How Car Loan Payments Are Calculated
Auto loans use the same amortization formula as mortgages and personal loans. Your monthly payment is determined by three variables: the loan amount (principal), the annual interest rate, and the loan term in months. The formula is:
Monthly Payment = P × [r(1+r)^n] / [(1+r)^n – 1]
Where P is the principal (car price minus down payment and trade-in), r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments. Each payment covers accrued interest first; the remainder reduces the principal balance.
How to Use This Calculator
Enter the vehicle price, your down payment, any trade-in value you expect from your current vehicle, the annual interest rate you have been offered (or expect), and the loan term. The calculator subtracts the down payment and trade-in from the purchase price to find the loan amount, then computes your monthly payment, total interest, and total out-of-pocket cost over the life of the loan.
Choosing the Right Loan Term
Loan term has a dramatic impact on both your monthly payment and total interest paid. Longer terms lower the monthly payment but cost substantially more in interest:
- 24–36 months: Highest monthly payment, lowest total interest. Best for buyers who can afford the payment and want to minimize borrowing costs.
- 48–60 months: The most common terms. Balance between an affordable payment and reasonable interest costs.
- 72–84 months: Lowest monthly payment, but you will pay significantly more in interest and risk being "underwater" on the loan (owing more than the car is worth) for much of the term, since vehicles depreciate faster than these loans are paid down.
What Is a Good Auto Loan Rate?
Auto loan rates vary based on your credit score, the age of the vehicle (new vs used), and the lender. As a general guide for 2024: buyers with excellent credit (750+) can typically secure rates of 5–7% on new vehicles; good credit (700–749) often qualifies for 7–9%; fair credit (650–699) may see 9–13% or higher. Used car loans typically carry rates 1–3% higher than new car loans for the same credit tier. Shopping multiple lenders — including your bank, credit unions, and manufacturer financing — is the best way to find the lowest rate.
The 20/4/10 Rule for Car Buying
A widely cited rule of thumb for car affordability: put at least 20% down, finance for no more than 4 years, and keep total vehicle costs (payment + insurance) below 10% of monthly gross income. This framework helps avoid being overextended on a depreciating asset. Run the numbers in this calculator using a 48-month term and 20% down to see what payment this rule produces for any vehicle price.
Depreciation and Total Cost of Ownership
The monthly payment is only part of the true cost of car ownership. Depreciation — typically 15–25% of value in the first year and 10–15% per year thereafter — means your car loses value as you pay it down. Other ongoing costs include insurance, fuel, registration, and maintenance. For a comprehensive picture, add these to your monthly payment before deciding how much vehicle you can afford.