate than an annual budget, and it shows a shortfall early enough to do something about it.

Weekly matters as much as 13. A monthly forecast hides the week where payroll, a quarterly BAS payment and a loan repayment all land before the large customer pays. The month looks fine on paper while the account sits below zero for six days.

What should a cash flow forecast model after an interest rate rise?

It should model every line a rate rise can move, not just the loan. The table below is Agentive's suggested checklist for Australian small businesses. It is a planning aid, not financial advice, and the right assumptions depend on your business and lender.

The customer receipts row is the one most forecasts get wrong. A forecast that assumes every invoice is paid on its due date is a forecast of what you hope will happen. Use each customer's actual history: if a client on 30-day terms has paid in 52 days for the last six months, forecast 52. Our collections playbook for clients who pay in 70 days covers how to shorten that gap rather than just record it.

How much does a rate rise add to business loan repayments?

Less than most owners fear on any single rise, and more than they expect across a year of rises. Here is a simplified worked example, using a hypothetical business with a $300,000 interest-only variable loan whose lender passes on each rise in full.

• One 0.25 percentage point rise adds about $750 a year, or about $62.50 a month.
• The five rises in 2026, 1.25 percentage points in total, add about $3,750 a year, or about $312.50 a month, compared with January.

These are approximations. Principal and interest loans, fees and how the lender calculates interest all change the result, and lenders set their own rates rather than following the cash rate automatically. Use the figure on your lender's repayment notice. For many small businesses the loan change is real but manageable; the bigger risks usually sit in the receipts and ATO lines.

Should a small business use the ATO as a line of credit when rates rise?

No. An unpaid ATO debt is now one of the most expensive forms of finance a small business can carry. The ATO's general interest charge rates page sets the GIC annual rate at 11.51 per cent for October to December 2026, a daily rate of 0.03153425 per cent. GIC is updated each quarter.

The after-tax cost has also changed. The ATO's page on the law change to deny deductions for ATO interest charges says GIC and shortfall interest charge incurred on or after 1 July 2025 are not deductible, regardless of whether the debt relates to an earlier income year. As a rough illustration, $20,000 left unpaid for 90 days at the current daily rate, compounding daily, accrues about $576 in GIC, with no deduction for it.

If the forecast shows you cannot meet a tax payment, the ATO's guidance on payment plans is the place to start. The ATO says tax debts on a payment plan continue to accrue GIC, which compounds daily, that income tax and activity statement accounts need separate payment plans, and that you must pay future tax debts in full and on time. Seeing the shortfall in week 3 of a forecast gives you time to arrange that properly instead of discovering it on the due date. Keeping the BAS itself on time is easier when the preparation is routine, which we covered in how to automate BAS preparation in Australia.

How does Payday Super change the cash flow forecast?

It turns super from a quarterly lump into a line that follows every payday. The ATO's guide to managing the changeover to Payday Super says that from 1 July 2026, employers pay super guarantee for each payday instead of quarterly, and contributions are due in employees' super accounts within 7 business days after payday, unless a longer period applies, such as for new employees.

For the forecast, that means super sits in the same week as wages or the week after, rather than in a quarterly spike. Some businesses used the old quarterly timing as an informal buffer. That buffer has gone. If your forecast template was built before July 2026, check that super is now modelled per pay run.

How do you build a 13-week cash flow forecast?

Start from the real bank balance and work forward one week at a time. These steps work for a spreadsheet or for a forecasting tool connected to your accounting software:

1. Set the opening balance. Use the actual combined balance of your business bank accounts today, not the ledger balance. Reconcile first if the two differ.
2. Lay out 13 weekly columns. Each column has receipts, payments and a closing balance that becomes the next week's opening balance.
3. Forecast receipts by customer. List open invoices and expected new sales, and place each in the week it is likely to arrive based on that customer's payment history.
4. Add fixed payments on their dates. Wages, super, PAYG withholding, rent, loan repayments and the next BAS go in first, because they cannot move.
5. Add supplier payments. Use bills received plus known regular costs, with any price increases suppliers have told you about.
6. Update interest costs. Apply the new loan repayment from the date your lender says it applies, and interest on the forecast overdraft balance.
7. Set a minimum buffer. Decide the lowest balance you are comfortable holding, for example two weeks of wages and fixed costs, and mark any week below it.
8. Build a stress case. Copy the base case, push your three largest customers out by 30 days, add another rate rise from the next RBA meeting, and see where the low point moves.
9. Decide actions for any red week. Chase a specific invoice, move a discretionary purchase, talk to the lender about the limit, or contact the ATO early.
10. Roll it forward every week. Replace last week's forecast with actuals, add a new week 13, and note why any line was off.

Step 1 depends on clean books. If bank transactions are coded to the wrong accounts, the forecast inherits the mess. A tidy, consistent chart, like the one in our standard chart of accounts for Australian small business, makes the categories in the forecast match the categories in the ledger, which is what lets you compare forecast to actual each week.

What should a cash flow stress test include?

A stress test should combine the things that tend to go wrong together, not test them one at a time. When rates rise and the economy slows, a slower large customer, a supplier price rise and a higher repayment often arrive in the same quarter. Agentive suggests three scenarios for most small businesses:

• Base case: customers pay as they have over the last six months, current loan repayments, known supplier prices.
• Rate case: base case plus a further 0.25 percentage point rise from the next RBA meeting, passed on by your lender.
• Stress case: rate case, plus your largest three customers paying 30 days later and your main supplier raising prices by an amount you choose.

The point is not to predict the RBA. The Board itself says there are heightened uncertainties about the outlook. The point is to know, in advance, which week breaks first and what you would do about it. If the stress case never goes below your buffer, you can stop worrying about the headlines. If it does, you have a list of actions and a date to take them by.

Why do most small business cash flow forecasts go stale?

Because updating them is tedious, and the person who built the forecast has other work. Rolling it forward means pulling the bank balance, checking which invoices were paid, adding new bills and rechecking assumptions. That hour keeps losing to more urgent jobs, until the forecast is six weeks old and nobody trusts it.

This is where Agentive's view is firm: a forecast is a weekly process, not a document. Agentive's AI Operation Engine for finance works inside Xero, MYOB or QuickBooks, generates reports, monitors cash flow and sends payment reminders. In a forecasting process that means the repetitive parts, such as refreshing receipts and payments from the ledger, updating the actual balance and flagging customers paying later than usual, can be prepared every week for a person to review. Our guide to automating debtor chasing covers the follow-up side, and AI bookkeeping for Australian businesses covers keeping the ledger clean enough to forecast from.

The judgement stays with people. Which assumptions to use for the next rate decision, which payments to delay and when to call the lender are decisions for the owner, bookkeeper or accountant. That split, AI preparing and a person reviewing, is the model we set out in human-in-the-loop review checkpoints for AI bookkeeping. And because a forecast touches every customer, supplier and loan figure in the business, where the work runs matters: Agentive's AI Employee runs on a dedicated single-tenant server on AWS Sydney, with client data stored onshore and never used to train models.

Forecast the week, not the headline

The November 2026 rise to 4.85 per cent will not affect every small business in the same way. A business with little debt and fast-paying customers may barely notice it. A business with an overdraft, a slow-paying major customer and a BAS due next month might feel it within weeks. A 13-week forecast that models loan repayments, real customer payment patterns, supplier prices, Payday Super and ATO due dates tells you which one you are. Update it every week, run a stress case before each RBA meeting, and act on the first red week rather than the last. If keeping it current is the hard part, that is the work dedicated AI for business owners is designed to take off your desk.