Extra Mortgage Repayment & Offset Calculator (Australia)
See how much interest and time you save by paying extra each month or keeping savings in a 100% offset account. It runs in your browser, and nothing you enter is sent anywhere.
Last updated 29 Oct 2026Figures for 2026-27Sources: ATO, SRO Victoria, ASIC Moneysmart
Your results
- Interest saved
- Time saved
- Scheduled repayment / month
- New payoff time
- Total interest, no extras
- Total interest with extras/offset
Not financial or tax advice. This is a general estimate from the figures you enter. It does not consider your personal circumstances. Check with a registered tax agent or licensed adviser before acting.
How it's calculated
- Scheduled repayment = standard principal and interest formula on the balance, rate and term, with monthly compounding.
- Each month, interest = (balance − offset, minimum $0) × rate ÷ 12.
- Balance = balance + interest − (scheduled repayment + extra), repeated until the loan is paid off.
- Savings are compared with the same loan with no extras and no offset.
Worked example
$500,000 at 6% over 30 years costs $2,997.75 a month and about $579,191 in total interest. With $500,000 sitting in the offset, no interest is charged, and the repayments clear the loan in 167 months.
Sources & assumptions
- ASIC Moneysmart: Mortgage offset accounts.
- ASIC Moneysmart: Pay off your mortgage faster.
- This is a maths model with no regulated rates. It assumes a constant rate, a constant offset balance, a 100% offset and no fees.
Last checked 29 October 2026. General information, not advice. Talk to your lender or a licensed broker.
FAQ
How much does an offset account save?
Each dollar in a 100% offset reduces the balance that interest is charged on, so it saves interest at your loan rate, tax-free. At 6%, $50,000 in offset saves about $3,000 in the first year.
Is it better to make extra repayments or use an offset?
On the numbers they save the same interest. An offset keeps the money accessible. Extra repayments can sometimes only be withdrawn by redraw, which lenders can restrict. Investors should get tax advice, because the choice can affect deductibility.
Do extra repayments reduce my repayment amount?
Usually not. Most lenders keep your scheduled repayment the same, and you finish early. This calculator assumes that.
Are there limits on extra repayments?
Variable loans usually allow unlimited extra repayments. Fixed loans often cap them (for example $10,000 a year) and charge break costs. Check your loan terms.
Does this use my actual lender's method?
It uses monthly compounding and repayments, a common simplification. Lenders calculate interest daily and charge it monthly, so real results differ slightly.