What is the interest rate buffer banks use to test my borrowing capacity?

The interest rate buffer is a margin added on top of your loan’s actual interest rate, used only for the purpose of testing whether you could still afford the repayments if rates rose. Australian lenders don’t assess your home loan application at the rate you’d actually pay today — they test it at that rate plus a buffer. As at July 2026, the minimum buffer required of Australian banks and other authorised deposit-taking institutions (ADIs) is 3.0 percentage points, set under Prudential Standard APS 220, and it’s applied to your new loan and to any existing debts you already carry.

Why test at a higher rate than I’ll actually be charged?

Because interest rates move, and a loan approved only against today’s rate could leave a borrower exposed if rates rise during the life of the loan. The buffer exists so a lender’s assessment reflects not just what you can afford now, but what you could still afford at a higher rate — without needing that rate rise to actually happen for the test to matter. It sits alongside the broader responsible lending obligation in ASIC’s RG 209, which requires a lender to assess whether you could meet your repayments without substantial hardship; the buffer is one of the tools that makes that assessment more resilient to future rate movements, not a one-off checkbox.

Where does the 3.0 percentage point figure come from?

It comes from APRA, Australia’s prudential regulator for banks. APRA’s Prudential Practice Guide APG 223 (Residential Mortgage Lending), current as at July 2026, states it directly:

“Under Attachment C of Prudential Standard APS 220 Credit Risk Management, ADIs must apply a buffer over a loan’s interest rate of at least 3.0 per cent, unless determined otherwise by APRA.”

Two things are worth separating out here. APS 220 is a binding prudential standard — the 3.0 percentage point buffer is a genuine minimum ADIs must apply. APG 223, the document that explains how APS 220 is put into practice, is a practice guide: APRA describes practice guides generally as not themselves creating enforceable requirements. The enforceable obligation is in the standard; the guide explains APRA’s expectations for how it’s carried out. Either way, 3.0 percentage points is a floor, not a target — nothing stops a lender from applying more.

The buffer as a formula: assessed interest rate = actual (or reference) interest rate + a buffer of at least 3.0 percentage points (APS 220, as at July 2026) — applied to the loan being assessed and to your existing debt commitments.

Does the buffer apply to my existing debts too?

Yes. This is one of the more consequential parts of the rule: the buffer isn’t only applied to the new loan you’re seeking. Under the framework APG 223 describes, it’s applied to existing debt commitments as well — other loans, credit cards, and any other credit you’re already servicing are tested at the buffered rate, not the rate you’re actually paying on them today. That’s part of why an existing debt can weigh on a new loan application more heavily than its current repayment might suggest.

This article can’t put a number on how any specific existing debt or credit limit changes a borrowing outcome — that’s a function of a lender’s own serviceability calculator and isn’t published. What’s verifiable is the mechanism: existing debts are tested at the higher, buffered rate, alongside the new loan.

Does every lender apply exactly 3.0%?

Not necessarily. APS 220 sets a minimum of 3.0 percentage points — a lender can choose to apply a larger buffer. APG 223 also describes the buffer as used alongside an interest-rate floor, meaning a lender’s assessment rate may be the higher of the buffered rate or a set floor rate. Exactly how any individual lender combines the buffer, the floor, and its own risk appetite is that lender’s own policy, and isn’t published — this article states the regulatory minimum, not any named lender’s practice.

How does the buffer fit with the rest of a borrowing capacity assessment?

The buffer is one input among several a lender applies — alongside how your income is counted, how your expenses are assessed, and how your existing commitments are treated. See our guide to how banks calculate borrowing capacity for the full picture of how those pieces fit together.

What the buffer doesn’t tell you

The buffer explains part of why a lender’s serviceability assessment produces a smaller number than “salary times some multiple” — but it doesn’t, by itself, tell you what you could borrow. That number depends on your specific income, expenses, existing debts and the individual lender’s policy, none of which this article can calculate for you. A licensed mortgage broker or lender can run the actual assessment, buffer included, against your real figures. For the deposit side of a first home purchase, see our guide to how much deposit you need for a first home in Australia.