How mortgage payments work
Last updated: 2026-08-14
Borrow $400,000 over 30 years at 6.5% and the payment is about $2,528 a month. Of that first payment, $2,166.67 is interest and $361.61 reduces what you owe. You have paid a mortgage payment and your balance has moved by less than a tenth of it.
That is not a trick. It is arithmetic, and understanding it changes how you read every other mortgage decision.
Where the payment comes from
The principal-and-interest payment is fixed by three numbers: the amount borrowed, the monthly rate, and the number of payments.
P is the loan, r is the annual rate divided by 12, and n is the number of monthly payments. At 6.5% the monthly rate is 0.541667%, and over 360 payments that produces the $2,528 figure. The formula solves for the one payment that clears the loan exactly on the final month — nothing more elegant than that.
Why the first payment is nearly all interest
Interest each month is charged on whatever you still owe. In month one you owe the whole $400,000, so the interest is $400,000 × 0.541667% = $2,166.67. The payment is $2,528.27. What is left over, $361.61, is the only part that touches the balance.
| Payment 1 | Amount | Share |
|---|---|---|
| Interest | $2,166.67 | 86% |
| Principal | $361.61 | 14% |
| Payment | $2,528.27 | 100% |
Next month you owe $361.61 less, so the interest is fractionally smaller and the principal share fractionally larger. The payment never changes. What it is doing changes every single month.
What actually moves the payment
Rate. On this loan, each one-percentage-point move is worth roughly $250 a month. That is why rate shopping repays the effort quickly.
Term. A shorter term raises the payment and cuts total interest sharply, because the balance spends far less time accruing. A longer term does the reverse, and the lower payment is bought with a larger total.
Amount borrowed. A larger down payment reduces the loan directly, and crossing 20% of the property value usually removes mortgage insurance as well, which is often worth more per month than the interest it saves.
The payment is not the housing cost
Principal and interest amortize the loan. Property tax, homeowners insurance, mortgage insurance and HOA dues sit beside it, are often collected with it through escrow, and reduce the balance by nothing at all.
On a $400,000 home, property tax at 1.1%, insurance at $1,800 a year and PMI at 0.5% of the loan add roughly $684 a month. That turns a $2,528 loan payment into about $3,212 of actual housing cost — 27% more than the number most people quote.
Compare loans on principal and interest, because that is the part the loan controls. Budget on the full figure, because that is the part your account sees.
Run your own numbers
The mortgage calculator estimates a full payment with taxes, insurance and PMI, and keeps principal and interest visible separately. The amortization calculator shows the month-by-month balance, and the affordability calculator works backwards from income.
Related reading: mortgage amortization explained and taxes, insurance and PMI.
What the rate does to the payment
A mortgage payment is far more sensitive to rate than most buyers expect, because the rate applies to a large balance over a long period.
| Rate | Monthly principal and interest | Total interest over the term |
|---|---|---|
| 5.0% | $1,610 | $279,767 |
| 6.0% | $1,799 | $347,515 |
| 6.5% | $1,896 | $382,633 |
| 7.5% | $2,098 | $455,090 |
Two and a half points of rate adds nearly five hundred dollars a month and one hundred and seventy-five thousand dollars over the term. That is the same house at a different price.
Common questions
Why is so much of my early payment interest?
Interest is charged on the outstanding balance, which is at its largest at the start. Every payment is the same size but the split moves steadily toward principal as the balance falls.
Does a shorter term always cost less?
In total interest, almost always. In monthly payment, never. A fifteen-year loan costs far less overall and demands a much larger monthly commitment, so the question is affordability rather than arithmetic.
What is included in the monthly payment?
Principal and interest are the loan itself. Most lenders also escrow property tax and homeowners insurance, and add mortgage insurance where the deposit was small, which is why the amount leaving your account exceeds the quoted principal and interest.
Does paying biweekly help?
It results in twenty-six half-payments, which is one extra full payment a year. The saving comes from that extra payment rather than from the frequency, and paying one-twelfth extra each month achieves the same thing.
Related reading
The rest of this series, and the calculators that let you run the idea on your own numbers.
More mortgage guides
Try it with your figures
See also all guides, every calculator, and the calculation methodology behind these estimates.