A serviceability buffer is an additional margin applied to your actual loan rate when a lender assesses whether you can afford the repayments.
It is set by the Australian Prudential Regulation Authority (APRA) – the regulator responsible for supervising banks and lenders to keep the financial system stable. It applies to all new residential mortgage lending by APRA-regulated banks. As of August 2026, APRA has set the buffer at three percentage points, meaning a loan advertised at 6% is actually tested as though you were paying 9%.
It’s a hurdle every borrower has to clear before a loan is approved, and it’s one of the biggest reasons your borrowing capacity can feel smaller than your income suggests.
This article is general information only and does not constitute financial, legal or tax advice. We recommend seeking advice from a qualified accountant, solicitor and licensed financial adviser before making any decisions.
Why does the serviceability buffer exist?
The buffer exists to make sure borrowers can still afford their repayments if interest rates rise significantly after settlement, rather than lenders assessing affordability only against the rate on offer at the time.
APRA introduced the current three percentage point buffer in October 2021, raising it from 2.5 percentage points amid concerns about rising household debt and an increase in highly leveraged borrowing.
The serviceability buffer now sits alongside another APRA measure that can affect mortgage borrowers – the debt-to-income (DTI) lending limit introduced from 1 February 2026. This caps how much of each lender’s new mortgage lending can go to borrowers with total debt at six times their income or more. APRA set that limit at 20% of new lending, applied separately to owner-occupier and investor loans, after flagging a build-up in higher-risk lending, particularly to investors, as interest rates fell in 2025.
Importantly, a DTI of six or more doesn’t automatically mean your application will be declined. The rule limits how much high-DTI lending each bank can write, rather than imposing a six-times-income borrowing cap on every individual borrower.
New dwelling purchases and construction loans are exempt from the DTI limit, though not from the serviceability buffer itself.
How does the mortgage serviceability buffer actually work?
It’s a straightforward rule, but it has a real impact on what you can borrow. In simple terms, whatever interest rate you’re offered, the lender adds three percentage points and tests your ability to repay at that higher figure. Investment loan variable rates currently range from around 5.99% at the lower end to 6.7% or higher from some lenders, according to Canstar (rates as at 18 August 2026, subject to change).
So on a loan at 6.24%, for example, a lender would assess your capacity to repay as though the rate were 9.24%, not the rate you’d actually be paying.
For investment properties specifically, the buffer isn’t the only adjustment impacting your borrowing capacity. Most lenders won’t count the full rent a property earns toward what you can service. Instead, they typically reduce a property investor’s declared gross rental income by 20% to 30% to account for potential vacant periods, management fees and maintenance costs. This is a practice known as rental shading.
According to SQM Research, Melbourne’s median weekly rent for houses was $819.66 in mid-August 2026. On a property renting at that level, a lender might count anywhere from around $574 to $656 of it toward your servicing, depending on where they sit within that shading range.
The exact figure varies by lender, and some may shade further depending on the property or your circumstances, so borrowers should treat that range as indicative rather than fixed.
What does this mean for how much you can actually borrow?
Between the mortgage serviceability buffer and rental income shading, the gap between what you believe you can afford and what a lender will actually approve can be significant. The impact will depend on your income, expenses, existing debts, rental income and the lender’s own assessment methodology. This is why we recommend running your own numbers with the team at AXTON Finance rather than assuming a flat percentage applies to your situation.
The 2026 Federal Budget's negative gearing changes may add another consideration for investors from 1 July 2027. Some lenders currently recognise negative gearing tax benefits when assessing serviceability. For established properties purchased after 12 May 2026, the ability to deduct rental losses against salary and other non-property income will change from July 2027, which may affect how some lenders assess borrowing capacity. The treatment will depend on individual lender policy, so it is worth checking how your proposed lender will assess your position before you apply.
Working out your own borrowing capacity
Understanding the mortgage serviceability buffer, rental shading and DTI rules can help explain why the amount a lender will actually approve may be very different from the number you arrive at using a basic mortgage calculator. A pre-approval based on your specific income, debts and the lender’s current policy is more accurate than a general rule of thumb.
This article is general information only and does not constitute financial, legal or tax advice. We recommend seeking advice from a qualified accountant, solicitor and licensed financial adviser before making any decisions.
Ready to find out your actual borrowing capacity? Speak to the team at AXTON Finance. Call 03 9939 7576, email getabetterrate@axtonfinance.com.au or get in touch.
