How Australian Mortgage Payments Are Calculated

Summary

The Australian mortgage calculator computes monthly repayments using the standard amortization formula. The average owner-occupier variable rate is approximately 5.97% (February 2026, RBA data), and the national median dwelling price is around A$1,045,400 (CoreLogic). Most Australian home loans have a maximum term of 30 years.

How it works

Australian mortgages (commonly called “home loans”) differ from other markets in several ways:

• Variable rates dominate. Unlike the UK where 2-5 year fixed rates are standard, Australian borrowers frequently choose variable rate loans, though fixed-rate periods of 1-5 years are also available.
• APRA serviceability buffer. The Australian Prudential Regulation Authority (APRA) requires lenders to assess borrowers at a rate 3 percentage points above the loan product rate (or a floor of at least 5.5%, whichever is higher). This means a borrower applying at 5.97% must demonstrate they can service repayments at 8.97%.
• Lenders Mortgage Insurance (LMI). Borrowers with less than a 20% deposit (i.e., LTV above 80%) are typically required to pay LMI, a one-off premium that protects the lender (not the borrower) against default. LMI can add A$5,000-A$40,000+ to the cost of buying, depending on the loan amount and LVR.
• Offset accounts. Many Australian variable loans offer offset accounts, where the balance in a linked transaction account reduces the principal on which interest is calculated.
• First Home Owner Grant (FHOG). State and territory governments offer grants of A$10,000-A$30,000 for eligible first home buyers purchasing new homes below a price cap.

The repayment formula is: M = P x [r(1 + r)^n] / [(1 + r)^n - 1]

Where P is the loan principal, r is the monthly interest rate (annual rate / 12), and n is the total number of monthly payments (term x 12).

Worked example

A$800,000 property, 20% deposit (A$160,000), 5.97% variable rate, 30-year term:

1. Loan amount: A$800,000 - A$160,000 = A$640,000
2. Monthly rate: 5.97% / 12 = 0.4975%
3. Total payments: 30 x 12 = 360 months
4. Monthly repayment: A$640,000 x [0.004975 x (1.004975)^360] / [(1.004975)^360 - 1] = A$3,818/month
5. Total repayable: A$3,818 x 360 = A$1,374,480
6. Total interest: A$1,374,480 - A$640,000 = A$734,480

If the deposit were only 10% (A$80,000), the borrower would also need to pay LMI on the A$720,000 loan, adding an estimated A$15,000-A$25,000 to upfront costs.

Key differences from other markets

• No stamp duty exemptions nationally — stamp duty (called “transfer duty”) varies by state and territory, with first home buyer concessions differing in each jurisdiction, unlike the UK’s single SDLT system.
• Redraw facilities and offset accounts are standard features of Australian variable-rate loans, giving borrowers flexibility that is less common in the UK or US fixed-rate mortgage markets.