How much interest will I pay on my mortgage?

The three numbers that set your interest

Total interest scales with all three. Double the loan and the interest doubles. Stretch the term and the interest grows even though the payment falls: the balance shrinks more slowly, so more of each payment goes to interest for longer. The rate does the most damage at the start, when the balance is biggest.

The example loan is $400,000, picked for clean math. Scale it: a $300,000 loan costs three quarters of every figure here, and a $500,000 loan adds a quarter.

Total interest at five rates

Worked example: $400,000 at 7.40% for 30 years

The standard amortization formula gives $2,770 a month. Of the first payment, $2,466.67 is interest: 89 cents of every dollar. Only $303 goes to the loan itself. The split improves from there, because each payment shrinks the balance a little and the next interest charge lands on a smaller number.

Hold the loan to the end and the totals are $997,027 repaid, of which $597,027 is interest. About 60 cents of every repaid dollar is interest. Most owners sell or refinance before year 30, so the full figure rarely lands in one pocket.* The early years are still the expensive ones whenever you hold the loan.

What an extra $100 does

Pay $2,870 instead of $2,770 on the same loan and the picture changes fast. The loan ends in 320 payments instead of 360, about 3 years and 4 months early, and total interest falls to $516,407. That is $80,620 kept for $100 per payment.

Extra payments work because they attack the balance in the years when the balance is biggest. The same $100 matters far less in year 25, when most of the payment is already principal.

The 15-year question

The same $400,000 at 7.40% over 15 years costs $3,685 a month, $916 more than the 30-year payment, but total interest falls to $263,364. The shorter term keeps $333,663 in the borrower's pocket instead of the lender's. The catch is cash flow: the higher payment has to survive job losses and bad years, not just good ones.*

How to read this without over-reading it

Three limits. First, 7.40% is a survey average for strong-credit conforming borrowers; your quote depends on your credit, down payment, loan type and lender. Second, everything here is principal and interest only: property tax, insurance and any mortgage insurance sit on top. Third, the 30-year totals assume you never sell, refinance or prepay, which is not how most loans actually run.*

What the math supports is narrow: at 7.40%, interest is the majority of what a 30-year borrower repays, and small extra payments early move the total by tens of thousands.

Limits

Educational explanation, not tax, legal or investment advice. Examples are labelled. Nothing here promises a result.

Common questions

How much interest will I pay on a $400,000 mortgage?

At 7.40% over 30 years, about $597,027 in interest on top of the $400,000 borrowed. The rate, term and loan size set the answer; at 6% the same loan costs about $463,353 in interest.

How much of my first payment is interest?

At 7.40%, $2,466.67 of the first $2,770 payment is interest, about 89%. The share falls as the balance shrinks.

Does an extra $100 a payment really matter?

On the example loan it saves about $80,620 in interest and ends the loan about 3 years and 4 months early. Extra payments early in the loan do the most work.

Is a 15-year mortgage cheaper in interest?

Yes, by a wide margin: about $263,364 versus $597,027 on the same $400,000 at 7.40%, a saving of about $333,663. The payment rises about $916 to $3,685.

Related questions, answered

Where does the 7.40% figure come from?

Freddie Mac's Primary Mortgage Market Survey of lenders, series MORTGAGE30US, which reports an average 30-year fixed rate each week. The reading for the week of October 15, 2026 is 7.40%.

Why is interest more than half of what I repay?

Because the balance is largest at the start, interest takes most of the early payments, and it takes years before principal dominates. Over 30 years at 7.40% those interest-heavy years add up to 149% of the original loan.

Source: Freddie Mac, 30-year fixed rate mortgage average, series MORTGAGE30US, via FRED, retrieved October 21, 2026