Car Interest Calculator

Written by Great Medico

Updated September 27, 2026 •2 min read

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The sticker price is only part of the cost of financing a car. The Car Interest Calculator estimates the monthly payment and total interest for a standard fixed-rate amortizing loan, helping you see how rate and term affect the amount repaid.

What this calculator does

Choose a currency and enter the loan amount, annual interest rate, and loan term in years. The calculator converts the annual rate to a monthly rate, calculates the level monthly payment, and reports total interest and total repayment over the modeled term.

How to use the Car Interest Calculator

Enter the amount actually financed rather than the vehicle’s full sticker price if a down payment, trade-in, rebate, or upfront taxes reduce the loan principal. Use the annual percentage rate appropriate to the loan model and enter the scheduled term. If the annual interest rate is zero, the calculator simply divides principal by the number of monthly payments.

Car loan interest formula

For a positive monthly rate r and n monthly payments, the standard amortizing payment is P × r ÷ [1 − (1 + r)⁻ⁿ], where P is the loan principal. Total repayment is monthly payment × number of payments, and total interest = total repayment − principal.

Worked example

For a $25,000 loan at 6% annual interest over 5 years, the modeled monthly payment is about $483.32. Across 60 payments, total repayment is roughly $28,999, so total interest is about $3,999, subject to rounding and the lender’s exact payment schedule.

How to interpret the result

A longer term usually lowers the monthly payment but can increase total interest because the balance remains outstanding longer. A lower rate reduces both the monthly financing cost and total interest. Comparing scenarios is often more useful than looking at the payment alone.

Limitations and practical notes

This calculator models a conventional fixed-rate amortizing loan. It does not automatically include sales tax, registration, dealer fees, insurance, add-on products, prepayment charges, balloon payments, irregular payment dates, or lender-specific compounding and rounding rules. Use the lender’s official disclosure for the contractual payment and total cost.