How to Calculate Your Auto Loan Payment Step by Step

Understanding the Auto Loan Payment Formula

To calculate a monthly auto loan payment, you need three key inputs: the loan amount (principal), the annual interest rate, and the loan term in months. The standard formula for equal monthly payments is:

M = P × [r(1+r)^n] / [(1+r)^n – 1], where M is the monthly payment, P is the principal, r is the monthly interest rate (annual rate divided by 12), and n is the number of monthly payments.

This formula assumes a fixed interest rate and equal payments over the life of the loan. It works for most conventional auto loans, whether for a new or used car.

Sources: TaxAct, North Shore Bank, Tidemark Federal Credit Union

Required Inputs: Amount, Rate, Term

The loan amount is the total cost of the vehicle you finance—including the purchase price, taxes, and fees—minus any down payment or trade-in value. If you roll taxes and fees into the loan, they become part of the principal and accrue interest over time.

The annual interest rate (often called APR) determines the cost of borrowing. The monthly rate is the annual rate divided by 12. A lower rate reduces your monthly payment and total interest.

The loan term is the number of months you have to repay the loan. Longer terms (e.g., 72 months) lower the monthly payment but increase the total interest paid. Shorter terms (e.g., 36 months) do the opposite.

• Loan amount (principal): total vehicle cost minus down payment, plus any add-ons rolled into the loan.
• Annual interest rate (APR): the yearly cost of borrowing, including fees.
• Loan term in months: the duration of the loan.

Sources: TaxAct, North Shore Bank, Tidemark Federal Credit Union

Example: New Car Loan Calculation

Let's work through an example for a new car. Suppose you finance $25,000 at 9% APR for 48 months. Using the formula, the monthly payment is approximately $622. Over four years, you will make 48 payments, totaling $29,862. That means the total interest paid is $4,862.

Now consider the same $25,000 loan at 9% APR but extend the term to 72 months. The monthly payment drops to about $451, making it easier on your monthly budget. However, over 72 months you will pay $32,446 in total, resulting in $7,446 in interest—nearly $2,600 more than with the 48-month term.

Sources: NerdWallet

Example: Used Car Loan Calculation

For a used car, the process is the same. Consider a $15,000 loan at 7.5% APR with a four-year term (48 months). The monthly payment is $362.69. The finance charge—the total interest paid—is $2,409.12.

This example shows how a larger down payment or a lower interest rate can reduce both the monthly payment and the total finance charge. Even a small change in the rate or term can have a significant impact over the life of the loan.

Sources: North Shore Bank

Accounting for Down Payment and Trade-In

A down payment reduces the loan amount, which in turn reduces both your monthly payment and the total interest you pay. The same applies to the value of a trade-in: it lowers the principal you need to finance.

For example, if you're buying a car with a total price of $30,000 and you make a $5,000 down payment, your loan amount is $25,000. That reduction directly lowers your monthly payment and interest charges.

When you calculate your payment, always subtract any down payment and trade-in value from the total purchase price to get the loan amount.

Sources: TaxAct, Consumer Financial Protection Bureau, Kelley Blue Book

a monthly payment

Your monthly car payment isn't just the principal and interest. It can also include taxes, title and registration fees, and other charges—if you choose to roll them into the loan rather than paying them upfront.

The payment you see in a calculator often assumes these costs are included in the loan amount. If you pay them separately at the dealership, your loan amount and monthly payment will be lower.

Be aware that taxes, title, and fees can add hundreds or thousands of dollars to the total cost. For example, a typical dealership fee averages around $466, and title and registration fees vary by state (e.g., $38.75 for a passenger vehicle in North Carolina).

• Principal and interest: the core of your payment.
• Taxes and fees: sales tax, title, registration, and any dealership charges.
• Add-ons: extended warranties or other products rolled into the loan.

Sources: Consumer Financial Protection Bureau, Skyla Credit Union, TaxAct

fees and taxes

Taxes, title, and registration fees can be paid upfront or financed. If you finance them, they increase the loan amount and, as a result, you pay interest on them over the life of the loan.

The total cost of a vehicle includes more than the sticker price. You must add taxes, fees, and the total interest paid on the loan. This is the 'true cost' of buying the car on credit.

When comparing loan offers, look at the APR, not just the monthly payment. A lower APR with a shorter term can save you thousands in interest, even if the monthly payment is higher.

Sources: Consumer Financial Protection Bureau, J.D. Power, Experian

Comparing Loan Scenarios

To see the effect of different rates and terms, you can use the formula to compare scenarios. The table below shows how changing the term affects monthly payment and total interest for a fixed loan amount and rate.

Always recompute the numbers with your own figures. The formula is straightforward: plug in your loan amount, monthly interest rate, and number of months to find the payment, then multiply by the number of months to get the total paid and subtract the principal to find total interest.

Sources: NerdWallet