Car Payment Calculator: Estimate Your Monthly Cost

A car payment calculator estimates your fixed monthly loan payment from the amount financed, annual percentage rate (APR), and loan term. Enter those figures to see the monthly payment and total interest; the result is an estimate of loan costs, not the full cost of owning a car.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual APR to a monthly rate, then calculates the payment needed to repay the principal and interest in equal monthly installments:

Payment = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the loan amount, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200 = 0.0066667 per month.
• n is the number of monthly payments, calculated as loan term in years × 12.
• Payment is the monthly amount in dollars, rounded to the nearest cent.

Total interest is calculated as monthly payment × number of payments − loan amount. Because this total uses the payment rounded to cents, it reflects the calculator’s displayed payment. A lender may adjust the final installment slightly to settle the remaining balance.

Worked Example

Using the calculator’s default inputs—$20,000 financed, 8% APR, and a 5-year term:

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Find the number of payments: 5 × 12 = 60.
3. Apply the formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. Round the monthly payment to cents: $405.53 per month.
5. Calculate total interest using that rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The APR stays fixed throughout the loan.
• Payments are equal, made monthly, and begin one month after the loan starts.
• Interest is calculated monthly at APR divided by 12.
• The calculation excludes fees, taxes, insurance, and other ownership costs unless they are included in the amount financed.

What to Enter and When to Use It

Use the loan amount that would actually be financed, not automatically the vehicle’s advertised price. A car’s out-the-door price may include charges or taxes, while a down payment, trade-in credit, or other money paid upfront can reduce the amount borrowed. If these figures are not yet known, the calculator can still show how a hypothetical principal, rate, and term combine.

For a useful estimate, obtain the APR and proposed term from the lender’s written figures or quote. APR is an annualized borrowing-cost measure, but the calculator treats it as a fixed rate applied monthly; it does not independently determine what APR a lender may offer. Rates and fees are inputs, so use the actual figures supplied for the particular loan rather than treating the example defaults as a prediction.

• To compare hypothetical terms, change only the term and keep the loan amount and APR the same.
• To see the effect of a different financed amount, adjust the principal while holding the other inputs constant.
• For a proposed monthly payment, compare it with the calculated loan installment separately from fuel, maintenance, insurance, registration, and parking expenses.

How to Read the Results and Common Mistakes

The monthly payment is the scheduled installment in the simplified model. Total interest is the modeled interest paid over all scheduled installments, not a separate monthly charge. A longer term usually reduces the required installment for the same principal and rate, but it also means interest accrues over more payment periods. The figures alone do not show the vehicle’s depreciation or the borrower’s complete transportation costs.

A common mistake is entering the vehicle’s full price as the loan amount even when a down payment or trade-in reduces the balance. Another is entering 8 for 8% but then dividing by 12 in the formula; this calculator handles the conversion internally by dividing APR by 1,200. Enter APR as a percentage, such as 8, not as a decimal such as 0.08.

Rounding can create small differences between an online estimate and a lender’s schedule. The calculator rounds the regular payment to cents and uses that rounded amount to calculate total interest. Actual contracts may use specific payment dates, daily interest calculations, fees, or a slightly different final payment. Check whether a quoted amount financed includes every item being financed.

What the Calculator Does Not Include

This is a level-payment calculation for a conventional fixed-rate installment loan. It does not model a variable rate, skipped or irregular payments, extra principal payments, a balloon payment, a separate final balance, or fees charged outside the loan. It also does not calculate a vehicle’s full ownership cost or determine whether a particular loan will be offered or approved.

If charges are rolled into the loan, include them in the principal only when you know they are part of the amount financed. To estimate an early payoff or the effect of extra payments, a balance schedule with payment dates and the contract’s interest method is needed; this calculator’s total-interest figure assumes every scheduled payment is made as entered.

Frequently Asked Questions

How do I calculate a car payment?
Convert APR to a monthly rate by dividing the percentage by 1,200, multiply the loan term in years by 12, and use the fixed-payment formula shown above. The calculator performs those steps and rounds the monthly result to cents.

Does a car payment calculator include taxes and insurance?
Not by default. This calculator estimates principal and interest only. Costs included in the amount financed can be reflected by adding them to the loan amount, but recurring insurance and other ownership expenses are not calculated.

Why does a longer car loan have a lower monthly payment?
The principal is spread across more monthly installments. Since interest is charged over the repayment period, a longer term can also increase total interest when the principal and APR stay unchanged.

Is APR the same as the interest rate?
They are related but not necessarily identical. APR is an annualized measure of borrowing cost, while a contract’s interest rate is used to calculate interest on the balance. This simple calculator uses the entered APR as a nominal annual rate divided into monthly periods, so fees or other APR components may make a lender’s figures differ.

Why is my lender’s payment different from the estimate?
The amount financed, APR, payment dates, fees, rounding method, or final-payment adjustment may differ from the values or assumptions used here. Compare the calculator inputs with the lender’s payment schedule and disclosures.

This result is an estimate, and the lender’s disclosure gives the exact figures.

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2