Free Australian mortgage repayment calculator. Enter your loan amount, interest rate, and loan term to instantly see repayment amounts for monthly, fortnightly, or weekly frequencies. Compare principal & interest vs interest-only repayments and view total interest payable over the life of the loan.
Monthly Repayment
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Total Interest
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Total Loan Cost
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Your mortgage repayment amount depends on three main factors: the loan amount (principal), the interest rate, and the loan term. Most Australian home loans are structured as principal and interest (P&I), meaning each repayment reduces both the interest owed and the outstanding loan balance.
Australian lenders work out a principal-and-interest repayment with the standard amortisation formula:
Repayment = P × r × (1 + r)n ÷ ((1 + r)n − 1)
where P is the loan amount, r is the interest rate per repayment period (the annual rate divided by the number of repayments a year), and n is the total number of repayments (loan term in years × repayments per year).
For a $500,000 loan at 6.19% p.a. over 30 years, paid monthly: the monthly rate is r = 6.19% ÷ 12 = 0.00515833, and the number of repayments is n = 30 × 12 = 360. Putting those into the formula gives a monthly repayment of about $3,059. Over the full term you would repay roughly $1,101,000 — meaning about $601,000 in interest on top of the $500,000 borrowed. Lower the rate or shorten the term and both the repayment and the total interest fall. (These figures are an illustration only; enter your own numbers in the calculator above.)
Switching from monthly to fortnightly repayments is one of the simplest ways to pay off your mortgage faster. Because there are 26 fortnights in a year, you effectively make 13 monthly payments instead of 12. This extra payment goes straight to reducing your principal, which can save tens of thousands of dollars in interest over the life of a 30-year loan.
Interest-only loans have lower initial repayments because you're not paying down the principal. They're commonly used by property investors for tax purposes. However, you'll pay significantly more interest over the life of the loan, and your repayments will jump when the interest-only period ends (typically after 1-5 years).
Use the principal-and-interest amortisation formula: Repayment = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan amount, r is the interest rate per repayment period (annual rate ÷ repayments per year), and n is the total number of repayments (years × repayments per year). For a $500,000 loan at 6.19% p.a. over 30 years paid monthly, that works out to about $3,059 a month. Each P&I repayment covers the interest charged plus a slice of the principal — early repayments are mostly interest, shifting toward principal over time.
It depends on how your lender calculates the fortnightly amount. If they set fortnightly to half of your monthly repayment, you effectively make 26 half-payments per year — equivalent to 13 monthly payments — and the extra goes to principal, saving interest. But if your lender uses 'true fortnightly' (monthly × 12 ÷ 26), the totals are the same and there's no saving. Ask your lender which method they use, or round up your fortnightly amount manually.
Principal & Interest (P&I) repayments pay down the loan balance plus interest each period. Interest-only repayments only cover the interest charged — your loan balance stays the same. Interest-only periods are typically 1-5 years, after which the loan converts to P&I.
Interest rates vary by lender and product. As of 2024-25, competitive variable rates for owner-occupiers are around 5.9-6.5% p.a. Fixed rates depend on the term. Compare rates from multiple lenders and consider the comparison rate, which includes fees.
Even small extra repayments can significantly reduce your loan term and total interest. For example, paying an extra $100/month on a $500,000 loan at 6% could save over $50,000 in interest and cut years off your mortgage. Check your loan for any restrictions on extra repayments.
Sources & methodology
This calculator applies the standard amortisation formula to the loan amount, interest rate, and term you enter, deriving the principal-and-interest repayment per period for your chosen frequency (monthly, fortnightly, or weekly) or, for interest-only, just the interest charged each period. It uses the rate you supply rather than a fixed FY 2025-26 rate, and all figures are computed in your browser — nothing you enter is stored or sent to a server.
Authoritative sources
Reviewed by Bishal Shrestha — Founder of OneBookPlus, 10+ years building tools with Australian tax-agent and BAS-agent practices. Last reviewed and updated: May 2026.
Disclaimer: This calculator produces estimates only and is not tax advice. Tax outcomes depend on your individual circumstances. For decisions that affect your tax position, consult a registered tax agent or the ATO directly.
OneBookPlus handles invoicing, GST tracking, BAS prep, and ATO lodgement automatically.
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