How Loan Payments Work: Amortization and Interest Explained

Principal vs. interest

Every payment does two jobs: it pays the interest that accrued on the outstanding balance, and it repays a chunk of the principal you borrowed. Interest is charged on what you still owe, so when the balance is largest — at the start — the interest portion is largest too, and little goes to principal.

The amortization schedule

An amortization schedule lists every payment and shows the principal-to-interest split shifting month by month. Consider a $20,000 car loan at 7% over 5 years, with a payment near $396. In the first month, roughly $117 is interest and $279 is principal; by the final year almost the entire payment repays principal.

The monthly payment formula

The fixed payment comes from one formula: M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the amount borrowed, r is the monthly interest rate (annual rate ÷ 12), and n is the number of payments. It looks dense, but it just guarantees a level payment that clears the loan exactly on schedule.

Frequently asked questions

Why does paying extra early save so much interest?

Extra payments go straight to principal, shrinking the balance that all future interest is charged on — the earlier you do it, the more interest you cut.

What's the difference between APR and interest rate?

The interest rate prices the borrowing itself; the APR folds in fees, so it's a fuller measure of the yearly cost and better for comparing offers.

Does a longer term make a loan cheaper?

It lowers the monthly payment but raises the total interest, because you owe money for longer. Cheaper per month, more expensive overall.

Why is my early balance barely moving?

Because early payments are mostly interest. Only a small slice reduces principal at first; the balance falls faster as interest shrinks later on.