What is my total mortgage interest?
See how much interest your mortgage charges in total, in the first payment, and in each year of the loan.
- Total interest
- $408,142.36
A $320,000.00 mortgage at 6.5% over 30 years charges $408,142.36 of interest in total.
- Monthly payment
- $2,022.62
- Interest in the first payment
- $1,733.33
- Interest in the first year
- $20,694.69
- Interest share of all payments
- 56.1%
- Principal repaid
- $320,000.00
- Total paid
- $728,142.36
- Paid off in
- September 2056
- Months
- 360
Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.
Total interest: $408,142.36. A $320,000.00 mortgage at 6.5% over 30 years charges $408,142.36 of interest in total.
How much of what you pay is interest?
How much interest do you pay each year?
What does every payment look like?
The results are estimates for information only. They are not financial, tax, or legal advice. Check the numbers with your lender or a qualified professional before you decide. Terms of use
How to calculate
Computes the total interest on a fixed-rate mortgage, the interest in the first payment and the first year, the interest paid each year, and the interest an extra monthly payment saves.
Example with the default inputs (Loan amount $320,000.00, Interest rate 6.5%, Loan term (years) 30, Extra each month $0.00, Loan start date September 30, 2026) on the example date Wednesday, September 30, 2026: A $320,000.00 mortgage at 6.5% over 30 years charges $408,142.36 of interest in total.
Method: payment = L × r ÷ (1 − (1 + r)^−n), with L the loan, r the rate ÷ 12, and n the months; each month, interest = balance × r and the rest of the payment lowers the balance; total interest is the sum.
- The rate is fixed and interest is charged monthly at the yearly rate ÷ 12.
- The first payment is one month after the start date; the last payment clears the balance.
- Nothing is rounded to the cent between months; only the display is rounded.
- Property tax, insurance, mortgage insurance, and fees are not included.
Worked examples
Each example is checked against the calculator on every build.
- Loan amount $320,000.00, Interest rate 6.5%, Loan term (years) 30 gives Monthly payment $2,022.62, Total interest $408,142.36, Interest in the first payment $1,733.33, Interest in the first year $20,694.69, Total paid $728,142.36.Source: CFPB, How does paying down a mortgage work? (interest on the balance each month)
- Loan amount $320,000.00, Interest rate 6.5%, Loan term (years) 15 gives Monthly payment $2,787.54, Total interest $181,757.84.
- Loan amount $120,000.00, Interest rate 0%, Loan term (years) 10 gives Monthly payment $1,000.00, Total interest $0.00, Interest share of all payments 0%, Interest in the first year $0.00.
- Loan amount $320,000.00, Interest rate 6.5%, Loan term (years) 30, Extra each month $300.00 gives Total interest $269,696.46, Interest saved by paying extra $138,445.90, Months saved by paying extra 106.
How it works
Write L for the loan amount, r for the yearly rate ÷ 1200 (the monthly rate as a decimal), and n for the number of months (years × 12).
- Payment. P = L × r ÷ (1 − (1 + r)^−n). At 0% the payment is L ÷ n.
- Each month (payment k = 1, 2, 3, …): interest = balance before the payment × r. If this is payment n, or P + extra − interest is at least the balance, the payment clears the balance (principal = the balance). Otherwise principal = P + extra − interest, and the new balance is the old balance minus the principal.
- Totals. Total interest is the sum of every month's interest. The interest in the first payment is L × r. The interest in the first year is the sum over payments 1 to 12 (or over all payments, if an extra amount ends the loan sooner). The total paid is L + total interest, and the interest share is total interest ÷ total paid × 100.
- Extra payments. With an extra amount, the interest saved is the total interest without the extra minus the total interest with it, and the months saved is n minus the number of payments with the extra.
- Paid off in (with a start date): the month of the last payment. Payment k is dated k months after the start date, so the last one is (number of payments) months after it.
Assumptions
- The rate is fixed for the whole loan.
- Interest is charged monthly at the yearly rate ÷ 12, not by the day.
- The first payment is one month after the start date.
- Nothing is rounded to the cent between months; only the display is rounded.
- The payment here is principal and interest only. Property tax, home insurance, mortgage insurance, and fees are not included.
- The default rate is an example, not a current market rate.
Worked examples by hand
$320,000 at 6.5% over 30 years. r = 0.065 ÷ 12 = 0.00541667 and n = 360. (1 + r)^−360 = 0.143025, so P = 320,000 × 0.00541667 ÷ 0.856975 = $2,022.62. The first month's interest is 320,000 × 0.00541667 = $1,733.33, so principal is $289.28 and the balance becomes $319,710.72. Adding the interest of payments 1 to 12 gives $20,694.69 for the first year. Over 360 payments the loan repays $320,000 and the payments total 360 × 2,022.618 = $728,142.36, so total interest is $408,142.36.
The same loan over 15 years. n = 180 and (1 + r)^−180 = 0.378186, so P = 320,000 × 0.00541667 ÷ 0.621814 = $2,787.54. The payments total 180 × 2,787.544 = $501,757.84, so total interest is $181,757.84.
$120,000 at 0% over 10 years. No interest is charged, so the payment is 120,000 ÷ 120 = $1,000 and total interest is $0.
$320,000 at 6.5% over 30 years with $300 extra a month. Each month pays $2,322.62 toward the loan. Running the monthly rule, the balance reaches 0 after 254 payments, 106 months sooner, with $269,696.46 of interest. That is $138,445.90 less than the $408,142.36 without the extra.
Other questions people ask
How is mortgage interest calculated each month?
Each month the lender charges the balance you still owe times the yearly rate ÷ 12. On a $320,000 loan at 6.5%, the first month's interest is 320,000 × 0.065 ÷ 12 = $1,733.33. The rest of the payment lowers the balance, so the next month's interest is a little smaller.
Why is most of my early payment interest?
The payment stays the same, but interest is charged on the balance, which is largest at the start. On a 30-year loan at 6.5%, about 86% of the first payment is interest. As the balance falls, more of each payment goes to principal.
How much interest does a 15-year mortgage save?
A shorter term means a higher payment but far less interest. $320,000 at 6.5% costs $408,142 of interest over 30 years and $181,758 over 15 years. In real life a 15-year loan often has a lower rate too, which saves more.
Does paying extra each month reduce interest?
Yes. Extra money goes straight to principal, so every later month charges interest on a smaller balance. $300 extra a month on $320,000 at 6.5% over 30 years saves $138,446 of interest and ends the loan 106 months sooner. Check that your loan has no prepayment penalty first.
Is mortgage interest tax deductible?
Mortgage interest can be deducted if you itemize, for up to $750,000 of mortgage debt on loans taken after December 15, 2017 (IRS Publication 936). Most people take the standard deduction instead, so check whether itemizing helps you. This page shows the interest, not a tax saving.
Why does my lender's number differ a little?
Lenders round each payment to the cent, and some loans charge interest by the day. This page keeps full precision and charges a month's interest as the balance × rate ÷ 12, so totals can differ by a few dollars.