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Mortgage repayment calculator
On a $650,000 loan at 6.49% over 30 years, repayments are $4,104.17 a month. Over the full term you would pay $827,499 in interest — more than the amount borrowed. Change the figures below.
Repayment
$4,104.17
per month
| Loan amount | $650,000.00 |
|---|---|
| Total interest | $827,499.38 |
| Total repaid | $1,477,499.38 |
| Time to repay | 30 years |
Repayment as the rate moves
Of $1,477,499 total repaid, Principal (what you borrowed) 44.0%, Interest 56.0%.
- Principal (what you borrowed) 44.0%
- Interest 56.0%
What you still owe, year by year
Each line stops where that loan is paid off, so the gap between the ends is the time you save. Change the loan, the offset or the extra repayment above and all three move.
- As entered
- With $500 extra a month
- With $50,000 in offset
As entered
With $500 extra a month
With $50,000 in offset
Balance remaining on a $650,000 loan, year by year. As entered: paid off after 30 years, $827,499 of interest. With $500 extra a month: paid off after 22.33 years, $580,848 of interest. With $50,000 in offset: paid off after 25.25 years, $589,907 of interest.
Saves $246,651 in interest and 7.7 years.
Saves $237,593 in interest and 4.8 years.
What an offset account actually does
An offset account reduces the balance interest is charged on, but not the balance you owe. Your repayment stays the same, so more of each one goes to principal and the loan finishes early. That is why the saving is far larger than the interest on the offset balance alone.
| Scenario | Term | Total interest | Saved |
|---|---|---|---|
| No offset, no extra | 30 yrs | $827,499 | — |
| $50,000 in offset | 25.25 yrs | $589,907 | $237,593 |
| $500 extra per month | 22.33 yrs | $580,848 | $246,651 |
The fortnightly trick, explained honestly
"Switch to fortnightly and save years" is usually true, but not for the reason people think. It depends entirely on which convention your lender uses:
| Convention | Per fortnight | Paid per year |
|---|---|---|
| True fortnightly rate (r ÷ 26) | $1,893.34 | $49,227 |
| Half the monthly repayment | $2,052.09 | $53,354 |
Paying half the monthly amount 26 times means you pay 13 monthly repayments a year, not 12. The saving comes from paying roughly $4,104 more each year, not from the frequency itself. Our calculator above uses the true periodic rate.
If your loan is interest-only
Interest-only repayments on this loan would be $3,515.42 a month. When a 5-year interest-only period ends, the loan re-amortises over the remaining 25 years, so repayments jump to $4,384.79 — a step-up of $869.37 a month. That jump is what catches people out.
Assumptions and limitations
- Interest accrues daily on a 365-day year and is charged each period, which is standard Australian practice. Your lender's exact day count may differ.
- The rate is assumed constant for the whole term. It will not be. The Reserve Bank has moved the cash rate 4 times in 2026 alone, to 4.60%. The default rate is the average owner-occupier variable rate after that rise (Canstar). See where it could go next with the RBA rate forecast model.
- With rate changes switched on, each change re-sets the minimum repayment so the loan still ends on the original date, which is how variable loans work. If you keep paying the old, higher amount after a cut, you finish sooner.
- Offset balances are held flat for the projection. In reality they fluctuate.
- Fees, lender's mortgage insurance and government charges are excluded.
- This is a model, not a prediction, and not a loan offer.
Estimate only, not financial advice. This calculator is not intended to be relied on for the purposes of making a decision in relation to a financial product; consider obtaining advice from a licensed financial services provider. See our methodology.