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calculateTool Usage Guide9 min readUpdated February 2026

How to Calculate Mortgage Repayments in Australia (Step-by-Step Guide)

A practical guide to calculating home loan repayments, understanding loan schedules, and testing interest rate scenarios.

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Overview & Purpose

Understanding how your mortgage repayments are calculated gives you total control over your home loan budget. This guide breaks down the exact formulas used by Australian banks, walks through step-by-step calculations, and demonstrates how changing repayment frequency or adding extra payments reduces interest.

Methodology

Step-by-Step Usage Instructions

1

Enter Your Total Loan Amount (Principal)

Input the exact amount you plan to borrow from the bank. Exclude your cash deposit, but include any capitalized fees like Lenders Mortgage Insurance (LMI) if applicable.

lightbulbPro Tip: If buying a $700,000 home with a 10% deposit ($70,000), your base loan principal is $630,000.
2

Select Your Loan Term (e.g. 25 or 30 Years)

Choose your desired loan length. Standard Australian home loans are structured over 30 years, but opting for 25 or 20 years significantly reduces overall interest paid.

lightbulbPro Tip: A 25-year term increases monthly payments slightly compared to 30 years, but saves tens of thousands in interest.
3

Input Your Variable or Fixed Interest Rate

Enter the annual comparison interest rate offered by your lender (e.g. 6.15% p.a.).

lightbulbPro Tip: Always check comparison rates, which include standard annual loan account fees.
4

Choose Repayment Frequency (Monthly, Fortnightly, Weekly)

Select how often payments will be deducted. Selecting fortnightly or weekly payments aligns with regular pay cycles and reduces total interest accrual.

lightbulbPro Tip: True fortnightly repayments (half the monthly amount every two weeks) pay off one full extra month of principal each year.

Ready to perform your calculations?

Input your numbers into our live interactive tool for real-time calculations and breakdown charts.

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Real Example

Worked Numerical Example

Example 1: $600,000 Loan at 6.25% over 30 Years (Monthly vs Fortnightly)

Comparing monthly payments vs true fortnightly payments on a standard $600,000 Australian mortgage.

Inputs Used
Loan Principal:$600,000
Interest Rate:6.25% p.a.
Loan Term:30 Years
Calculated Outputs
Monthly Payment:$3,694 / month
Fortnightly Payment (True):$1,847 / fortnight
Total Interest (Monthly):$730,008
Total Interest (Fortnightly):$586,120
Net Interest Saved:$143,888
Time Saved:4 Years 11 Months

Key Takeaway: Paying half the monthly repayment every two weeks results in 26 half-payments = 13 monthly payments per year, cutting nearly 5 years off the loan term.

Example 2: Impact of a 0.50% Interest Rate Increase on $750,000 Loan

Stress-testing a $750,000 home loan against a potential 50 basis point interest rate hike.

Inputs Used
Loan Principal:$750,000
Current Rate:5.90% p.a.
Increased Rate (+0.50%):6.40% p.a.
Calculated Outputs
Current Monthly Repayment:$4,449 / month
New Monthly Repayment:$4,691 / month
Monthly Repayment Increase:+$242 / month
Annual Increase:+$2,904 / year

Key Takeaway: A 0.50% rate rise adds $242/month to a $750,000 mortgage. Testing buffer scenarios helps ensure long-term budget stability.

How to Calculate Mortgage Repayments in Australia (Step-by-Step Guide) – FAQs

Answers to common questions about this calculation methodology.

Parent Knowledge Hub

Mortgages & Home Loans in Australia: The Complete Guide 2026–2027

Everything you need to know about borrowing power, interest rates, offsets, LMI, and paying off your home loan faster.

Read Full Pillar Guide
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