How Loan Payments and Amortization Work

Whether it's a car, a personal loan or a business purchase, the same formula decides your monthly payment. Understanding it reveals why interest dominates early on — and why extra payments are so powerful.

The Payment Formula

Most loans are repaid with a fixed monthly payment that covers both interest and principal. The payment comes from the amortization formula:

Where M is the monthly payment, P is the amount borrowed, r is the monthly interest rate (annual rate ÷ 12) and n is the number of payments (60 for a 5-year loan).

Why Early Payments Are Mostly Interest

Interest is charged on the remaining balance, which is largest at the start. Your first payment is mostly interest; your last payment is almost entirely principal. This is called amortization — the balance declines because each payment whittles down the principal.

The Cost of Borrowing

• Principal — the amount you borrowed.
• Interest — the lender's fee, which compounds as the balance stays high.
• Total interest — often 20–50% of the loan amount on long terms.

How Extra Payments Help

An extra payment goes entirely to principal. That reduces the balance faster, so future interest is charged on a smaller amount — shortening the term and cutting total interest. Even $50 a month can remove a year from a typical 5-year loan.

Try It Yourself

Use our Loan Calculator to see your monthly payment, total interest and a full amortization schedule — the formula above is running live on that page.