Loan Calculator

Whether you are taking out a mortgage, an auto loan, or an unsecured personal loan, understanding the true cost of borrowing starts with knowing your monthly payment and total interest. This calculator handles any fixed-rate installment loan — enter the loan amount, annual interest rate, and term in years to see exactly what you will owe each month and how much interest accumulates over the life of the loan. The optional extra monthly payment field reveals how much time and money you can save by paying just a little more each month. For example, adding $200/month to a 30-year mortgage can cut over seven years off the payoff timeline and save tens of thousands in interest.

The standard amortization formula calculates your fixed monthly payment: M = P × r(1 + r)^n / [(1 + r)^n − 1], where P is the loan principal, r is the monthly interest rate (annual APR ÷ 12), and n is the total number of monthly payments. This formula ensures that equal monthly payments will retire the entire balance plus interest by the final payment. When an extra monthly payment is entered, the calculator switches to a month-by-month simulation: each month it charges interest on the current balance, applies the total payment, and reduces the balance by the principal component. The simulation runs until the balance reaches zero, counting the months elapsed and summing total interest charged. The difference between the simulation results with and without the extra payment reveals the time and interest savings.