How the Loan Calculator works
Any fixed-rate loan — personal, business, medical, family — follows the same amortization math. The early payments are mostly interest, and the balance only falls quickly in the back half of the term. Seeing the total interest next to the monthly payment is usually what changes someone's mind about the term length.
Payment = P × r ÷ (1 − (1 + r)^−n), where P is the amount borrowed, r is the monthly rate (APR ÷ 12) and n is the number of monthly payments.