💰 Loan Interest Calculator
Find out how much total interest you’ll pay over the life of a fixed-rate installment loan.
What This Calculator Does
This calculator shows the total amount of interest you’ll pay over the full life of a fixed-rate installment loan, in addition to the monthly payment and total repayment amount.
The Method
It first calculates the fixed monthly payment using the standard amortization formula: M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments. Total interest is then simply the total of all payments (M × n) minus the original principal.
Why this matters: Two loans with the same monthly payment can end up costing very different amounts in total interest depending on the rate and term — a longer term generally means more total interest even if the monthly payment is lower.
This tool is for general educational and planning purposes only and is not financial advice.