Debt management

Mortgage Interest Calculator

Enter your loan amount, rate and term to see the monthly payment and the total mortgage interest.

  • Free
  • No sign-up
  • Updated for 2026

Mortgage details

$
%
yr
Extra payments
$

per month

Enter the loan amount, rate and term to see the interest.

Worked example

With these example inputs:

  • Loan amount$420,000
  • Interest rate5.5%
  • Loan term15 yr

Monthly payment: $3,432

  • Loan amount$420,000
  • Total interest$197,715
  • Total of payments$617,715
  • Payoff time15 yr

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The default scenario

Here is what the preset values give:

  • Loan amount: $420,000
  • Interest rate: 5.50%
  • Loan term: 15
  • Extra monthly payment: $0
Monthly payment = $3,431.75

What mortgage interest is

Mortgage interest is the cost of borrowing. The lender charges it on your balance. Early payments are mostly interest. Later ones pay down more principal. So interest is the bulk of the cost at first. It appears in the currency you choose.

How it is calculated

The tool takes your loan amount. It applies the monthly rate from the rate. It spreads the loan over your term. So each payment covers interest first. The rest reduces what you owe. The calculator runs the numbers for you.

What the result tells you

The result shows your monthly payment. A higher rate raises it. A longer term raises the total interest. So it shows the payment and the cost. It is a clear monthly figure.

The loan amount

The loan amount is what you borrow. It is the price less your deposit. A bigger loan means a bigger payment. So it also means more total interest. Every dollar borrowed adds to the cost. So a smaller loan saves a lot. Enter the amount you need.

The interest rate

The interest rate drives the whole cost. Even a small rise adds up over years. A higher rate raises every payment. So it lifts the total interest sharply. Shop around for the best rate. So a lower rate saves real money. Use the rate you are offered.

The extra monthly payment

An extra monthly payment cuts the interest. It goes straight at the balance. So you clear the loan sooner. It also saves years off the term. Even a small extra adds up fast. So paying more saves a lot. Add what you can each month.

How to use it

Enter your loan amount first. Add the rate and the term. Read the monthly payment in the currency you choose. See the total mortgage interest too. Then try different terms. Compare a few rates. Use it to see the true cost.

What falls outside

It has a few clear limits. It assumes a fixed rate throughout. Real rates can change on some loans. It ignores tax, insurance, and fees. Your real bill may be higher. So treat it as an estimate. So read the result with a clear head.

Common mistakes to avoid

A common mistake is ignoring the total interest. The monthly payment is only part. Another is picking too long a term. That piles on interest over time. Some skip shopping for a rate. Others forget tax and insurance.

What the figure does not cover

Use this to see the true cost. Remember the rate drives the interest. Shop around for the best rate. Add an extra payment to save years. Watch the total, not just the payment. Do not forget tax and insurance. A careful check guides your view.

Frequently asked questions

How much interest does a mortgage cost?

Over a long term the interest can rival the loan itself. A $300,000 mortgage at 6.5% over 30 years pays well over $380,000 in interest across the life of the loan.

How can I pay less interest?

A lower rate, a shorter term or extra principal payments all cut the total. The donut and chart show how your payments split between interest and principal over time.