Everything You Need to Know About Rates and Borrowing Power

A small shift in the interest rate on your home loan changes how much a lender will offer you, sometimes by tens of thousands of dollars.

Lenders assess your ability to repay at a rate higher than what you'll actually pay, and when rates move, that buffer changes the numbers behind the scenes. For buyers in Trigg, where proximity to the coast and family-friendly streets often mean price tags above the Perth metro median, understanding this relationship can mean the difference between securing the property you want and falling short at approval.

Why the Rate You're Quoted Isn't the Rate You're Assessed At

Lenders assess your capacity to service a loan at an interest rate 3.0 percentage points above the product rate you're applying for. This buffer has been in place since October 2021 and applies to all new borrowers through banks, credit unions and building societies regulated by APRA. If you're applying for a variable rate loan at 6.2%, the lender will assess whether you can afford repayments at 9.2%. If you're applying for a fixed rate at 5.8%, the assessment happens at 8.8%.

Consider a buyer looking at a property near the Trigg foreshore. They're applying for a loan of $700,000 on a 30-year term. At a product rate of 6.2%, monthly repayments sit around $4,290. At the serviceability buffer rate of 9.2%, repayments jump to around $5,650. The lender will use the higher figure to work out whether your income can support the loan, even though you'll only be paying the lower amount each month.

This buffer exists to protect borrowers from interest rate increases over the life of the loan. If rates rise after you settle, you're less likely to fall into financial hardship because you've already been assessed at a higher rate.

How Rate Increases Reduce What You Can Borrow

When the product rate rises, the buffer rate rises with it. A lender assessing your income at a higher serviceability rate will calculate a lower maximum loan amount. This happens before you even see a formal offer.

In our experience, a 0.5% increase in the product rate can reduce borrowing capacity by around $30,000 to $50,000 for a household earning $120,000 a year, depending on existing debts and living expenses. The exact figure varies by lender, but the direction is consistent. Higher rates mean smaller loans.

For Trigg buyers, where the median house price sits well above entry-level suburbs further inland, a reduction of $40,000 in borrowing capacity can shift your search from a renovated three-bedroom cottage to a property that needs work, or from a home within walking distance of the beach to one several streets back.

Fixed Versus Variable Rates and How Lenders Treat Each

The serviceability buffer applies to both fixed and variable products, but the rate you're assessed at depends on the product you choose. Lenders typically assess fixed rate applications using the fixed rate plus the buffer, and variable rate applications using the variable rate plus the buffer. If you're applying for a split loan, where part of the balance is fixed and part is variable, the lender will assess each portion separately and combine the results.

Some lenders apply additional overlays to their serviceability calculations. These are internal credit policies that sit on top of the regulatory buffer. For example, a lender might assess interest-only applications at a higher rate or reduce the maximum loan amount for borrowers with multiple debts. These overlays aren't advertised and vary between institutions.

Debt-to-Income Limits Add Another Layer

From 1 February 2026, banks and other ADIs have been required to limit the proportion of new loans they write to borrowers with a debt-to-income ratio of six times or more. Each lender can write up to 20% of new owner-occupier loans and 20% of new investor loans to borrowers above this threshold.

If your total borrowing, including the new loan, is more than six times your gross annual income, you may be placed in that 20% bucket. If the lender has already filled its quota for the quarter, your application may be declined or deferred, even if you meet all other serviceability criteria.

As an example, a household earning $150,000 a year applying for a loan of $950,000 would sit at a DTI ratio of just over 6.3. Depending on the lender's position in the quarter, that application might be approved, or it might be pushed back until the next reporting period.

What Happens to Your Borrowing Power When You Refinance

If you're refinancing an existing loan, the same serviceability rules apply. Lenders assess your income and expenses as if you were a new borrower, which means the 3.0 percentage point buffer is applied to the new product rate.

This can create a situation where you're unable to refinance the full amount of your existing loan if rates have risen since you first borrowed. In that case, you may need to reduce the loan amount by making a lump sum payment, or you may need to stay with your current lender and negotiate a retention rate instead.

We regularly see this with clients coming off fixed rates that were locked in during the low-rate period. The loan amount that was approved at 2.5% with a buffer of 5.5% may not be approved at a product rate of 6.5% with a buffer of 9.5%, particularly if income hasn't increased in the interim.

How Offset Accounts and Loan Features Interact with Capacity

The features attached to your loan don't directly change your borrowing capacity, but they can influence the rate you're offered, which in turn affects the serviceability calculation. A loan with an offset account, redraw facility and portability will often carry a slightly higher rate than a no-frills package, particularly if you're borrowing at a high LVR.

For Trigg buyers looking at properties in the $900,000 to $1,200,000 range, the difference between a basic variable rate and a package rate with full features might be 0.15% to 0.25%. That difference flows through to the buffer rate and can reduce borrowing capacity by $10,000 to $20,000.

If you're choosing between a loan with features and a cheaper rate, run the numbers on how much you can borrow under each scenario before deciding. A slightly lower rate might get you across the line on a property you otherwise couldn't afford, but it may also mean giving up flexibility you'll want later.

Call one of our team or book an appointment at a time that works for you. We'll walk through your income, expenses and deposit, show you what different rates mean for your borrowing capacity, and structure a loan that fits the property you're targeting in Trigg or nearby suburbs.

Frequently Asked Questions