When people ask us how much they can borrow, most of them are thinking about one number: the interest rate on offer. It makes sense. It’s the number the bank advertises, the number that shows up in every headline, and the number everyone assumes decides what they can afford.
It’s not the number that decides your approval.
There’s another figure working quietly in the background of every home loan assessment, and most borrowers have never heard of it. It’s called the serviceability buffer, and it can matter more to your outcome than whatever the RBA does on any given Tuesday.
What Is the Serviceability Buffer?
The serviceability buffer is a safety margin that APRA (the Australian Prudential Regulation Authority) requires every lender to build into their assessment.
Instead of testing whether you can afford your loan at the rate you’ll actually pay, lenders have to test whether you could still afford it at your rate plus 3 percentage points.
So if you’re being offered a rate of 6%, the bank isn’t asking “can this person afford repayments at 6%?” It’s asking “can this person afford repayments at around 9%?”
That 3 percentage point margin has been in place since October 2021, and APRA reaffirmed it as recently as May 2026.
Why Does the Buffer Exist?
It’s not there to make borrowing harder for the sake of it. It’s a safety net.
Rates move. Circumstances change. Someone’s income can dip, a fixed rate can end and revert higher, life happens. The buffer exists so that when you’re approved for a loan, you’re not approved right on the edge of what you can afford, with no room to absorb a change later.
It’s a sensible idea in principle. The part that catches people out isn’t the buffer itself, it’s simply not knowing it’s there.
What This Looks Like in Practice
Take a $700,000 loan at a 6% interest rate.
At 6%, the repayments on a 30-year principal and interest loan come to roughly $4,196 a month.
Assessed at 9% (6% plus the 3 percentage point buffer), the bank is checking whether you could still manage repayments of roughly $5,632 a month, even though that’s not the amount you’ll actually pay.
That’s a meaningful gap, and it’s the reason two borrowers on identical incomes can walk away with two very different answers from the same lender. Existing debts, other credit limits and how your income is structured all interact with that buffer to shape your final number.
Why This Matters More Than the RBA, Some of the Time
When the RBA holds or moves the cash rate, it makes headlines. And it does matter, particularly for what you’ll actually pay each month.
But for the question of whether you get approved in the first place, the buffer is often doing more of the work. A rate rise or fall of 0.25% is a small shift against a 3 percentage point buffer that’s already built into every assessment, rate cycle or not.
If your borrowing power has come back lower than you expected, this buffer is one of the most common reasons why, and it has nothing to do with your income being too low or your situation being a poor fit for lending.
It’s Not Just the Buffer
The serviceability buffer is one part of the picture, not the whole thing. Credit limits you’re not using, existing debts, and how your income is documented can all move your number as well. We’ll be unpacking a few of those in the weeks ahead.
Final Thoughts
Most people focus on chasing the lowest advertised rate, and it’s an understandable place to start. But the number that actually decides what you’re approved for sits a full 3 percentage points above it.
Understanding that upfront means fewer surprises, and a much clearer picture of what you can genuinely afford before you start looking.
Want to Know Your Real Number?
If you’d like to understand exactly what you’d be assessed at, and what that means for your borrowing power, get in touch. We’ll walk you through it clearly, no jargon, no surprises.
