Mortgage offset account calculator
How much interest and time a savings balance in an offset account saves on a home loan.
Assumes you keep the same repayment, the offset balance stays steady and the rate does not change. Once the loan balance falls to your offset balance, no more interest is charged, but the loan is only fully repaid when the last repayments clear what is left. It ignores any package fee for the offset account.
How this calculator works
With an offset account you pay interest only on the loan balance minus the offset balance. Keeping the repayment the same means more of each payment goes to principal. The calculator simulates the loan month by month: interest = (balance − offset) × monthly rate, and the rest of the repayment reduces the balance. Interest stops once the balance falls to the offset balance, and the loan is fully repaid a little later.
Worked example: a $600,000 loan at 6.2% over 30 years has a repayment of $3,675 a month and costs $722,933 in interest. With $50,000 sitting in an offset the whole time, interest falls to $508,260, a saving of $214,673. The balance reaches $50,000 after 24 years, when interest stops, and the last repayments clear the loan after 25 years 2 months.
Sources and checks
You can cross-check results with:
Results can differ slightly from other tools because of rounding, fees and the assumptions each one makes.
Assumes a steady offset balance and a fixed rate.
Figures last checked: 29 October 2026. Spotted a mistake? Tell us.