Enter your loan amount, interest rate and term to calculate your monthly payment, total interest and total cost of the mortgage instantly. Free, no signup required.
The amount you are borrowing — your purchase price minus your down payment. If you are buying a $400,000 property with a $80,000 down payment (20%), enter $320,000. The loan amount is the figure on which all interest is calculated. Every $10,000 reduction in loan amount reduces your monthly payment and saves thousands in interest over the loan’s life.
The yearly interest rate your lender charges on the outstanding balance. Enter the rate exactly as quoted in your mortgage offer — this is typically the nominal rate, not the APR. Even a 0.5% difference in rate has a material impact over a 25 or 30 year term. On a $300,000 loan at 30 years, the difference between 6.0% and 6.5% is approximately $97 per month and over $34,000 in total interest.
The number of years over which you repay the mortgage. Common terms are 15, 20, 25 and 30 years. A shorter term means higher monthly payments but substantially lower total interest. A longer term lowers the monthly payment at the cost of paying interest for more years. Run the calculator at two different terms to see the exact trade-off in your specific scenario.
Monthly Payment: The fixed amount you pay each month, covering both principal repayment and interest. This figure does not include property taxes, buildings insurance or any mortgage protection insurance — your actual housing cost will be higher than this figure.
Total Interest: The total amount of interest you will pay over the full loan term if you make every scheduled payment and never overpay or refinance. This number is often surprising — on a 30-year mortgage at typical rates, total interest frequently exceeds the original loan amount.
Total Cost: Your loan amount plus total interest — the full amount you will have paid by the time the mortgage is cleared.
A buyer takes out a $320,000 mortgage at 6.5% over 30 years.
| Monthly payment | $2,023 |
| Total interest | $408,280 |
| Total cost | $728,280 |
The buyer borrows $320,000 and pays back $728,280 over 30 years. The interest alone — $408,280 — is 127% of the original loan.
Now compare the same loan over 20 years:
| 30-year term | 20-year term | |
|---|---|---|
| Monthly payment | $2,023 | $2,390 |
| Total interest | $408,280 | $253,600 |
| Total cost | $728,280 | $573,600 |
| Monthly difference | — | +$367 |
| Interest saved | — | $154,680 |
Paying $367 more per month saves $154,680 in interest and eliminates the mortgage 10 years earlier. The calculator makes this comparison immediate — run your specific numbers in both fields before committing to a term.
The calculator uses the standard mortgage amortisation formula:
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
Where:
For the example above: P = $320,000, annual rate = 6.5%, r = 6.5% / 12 = 0.5417%, n = 360 months.
M = $320,000 × [0.005417 × (1.005417)³⁶⁰] / [(1.005417)³⁶⁰ − 1] M = $2,023
The monthly payment is fixed for the entire term on a fixed-rate mortgage. What changes each month is the split between interest and principal — this is the amortisation schedule.
Every monthly payment covers two components: interest on the outstanding balance and a reduction of the principal. The critical point most borrowers miss is that this split changes dramatically over the loan’s life.
In the early years, the vast majority of each payment goes to interest. As the balance falls, progressively more of each payment reduces the principal.
For the $320,000 loan at 6.5% over 30 years:
| Year | Interest paid | Principal paid | Balance remaining |
|---|---|---|---|
| 1 | $20,640 | $3,636 | $316,364 |
| 5 | $20,173 | $4,103 | $301,412 |
| 10 | $19,364 | $4,912 | $284,247 |
| 15 | $18,157 | $6,119 | $260,879 |
| 20 | $16,328 | $7,948 | $227,091 |
| 25 | $13,430 | $10,846 | $176,038 |
| 30 | $8,609 | $15,667 | $0 |
After 10 full years of payments, the borrower has paid $142,760 in total — but the mortgage balance has only fallen from $320,000 to $284,247. Only $35,753 of principal has been repaid in a decade of payments.
This is why making overpayments in the early years of a mortgage has a disproportionate impact — every pound or dollar of principal repaid early eliminates years of future interest on that amount.
Enter your remaining mortgage balance as the loan amount, the new interest rate you have been offered, and your desired new term. The calculator shows your new monthly payment and new total interest. Compare this against your current remaining payments to assess whether refinancing saves money overall.
Note: refinancing typically involves arrangement fees, valuation costs and legal fees. Always deduct the full refinancing cost from the interest saving to assess the true net benefit before proceeding.
No. The monthly payment shown covers principal and interest only. Property taxes, buildings insurance, contents insurance and mortgage protection insurance are separate costs that vary by location and individual circumstances. Add these to the monthly figure to get your true total housing cost.
This calculator assumes a repayment mortgage where each payment reduces the outstanding balance. For an interest-only mortgage, the monthly payment is simply: Loan Amount × (Annual Rate / 12). On a $300,000 interest-only mortgage at 6.5%, the monthly payment is $1,625 — but the balance remains at $300,000 until a lump sum repayment is made at the end of the term.
Enter the loan amount after and down payment — not the purchase price. A larger down payment reduces the principal, which lowers both your monthly payment and total interest. It may also reduce your interest rate if a larger deposit moves you into a more favourable loan-to-value band.
Use the rate quoted in your mortgage offer or indicative quote — typically the annual nominal rate. If you have only been given an APR, use that figure. For comparison purposes, you can run the calculator at several different rates to see how sensitive your payment is to rate changes before locking in.
The calculation is mathematically exact for a standard repayment mortgage with a fixed interest rate and equal monthly payments. Real mortgage offers may include arrangement fees capitalised into the loan, rate changes at the end of a fixed period, or early repayment charges that alter the true total cost. Use this calculator for planning and comparison — verify the exact figures with your lender or mortgage broker before committing.
For a detailed comparison of how a 30-year mortgage stacks up against a 50-year mortgage in terms of monthly cost, total interest and equity build-up:
👉 30 vs 50-Year Mortgage Calculator
For a complete guide to how mortgages work, the true cost of interest front-loading, refinancing break-even analysis and how lenders assess affordability:
30 vs 50-Year Mortgage Calculator — compare two mortgage terms side by side with identical inputs
Savings Calculator — model how quickly you can build a deposit using compound interest on regular monthly contributions
NPV & IRR Calculator — evaluate property investments using discounted cash flow analysis to determine whether the numbers justify the cost