Extra Mortgage Repayments Mistakes Australians Make and How to Avoid Them

Updated 15 July 2026 · Property and home loans

A Extra Mortgage Repayments Calculator gives a fast answer, but the answer is only as good as what goes in. These are the mistakes we see most often with extra mortgage repayments calculations in Australia, and how to avoid them.

1. Assuming prices always rise

Property growth varies by location and period. Plan for flat or falling prices too.

2. Borrowing the maximum

Lenders test you at a higher rate, but your budget still needs room for rate rises, repairs and life changes.

3. Forgetting purchase costs

Stamp duty, conveyancing, inspections and moving can add several percent to the price.

4. Comparing headline rates only

Fees, offset accounts and flexibility on extra repayments can matter as much as the rate.

5. Overlooking the detail that matters most here

Fixed-rate loans often limit extra repayments to $10,000–$20,000 a year. Check before paying more.

How the interest saved changes with interest rate

A common mistake is getting one input slightly wrong. Here is what happens to the interest saved when “Interest rate (%)” is off by up to 20% in either direction, with everything else held steady.

Interest rate (%)	Interest saved
5	$152,901.27
6	$199,501.27
7	$252,535.80

At 5 the result is $152,901.27; at 7 it is $252,535.80. If a small change in this input moves the answer a lot, it is worth double-checking that figure before you rely on the result.

A quick sense check

The loan is amortised month by month with and without the extra payment, and the interest totals are compared. With typical inputs the calculator returns interest saved of $199,501.27. If your own result looks wildly different, check that each figure is in the right unit and period (weekly, monthly or yearly) before drawing conclusions.