How to Calculate a Car Payment

Your car payment depends on more than the sticker price of the vehicle. The amount financed, APR and loan term are the primary factors, while taxes, fees, down payments and trade-in equity can also change the final loan balance.

The Three Main Factors

For a standard fixed-rate auto loan, the monthly payment is primarily determined by:

  • Principal or amount financed
  • Annual percentage rate
  • Number of monthly payments

Step 1: Determine the Amount Financed

Start with the negotiated vehicle price.

Then account for your down payment and trade-in equity. After that, add taxes and fees if they will be financed.

For example:

  • Vehicle price: $32,000
  • Down payment: $4,000
  • Trade-in equity: $5,000
  • Taxes and financed fees: $2,500

A simplified amount financed would be approximately:

$32,000 − $4,000 − $5,000 + $2,500 = $25,500

The exact calculation depends on the transaction and applicable state rules.

Step 2: Convert APR to a Monthly Rate

If an auto loan has a 6% APR, a simplified monthly rate for a standard amortizing loan is:

6% ÷ 12 = 0.5% per month

The rate used in the payment calculation is therefore 0.005 in decimal form.

Step 3: Apply the Amortization Formula

A standard fixed-rate payment can be calculated using:

Payment = P × r × (1 + r)n ÷ ((1 + r)n − 1)

Where:

  • P = principal
  • r = monthly interest rate
  • n = number of payments

What Happens With a 0% APR?

If the interest rate is zero, the normal amortization formula is not used because it would involve division by zero.

Instead, the calculation is simple:

Monthly payment = Amount financed ÷ Number of payments

Why Taxes Matter

Sales tax can add thousands of dollars to the transaction price. The taxable amount can also vary depending on the state and whether a trade-in receives a tax credit.

For that reason, a calculator that ignores taxes may produce a substantially different estimate from the final dealership paperwork.

Why Fees Matter

Documentation fees, title charges, registration costs and optional products can also affect the amount financed.

If these costs are rolled into the loan, you will generally pay interest on the financed portion over the life of the loan.

Use Our Calculator

You can avoid doing the math manually with our car loan calculator. Enter your vehicle price, down payment, trade-in value, trade-in payoff, APR, loan term and state.

The calculator provides an estimated monthly payment, amount financed, total payments, total interest and amortization schedule.

Remember That the Estimate Is Not a Lender Quote

An online calculator is useful for budgeting and comparison, but your actual loan terms are determined by the lender. Your credit profile, lender policies, vehicle characteristics, taxes and transaction details can all affect the final numbers.