How mortgage repayments are calculated
Checked 15 Oct 2026. Uses the same approach as Moneysmart's mortgage calculator, so you can cross-check a result there.
Repayments on a principal and interest loan are calculated with the standard amortisation formula: each repayment covers that period's interest and pays down some principal. Early on, most of each repayment is interest.
Monthly repayments over 30 years
| Loan | 5.5% p.a. | 6% p.a. | 6.5% p.a. |
|---|---|---|---|
| $400,000 | $2,271 | $2,398 | $2,528 |
| $500,000 | $2,839 | $2,998 | $3,160 |
| $600,000 | $3,407 | $3,597 | $3,792 |
| $750,000 | $4,258 | $4,497 | $4,741 |
| $1,000,000 | $5,678 | $5,996 | $6,321 |
Principal and interest, monthly repayments, constant rate, no fees.
Total interest over 30 years
| Loan | 5.5% p.a. | 6% p.a. | 6.5% p.a. |
|---|---|---|---|
| $500,000 | $522,020 | $579,191 | $637,722 |
| $600,000 | $626,424 | $695,029 | $765,267 |
| $750,000 | $783,030 | $868,786 | $956,584 |
Half a percentage point on a $600,000 loan is about $191 a month more at 6% than at 5.5% and $68,605 in interest over the life of the loan.
Extra repayments
Anything you pay above the minimum comes straight off the principal, so every later repayment has less interest in it. On a $600,000 loan at 6% over 30 years, an extra $200 a month saves $106,693 in interest and finishes the loan 3 years 11 months early. An extra $500 a month saves $212,713 and 7 years 11 months. Check your loan allows extra repayments: fixed-rate loans often cap them.
Interest-only loans
Interest-only repayments are the loan × the rate ÷ 12: $3,000 a month on $600,000 at 6%, against $3,597 for principal and interest. But you repay nothing off the loan. After 5 years interest-only, the full $600,000 has to be repaid over the remaining 25 years, at $3,866 a month, and total interest comes to $739,743 instead of $695,029.
Tip: paying fortnightly, half your monthly repayment every two weeks, means 26 half-payments a year: the equivalent of 13 monthly payments. That extra payment can cut years off a 30-year loan. This calculator shows the true fortnightly amount for the same term, so compare carefully.
General information only, not financial, tax or credit advice. Check your situation with the ATO, your state revenue office or a licensed adviser.
Mortgage repayment FAQs
What are the repayments on a $600,000 mortgage?
$3,597 a month at 6% p.a. over 30 years, or $1,659.50 a fortnight or $829.58 a week. At 5.5% it's $3,407 a month and at 6.5% it's $3,792.
What are the repayments on a $500,000 or $750,000 mortgage?
$2,998 a month on $500,000 and $4,497 on $750,000, at 6% over 30 years. At 5.5% they're $2,839 and $4,258; at 6.5%, $3,160 and $4,741.
How much interest will I pay over 30 years?
$695,029 on a $600,000 loan at 6% p.a. with monthly repayments, so you repay $1,295,029 in total. At 5.5% the interest is $626,424 and at 6.5% it's $765,267. In the first year, $35,800 of the $43,168 you repay is interest.
How much do extra repayments save?
$106,693 in interest and 3 years 11 months off a $600,000 loan at 6% over 30 years, if you pay an extra $200 a month from the start. An extra $100 a month saves $58,423 and 2 years 1 month.
How much are interest-only repayments?
$3,000 a month on $600,000 at 6% (loan × rate ÷ 12), against $3,597 for principal and interest. After 5 interest-only years the repayment jumps to $3,866 a month for the remaining 25 years, and you pay $44,713 more interest overall.
Does this include fees or LMI?
No. It covers principal and interest only, at a constant rate. Lender fees, lenders mortgage insurance and rate changes aren't included.
How much will I save with an offset account?
About $202,175 in interest and 4 years 8 months off the loan, with $50,000 in offset against a $600,000 loan at 6% over 30 years and the same $3,597 monthly repayment. Use the offset account calculator for your own balance.