Debt Payoff Calculator

Most people carrying credit card balances, personal loans, or car financing only pay the minimum each month, unaware that a small payment increase dramatically shortens the repayment timeline and slashes total interest. This calculator applies the standard loan amortisation formula to show exactly how many months your debt will last and precisely how much interest you will pay in total. Enter your current balance, the annual interest rate, and your planned fixed monthly payment to get an immediate, accurate answer. You can experiment by adjusting the monthly payment to see how an extra $25, $50, or $100 per month reshapes your payoff date and interest burden — a powerful way to find the most impactful debt-reduction strategy.

The monthly interest rate r is the annual rate divided by 12. Months to payoff uses the closed-form amortisation formula: n = −ln(1 − r × P ÷ PMT) ÷ ln(1 + r), where P is the current balance and PMT is the monthly payment. Math.ceil rounds up to the next whole month. Total interest is then computed by simulating each month step-by-step: interest this month = remaining balance × r; new balance = old balance + interest − payment. This simulation handles the smaller final payment correctly — if the balance goes negative in the last month, the excess interest is subtracted back. If the monthly payment is less than or equal to r × P (the monthly interest alone), the debt can never be paid off and an error is shown.