In short: This calculator shows what a home loan costs each month, fortnight or week for a given loan amount, interest rate and term. A useful rule of thumb at today's rates: every $100,000 you borrow over 30 years costs roughly $600 a month at 6.00% p.a., so a $650,000 Melbourne loan lands near $3,900 a month.
- Total interest over the loan$695,029
- Total repaid$1,295,029
- Loan term30 years
Assumes the rate stays the same for the whole term. Your lender may round repayments. Comparison rates, fees and LMI are excluded.
Repayment per month: $3,597.30
That is a general estimate on standard assumptions. Every lender applies its own expense benchmarks, income shading and policy, so the real figure moves from lender to lender. Gorakh spent years as a senior credit officer deciding exactly these questions. Send him the numbers above and he will tell you what is realistic and which lenders fit — at no cost to you for home loans.
- A former senior credit officer reads itGorakh assessed loan applications on the lender side before he became a broker.
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Repayments decide whether a property is comfortable or a stretch, so it pays to know what moves the figure.
How this calculator works
The tool uses the standard amortisation formula every Australian lender uses for principal-and-interest loans. Your monthly repayment equals the loan amount multiplied by the monthly rate (annual rate divided by 12), divided by one minus (1 plus the monthly rate) raised to the power of negative the number of months. In plain English: it finds the fixed payment that clears the whole balance, plus interest charged on the shrinking balance, by the end of the term.
Assumptions built in
- Interest is charged monthly on the daily balance, as most lenders do.
- The rate stays the same for the whole term, so treat the result as a snapshot.
- Fortnightly figures are half the monthly repayment and weekly a quarter, which quietly adds one extra monthly repayment a year.
- Interest-only repayments are the balance multiplied by the annual rate, divided by 12.
How to use the result
Compare the repayment with your take-home pay. Lenders generally get uncomfortable when a loan absorbs more than about 30% of gross household income, and you should test what happens if the rate rises by 3 percentage points, which is exactly what the lender does under the APRA serviceability buffer. If the buffered repayment still leaves room for living costs and childcare, the loan is sustainable. If not, lower the price or grow the deposit before you apply for pre-approval.
Worked example
A couple buying a $780,000 house in Craigieburn with a 20% deposit borrows $650,000 (for illustration, at 6.00% p.a.):
| Loan and term | Monthly repayment | Total interest over term |
|---|---|---|
| $650,000 over 30 years, P&I | $3,897 | $752,948 |
| $650,000 over 25 years, P&I | $4,188 | $606,400 |
| $650,000 interest-only | $3,250 | Balance never falls |
| $650,000 at 5.50% p.a., 30 years | $3,691 | $678,760 |
| $650,000 at 6.50% p.a., 30 years | $4,108 | $828,880 |
Shortening the term to 25 years adds about $291 a month but saves close to $147,000 in interest. And half a percent of rate is worth around $200 a month, which is why comparing lenders matters.
What this calculator doesn't include
- Ongoing fees such as annual package or account fees, which the comparison rate captures and the headline rate does not.
- Rate changes after a fixed period ends, or the revert rate on an introductory offer.
- The effect of an offset account or redraw, which can reduce interest without changing the scheduled repayment.
- Upfront costs like stamp duty, LMI and conveyancing. Use the upfront costs calculator for those.
- Council rates, insurance and maintenance.
Tips to improve the outcome
- Pay fortnightly rather than monthly. Half the monthly amount every two weeks means 26 payments a year, equal to 13 monthly repayments instead of 12.
- Round your repayment up. Adding even $100 a month to the $650,000 example clears the loan two years early; see the extra repayments calculator.
- Review your rate every 12 to 18 months. If your lender won't match the market, refinancing is often straightforward.
- Consider a fixed and variable split for certainty plus flexibility; the split loan calculator shows the combined repayment.
Frequently asked questions
How much are the repayments on a $600,000 mortgage?
At 6.00% p.a. over 30 years, a $600,000 principal-and-interest loan costs about $3,597 a month, or roughly $1,799 a fortnight. Over 25 years it rises to around $3,866. Interest-only repayments would be $3,000 a month, but the debt would not reduce.
What is the formula for mortgage repayments in Australia?
Australian lenders use the standard amortisation formula: repayment = P × r ÷ (1 − (1 + r)^−n), where P is the loan amount, r is the annual rate divided by 12 and n is the number of monthly repayments. For a $500,000 loan at 6.00% over 30 years, r is 0.005 and n is 360, giving $2,998 a month.
Is it better to pay a mortgage weekly, fortnightly or monthly?
Fortnightly or weekly repayments help only if the lender calculates them as half or a quarter of the monthly amount. That structure delivers one extra monthly repayment every year, which on a $650,000 loan at 6.00% cuts around five years and roughly $160,000 of interest from a 30-year term. If the lender simply divides the annual total by 26, there is no advantage.
How much do repayments change if interest rates rise by 1%?
For every 1 percentage point rise, repayments on a 30-year loan increase by roughly $65 a month per $100,000 borrowed. On $650,000 that is about $420 a month, taking the repayment from $3,897 at 6.00% to around $4,320 at 7.00%. Lenders already stress-test you for a 3 percentage point rise, so a comfortable approval has room for this.
Does a longer loan term reduce my repayments?
Yes, but at a cost. Stretching $650,000 from 25 to 30 years lowers the monthly repayment by about $291, yet adds close to $147,000 in extra interest over the life of the loan. Many borrowers take the 30-year term for flexibility and make voluntary extra repayments, getting the lower minimum with the interest savings of a shorter term.
Talk to GNT Finance
Repayment estimates are only as good as the rate behind them. GNT Finance compares home loans from dozens of lenders and structures the loan so the repayment fits your budget, at no cost to you for our home-loan service in most cases. Book a free consultation or call Gorakh Timilsina on 0426 403 703.
Written by Gorakh Timilsina
Founder, CEO & Senior Mortgage Consultant at GNT Finance. Gorakh started as a broker assistant, spent years as a senior credit officer assessing loan applications, and now helps Melbourne families get the right loan approved. English, Nepali and Hindi spoken.