How to use this mortgage calculator
Start with the three numbers that matter most: the home price, your down payment (or deposit), and the interest rate you've been quoted. Results update instantly, so drag the sliders to see how a cheaper home or a better rate changes your repayment.
- Pick a repayment frequency. Most US loans are monthly. In Australia and New Zealand, fortnightly and weekly repayments are common.
- Open "More options" to add property tax or council rates, home insurance, mortgage insurance and HOA or strata fees. This turns a principal-and-interest figure into what actually leaves your account.
- Try an extra repayment. Even a small amount added to every repayment goes straight to principal. The results show the interest you save and your new payoff date.
- Share or save your scenario. "Copy link" saves every input in the URL, so you can send it to a partner or broker, or bookmark several scenarios to compare.
The formula behind your repayment
M = P × r ÷ (1 − (1 + r)−n) M = repayment per period · P = loan amount · r = annual rate ÷ repayments per year · n = years × repayments per year
The formula sets a repayment that is the same every time and brings the balance to exactly zero on the last repayment. Each period, interest is charged on the balance that's left. Whatever remains of your repayment then reduces the principal. Because the balance is largest at the start, early repayments are mostly interest. Halfway through a 30-year loan you've usually repaid well under half the principal.
Worked example
A $450,000 home with a $90,000 down payment means borrowing $360,000. At 6.5% over 30 years, monthly, the rate per period is 0.065 ÷ 12 = 0.5417% across 360 repayments. That gives a repayment of about $2,275.44. Over the full term you'd repay roughly $819,000, so about $459,000 is interest, more than the amount you borrowed.
Add an extra $200 a month and the same loan is paid off about six years sooner, saving roughly $109,000 in interest. Try it in the calculator above.
What really drives the cost of a mortgage
The interest rate
On a $360,000, 30-year loan, every 1 percentage point of interest adds about $240 to the monthly repayment and around $87,000 to the total interest. Shopping around, improving your credit score or paying points can be worth thousands. Use our loan comparison calculator to compare two offers properly.
The loan term
A longer term lowers the repayment but raises the total cost sharply. Switching from 30 to 25 years on the example above raises the monthly repayment by about $155, and cuts total interest by roughly $90,000. A 15-year term brings total interest down to about $204,000, less than half the 30-year figure.
Your down payment
A bigger deposit shrinks the loan, the interest charged on it and often the rate itself. Crossing the 20% mark (an LTV of 80%) usually removes mortgage insurance altogether. If you're still saving, the savings goal calculator shows how long it will take.
The costs around the loan
Property tax, insurance and fees can add 20–40% to a repayment in high-tax areas. They don't shrink as you pay down the loan, and they often rise each year, so include them before deciding what you can afford.
Ways to pay your mortgage off sooner
- Extra repayments: any amount above the minimum reduces principal immediately. Check your loan allows it without penalties.
- Half-monthly every fortnight: quietly adds a 13th monthly repayment each year.
- Lump sums: tax refunds or bonuses applied early in the loan have the biggest effect. Model one with the extra repayments calculator.
- Offset or redraw accounts (common in Australia): savings held against the loan reduce the balance interest is charged on.
- Refinance when rates fall, but keep your repayment the same so the saving shortens the loan. The refinance calculator finds your break-even point.
Rule of thumb: many lenders like housing costs below about 28% of gross income and total debt repayments below 36–43%. Check yours with the home affordability and debt-to-income calculators.
Mortgage terms in different countries
This calculator works for any country: switch currency at the top of the page. The words differ more than the maths:
| Concept | United States | Australia / NZ | United Kingdom |
|---|---|---|---|
| Upfront cash | Down payment | Deposit | Deposit |
| Insurance on low-deposit loans | PMI | LMI (one-off) | Usually priced into the rate |
| Local property charges | Property tax | Council rates | Council tax |
| Typical term | 30 years fixed | 30 years, often variable | 25 years, 2–5 year fixes |
Frequently asked questions
How is a mortgage repayment calculated?
Is fortnightly or weekly repayment cheaper than monthly?
What does PITI mean?
How much should my down payment or deposit be?
Does this calculator work for variable-rate loans?
Are my numbers saved or sent anywhere?
This calculator gives estimates for education and planning. It is not financial advice, and your lender's figures may differ. See how we calculate.