Mortgage repayment calculator
Work out the repayment on a home loan, how much of it is interest, and what paying a little extra each period actually saves you.
Monthly repayment
$3,938.97
54% of everything you repay is interest
- Total interest
- $768,025
- Total repaid
- $1,418,025
- Paid off in
- 30 years
| Amount borrowed | $650,000 |
|---|---|
| Interest | $768,025 |
| Total repaid | $1,418,025 |
On a 30-year loan at 6.1%, 54% of everything you repay is interest, and the first repayment alone is 84% interest.
Over the life of it
How this is calculated
The repayment formula
A standard amortising loan uses a level instalment sized so the balance reaches zero on the final payment. The periodic rate is the annual rate divided by the number of repayments a year.
payment = P · i / (1 − (1 + i)^−n)Extra repayments and the final instalment
Extra money goes entirely to principal, so it removes both the balance and every future interest charge on it — $200 a month here saves $111,136. The last instalment is trued up to the exact balance, which is why the schedule closes at zero rather than a few cents out.
Worked example: $650,000 over 30 years at 6.1%
| Amount borrowed | $650,000 |
|---|---|
| Rate | 6.10% p.a. |
| Term | 30 years, monthly |
| Monthly repayment | $3,939 |
|---|---|
| Total interest | $768,025 |
| Total repaid | $1,418,025 |
Adding $200 a month clears the loan 3.7 years early and saves $111,136 in interest — about 28 times the extra you put in.
What this assumes
- The rate never changes for the whole term.
- Repayments are made on time, every period.
- No fees, offset account, or redraw.
- No lender mortgage insurance or stamp duty.
Where this commonly goes wrong
- The advertised rate is not the comparison rate: fees can add 0.1–0.4 percentage points to the real cost.
- Fortnightly repayments only save money when they are half the monthly amount — that makes 26 half-payments, or 13 months of repayments a year.
- Extra repayments only shorten the loan if the lender applies them to principal immediately, rather than holding them as advance payments.
Questions
How much of my repayment goes to interest?
At the start, most of it. On a $650,000 loan at 6.1% the first monthly repayment is about $3,304 interest and $634 principal. The split reaches 50/50 at year 18.8, then flips quickly.
Do fortnightly repayments really pay off a loan faster?
Only if each one is exactly half the monthly repayment. That produces 26 half-payments a year — the equivalent of 13 monthly repayments instead of 12. If the lender simply recalculates a true fortnightly amount, the saving disappears.
Is it better to pay extra off the loan or invest?
Paying down a loan returns exactly the loan rate — 6.1% here — with no market risk and no tax on the saving. Investing might return more, with risk and tax attached. Compare the loan rate against your expected after-tax return, not the headline market return.
What happens to my repayment if rates rise 1%?
On a $650,000 loan over 30 years, a rise from 6.1% to 7.1% lifts the monthly repayment by $429. Enter the higher rate here to see your own figure before you borrow, not after.
Why does a Canadian lender quote a different repayment?
Canadian mortgage rates are quoted with semi-annual compounding by law, so the monthly periodic rate is (1 + r/2)^(1/6) − 1 rather than r/12. Switch the rate convention under More options to match.
Does this include property tax, insurance or strata?
No. This is principal and interest only. Ongoing costs such as council rates, insurance, strata and maintenance typically add 0.5–1.5% of the property value each year and are not part of the loan repayment.
Related tools
Sources
This calculator does arithmetic on the figures you enter. It does not account for tax, fees, or your personal circumstances.
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