How Much Interest Will You Pay on a Mortgage?

Borrow $400,000 on a 30-year fixed mortgage at 6.5% and you will pay $510,177.95 in interest — more than the house. Total out the door: $910,177.95. At 6.5% over 30 years, interest comes to about 1.28 times the amount you borrowed.

Most people focus on the monthly payment and never add up the other number. It is worth seeing once, because it reframes every decision about rate, term, and extra payments that follows.

All figures come from the calculator's amortization engine. Run your own loan to see the exact total.

Total interest by loan size and rate

Thirty-year fixed loans. The monthly payment is principal-and-interest only (no taxes or insurance).

$400,000 loan, 30-year fixed
Rate    Monthly P&I   Total interest   Total paid       Interest as % of loan
5.50%   $2,271.16     $417,616.16      $817,616.16      104%
6.00%   $2,398.20     $463,352.76      $863,352.76      116%
6.50%   $2,528.27     $510,177.95      $910,177.95      128%
7.00%   $2,661.21     $558,035.59      $958,035.59      140%
7.50%   $2,796.86     $606,868.89      $1,006,868.89    152%

The same percentages hold for any loan size, because total interest scales linearly with the amount borrowed. So whatever you borrow at 6.5% over 30 years, expect to pay about 128% of it back in interest on top:

30-year @ 6.5%       Total interest
$300,000             $382,633.47
$400,000             $510,177.95
$500,000             $637,722.44

See the full schedule for a $400k loan.

Why interest costs more than the house

It comes down to how amortization front-loads interest. In the early years, the balance is high, so almost all of each payment is interest. On the $400k loan at 6.5%, the very first payment of $2,528.27 is $2,166.67 interest and only $361.61 principal. You do not cross the halfway point — where more of the payment goes to principal than interest — until year 17.

That is the entire reason a 30-year loan is so expensive: you spend the first half of the loan barely denting the balance, and the balance is what generates interest. You can watch the crossover happen month by month in the amortization schedule.

Two levers that cut the total

The total-interest figure is not fixed — two things move it dramatically.

Rate. Each half-point matters more than it looks. On the $400k loan, going from 7.0% to 6.5% saves $47,857.64 in lifetime interest. From 7.5% to 6.5% saves $96,690.94. This is why shopping multiple lenders and quoting points is worth the afternoon — see How Much Does Your Interest Rate Change Your Mortgage Payment?.

Term and extra payments. A shorter schedule slashes the total because interest has less time to accrue. The same $400k loan paid over 15 years instead of 30 costs $227,197.30 in interest — less than half. You do not even need a 15-year loan to get there; an extra $956.16/month on the 30-year reaches the same payoff. The mechanics are in How to Pay Off a 30-Year Mortgage in 15 Years.

Does this include taxes and insurance?

No — and this is important. The totals above are principal and interest only, which is the part of the payment that actually pays off the loan. Your real monthly bill also includes property taxes, homeowners insurance, possibly mortgage insurance (PMI), and HOA dues. Those vary by location and lender and are not "interest" — they are separate costs that do not reduce your balance. The calculator deliberately isolates principal and interest so you can see the true cost of the borrowing itself.

What to do with this number

Seeing the lifetime interest total tends to change behavior in three useful ways:

1. Shop the rate harder. A 0.5% better rate is tens of thousands of dollars, not a rounding error.
2. Take extra payments seriously. Even small ones compound, because every early dollar of principal avoids interest for the entire remaining loan. See How Much Do You Save by Paying Extra on Your Mortgage?.
3. Weigh the term honestly. A 15-year loan more than halves the interest; the trade-off is a higher required payment. The full comparison is in 15- vs 30-Year Mortgage: The Real Math.

The bottom line

At 6.5% over 30 years you pay roughly 1.28x the loan amount in interest — about $510k on a $400k mortgage. Higher rates push that past 1.5x; a shorter schedule or steady extra payments cut it by half or more. The single most useful habit is to look at the total, not just the monthly payment.

Open the calculator, enter your loan, and read the "total interest" figure. Then open the amortization schedule to see exactly when each payment starts working for you instead of the lender.