Everything You Need to Know About Interest Rates and Borrowing

How Interest Rates Reduce Borrowing Capacity

Lenders assess your ability to repay at a rate substantially higher than the advertised product rate. Under APRA requirements, all authorised deposit-taking institutions must test new borrowers at an interest rate at least 3.0 percentage points above the loan product rate. A buyer applying for a variable rate home loan at 6.2 per cent will be assessed at 9.2 per cent or higher. This buffer protects both lender and borrower against future rate rises, but it also reduces the loan amount you can access.

Consider a buyer in Truganina with a combined household income of $140,000 and monthly commitments of $1,800. At a product rate of 6.2 per cent, the monthly repayment on a $600,000 loan over 30 years would be approximately $3,670. Under the serviceability buffer, the lender calculates repayments at 9.2 per cent, which increases the tested monthly repayment to approximately $4,870. The lender then applies a net surplus ratio to ensure the household can meet all financial obligations and living expenses. In this scenario, the buyer may be approved for a loan closer to $540,000 rather than $600,000, depending on the lender's living expense benchmarks and the buyer's existing commitments.

The buffer is not applied to your actual repayments. You still pay the product rate. The higher rate is used only to calculate whether you can afford the loan if rates rise.

The Debt-to-Income Limit and Its Application

From 1 February 2026, APRA activated a debt-to-income lending limit applying to all authorised deposit-taking institutions. Each lender may approve up to 20 per cent of new owner-occupier loans and up to 20 per cent of new investor loans to borrowers with a total debt-to-income ratio of six times or greater. A household earning $140,000 would reach the six-times threshold at a total debt level of $840,000. A buyer in Truganina purchasing at the current median with a 10 per cent deposit and existing personal debts of $30,000 may fall within this threshold, depending on the purchase price and lender assessment.

The DTI limit does not prohibit lending above six times income. It constrains the proportion of high-DTI lending each institution can write in a given quarter. Borrowers with a DTI above six may still be approved, but lenders prioritise these approvals for applicants with strong financial profiles, stable employment, and minimal other liabilities. Bridging loans for owner-occupiers and loans for the purchase or construction of new dwellings are excluded from the DTI calculation.

Truganina's Housing Stock and Borrowing Context

Truganina sits within the City of Wyndham, approximately 22 kilometres west of Melbourne's central business district. The suburb has experienced rapid residential development over the past decade, with a high proportion of new and near-new homes. Many buyers in the area are first home buyers or families upgrading from established suburbs closer to the city. The prevalence of newer stock means many transactions align with state and federal concessions that favour new builds, including the Victorian First Home Owner Grant and the Australian Government 5% Deposit Scheme.

Buyers in Truganina typically require a home loan structure that balances serviceability with access to government support. A buyer purchasing a new home valued at $680,000 with a 5 per cent deposit would be assessed not only on the deposit and serviceability buffer, but also on whether the property value falls within the applicable caps for the 5% Deposit Scheme and the Victorian stamp duty concession. The property price cap for the 5% Deposit Scheme in Victoria is $950,000 in capital cities and regional centres, and $650,000 in other areas. Truganina, as part of metropolitan Melbourne, falls within the $950,000 cap. The Victorian stamp duty exemption applies to new and established homes valued up to $600,000, with a sliding concession for properties valued between $600,001 and $750,000.

Fixed, Variable, and Split Rate Structures

The choice between a fixed rate, variable rate, or split loan structure affects both your repayment amount and your borrowing capacity assessment. Lenders apply the serviceability buffer to the product rate you select. A buyer choosing a three-year fixed rate at 5.9 per cent will be assessed at 8.9 per cent or higher. A buyer choosing a variable rate at 6.2 per cent will be assessed at 9.2 per cent or higher. The difference in product rates can shift borrowing capacity by tens of thousands of dollars, even though the buffer percentage remains constant.

A split loan divides the borrowed amount into separate fixed and variable components. A buyer in Truganina might split $550,000 into $350,000 fixed and $200,000 variable. The fixed portion provides repayment certainty for the fixed term, while the variable portion allows for additional repayments and access to an offset account. Lenders assess each portion separately under the serviceability buffer, then aggregate the tested repayments to determine total serviceability. In our experience, buyers who expect income growth or who hold irregular income streams often favour a split structure because it combines stability with flexibility. Those considerations should be weighed alongside your borrowing capacity before you settle on a loan structure.

How Lenders Treat Existing Debts and Commitments

Lenders include all existing financial commitments when calculating your borrowing capacity. Personal loans, car loans, credit card limits, and buy-now-pay-later accounts are factored into your net surplus calculation. Even if a credit card has a zero balance, lenders typically assess it at the full credit limit, assuming you could draw the entire amount at any time. A buyer with a $15,000 credit card limit and a $25,000 car loan will see their borrowing capacity reduced by the amount required to service those commitments under the lender's assessment rate.

Consider a buyer in Truganina with a gross household income of $130,000, a $20,000 car loan with 24 months remaining, and two credit cards with combined limits of $18,000. The lender calculates the ongoing car loan repayment and applies a notional repayment of 3 to 4 per cent of the credit card limit per month, regardless of actual usage. In this scenario, the buyer's borrowing capacity might be reduced by $80,000 to $100,000 compared to a buyer with the same income and no existing debts. Paying down or closing unused credit accounts before applying for a home loan pre-approval can materially improve your borrowing position.

Owner-Occupied Versus Investment Loan Structures

Lenders apply different serviceability criteria and risk weights to owner-occupied loans and investment loans. An owner-occupied loan generally supports a higher borrowing capacity than an investment loan for the same applicant, due to lower risk weighting and favourable treatment of rental income in serviceability calculations. Where there is any doubt about whether a loan is for owner-occupied or investment purposes, APRA requires the loan to be treated as an investment loan under Prudential Standard APS 112.

For buyers in Truganina, the distinction is particularly relevant for those purchasing a new home while retaining an existing property. A buyer who intends to rent out their current residence and move into the new property must declare the new loan as owner-occupied and the existing loan as investment. The lender will reassess the borrowing capacity based on the rental income from the existing property, the existing loan repayments, and the new loan serviceability buffer. Rental income is typically assessed at 80 per cent of the actual or market rent to account for vacancy and maintenance costs. The combined effect can reduce the amount available for the new purchase, even though the buyer's overall equity position has improved.

Deposit Size, LMI, and Borrowing Capacity

The size of your deposit affects both the loan amount you require and whether you will pay lenders mortgage insurance. LMI applies to loans where the loan-to-value ratio exceeds 80 per cent. The premium is calculated on a sliding scale based on the loan amount and LVR, and is added to the loan balance or paid upfront. A buyer in Truganina purchasing a $650,000 property with a 10 per cent deposit would borrow $585,000, resulting in an LVR of 90 per cent. The LMI premium on a loan of this size and LVR may range from $15,000 to $25,000, depending on the lender and insurer.

LMI does not reduce your borrowing capacity directly, but it increases the total amount you need to borrow, which in turn increases your monthly repayments and may push you closer to your maximum serviceability threshold. A buyer approved for a $585,000 loan may find that adding $20,000 in LMI results in a total borrowing requirement of $605,000, which exceeds their assessed capacity. In that scenario, the buyer would need to increase their deposit, reduce the purchase price, or seek a co-borrower to meet the lender's serviceability requirements. The Australian Government 5% Deposit Scheme allows eligible first home buyers to avoid LMI by accessing a government guarantee, which can preserve borrowing capacity for buyers with smaller deposits.

When to Lock in Pre-Approval and How Rates Affect Timing

Pre-approval provides conditional loan approval based on your current financial position and the lender's assessment criteria at the time of application. Most lenders issue pre-approval with a validity period of 90 days, though some extend to 120 days. If interest rates rise during the pre-approval period, lenders may reassess your borrowing capacity before issuing formal approval. A buyer in Truganina who obtained pre-approval at a product rate of 6.0 per cent in June may find that a rate increase to 6.4 per cent in August reduces their approved loan amount by $20,000 to $30,000, even though the pre-approval remains technically valid.

Locking in pre-approval when rates are stable or declining can protect your borrowing capacity, but it also commits you to a purchase timeline. If you do not proceed to formal application within the validity period, you will need to reapply, and the lender will assess you under current rates and serviceability criteria. For buyers in growth areas like Truganina, where new estates are releasing in stages, timing your pre-approval to align with settlement dates is a matter of balancing rate protection against contract flexibility.

Call one of our team or book an appointment at a time that works for you. We work with buyers across Truganina and the western growth corridor, and we can provide a detailed serviceability assessment based on your income, commitments, and preferred loan structure.

Frequently Asked Questions