Mortgage Interest Calculator
Enter your mortgage details to see the total interest over the loan, and what happens to it if you pay extra.
This calculator gives estimates for information only. It is not financial, tax or legal advice. Real results depend on lender terms, fees and local rules.
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The formula
Total interest = (monthly payment x number of payments) - amount borrowed.
Why the interest is so large
Because you pay interest on the outstanding balance for many years. On 240,000 at 6.5 percent over 30 years the total interest is about 306,000, which is around 56 percent of everything you pay back.
How to cut it
- Choose a shorter term when you can afford the payment.
- Pay a little extra every month, or one extra payment a year.
- Refinance if rates drop enough to cover the fees.
- Put down a larger deposit to borrow less.
Try it
Run the calculation once with no extra payment, then add 100 or 200 a month and compare. The "interest saved" and "paid off after" lines show the difference.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Home price ($): 240000; Interest rate (% a year): 6.5; Loan term (years): 30 | Total interest over the loan: $306,106.77 |
| Home price ($): 240000; Interest rate (% a year): 6.5; Loan term (years): 15 | Total interest over the loan: $136,318.38 |
| Home price ($): 400000; Interest rate (% a year): 5.5; Loan term (years): 30 | Total interest over the loan: $417,616.16 |
Mortgage Interest Calculator: frequently asked questions
What is the difference between interest rate and APR?
The interest rate is the cost of borrowing the money. APR also includes lender fees and some other charges, so it is a better way to compare offers. This calculator uses the interest rate you enter, so add fees separately if there are any.
Does paying extra each month really help?
Yes, a lot. Extra payments go straight to the principal, so you pay less interest on every later month. Try the extra payment box to see how many months and how much interest you save.
Is this financial advice?
No. It gives an estimate from the numbers you enter. Real offers depend on fees, tax and the lender or provider, so check the terms before you commit.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026