Reading Your Amortization Schedule: Why Your Loan Payment Split Shifts Over Time

Every loan payment is split two ways: part pays down the principal (what you borrowed), part pays interest (the cost of borrowing). Early in a loan, most of your payment goes to interest. Late in a loan, most goes to principal. This guide explains why — and how to read the schedule our Loan & Mortgage Calculator generates.

The Core Formula

M = P [r(1+r)^n] / [(1+r)^n − 1] — where M is monthly payment, P is loan principal, r is monthly interest rate, and n is number of payments.

Why the Interest/Principal Split Shifts Over Time

Interest is charged on the remaining balance. Early on, the balance is high, so interest takes a bigger bite. As the balance shrinks, less of each payment goes to interest and more goes to principal — even though your total payment stays exactly the same every month.

What to Look For in Your Schedule

Three things worth tracking: the month where principal finally overtakes interest as the larger portion of your payment; the total interest paid over the full loan term versus the amount borrowed; and the effect of one extra payment per year on total interest, which is often larger than people expect.

Common Mistake: Judging a Loan by the Monthly Payment Alone

A lower monthly payment doesn't always mean a cheaper loan. A longer term lowers the payment but usually increases total interest paid — the "total interest paid" figure is the number that actually matters for cost comparison, not the payment size.