Amortization, Explained: Where Your Payment Actually Goes

The fixed payment with a moving split

Amortization is the schedule that pays a loan off in equal installments. The payment never changes — but what the payment does changes every single month. Interest is charged on whatever balance you still owe. At the start the balance is at its largest, so interest eats most of the payment and only a sliver reduces the loan. Each month the balance drops a little, so the next month's interest charge drops a little, and a little more of the same payment reaches the principal. The split tilts, slowly and then quickly, until the final payment is almost all principal.

That is the entire mechanism. Everything surprising about mortgages — the glacial first years, the galloping last years — falls out of it.

A $360,000 loan at 6.5% over 30 years

Take a $360,000 mortgage at 6.5% APR on a 30-year term. The monthly principal-and-interest payment is $2,275.44. Here is where the money actually goes:

Month one is the fact that surprises everyone: 86% of the first payment is interest — $1,950.00 of the $2,275.44 — because 6.5% of $360,000, divided by twelve months, is a big number, and the balance has not yet moved. After a full year of payments totalling over $27,000, the balance has fallen by just $4,023.81. The rest was the cost of renting the money. And across the whole loan, the interest totals $459,160.16 — more than the amount borrowed.

Our Amortization Calculator prints this schedule month by month for any loan — and lets you add extra monthly payments, or a one-time lump sum in a chosen month, to watch the schedule reshape itself.

The crossover: month 233

On this loan, the principal portion of a payment first exceeds the interest portion in month 233 — more than 19 years in (year 19.4, to be precise). Until that month, every payment you make sends more money to the lender as interest than it removes from your debt. This is why the first years of a 30-year mortgage build equity so slowly, and why selling or refinancing in year three can feel like the balance barely moved: it genuinely didn't.

Why the final years fly

The tilt never stops accelerating. With the balance small, interest takes a shrinking bite, so nearly the whole $2,275.44 lands on principal, which shrinks the balance faster, which shrinks interest further. Borrowers who reach the last five years of a mortgage often watch the balance fall faster than they expected — it is the same schedule, finally working at full speed. The math was never against you or for you; it was just waiting for the balance to drop.

What changes the schedule

Three levers reshape an amortization table. A lower rate shrinks the interest bite from month one, so principal progress starts faster. A shorter term forces a bigger payment, but the interest total falls dramatically because the balance is attacked from the start. And extra payments — the one lever available after signing — go entirely to principal, every cent, pulling the whole schedule forward. The Mortgage Calculator adds property tax and insurance to the same math for the full housing payment, and the Loan Calculator solves for whichever of payment, amount, term or rate you are missing, on any kind of loan.

How to read a real amortization table

Find the row for your next payment. Look at its interest figure: that is the true monthly cost of carrying your loan right now — the rent on the money. Then look at the principal figure: that is all your equity grows by this month if you pay exactly the scheduled amount. Finally, scan down to the crossover row, where principal passes interest. Knowing those three numbers — current interest, current principal, crossover month — tells you more about your loan than the balance alone ever will.