Car Loan Monthly Payment Calculator and Formula

This car loan monthly payment calculator estimates the fixed monthly principal-and-interest payment from the amount borrowed, APR, and loan term. Enter those three figures to see the payment and estimated total interest; the result does not include vehicle taxes, fees, or insurance.

Formula

The calculator uses the standard fixed-payment loan formula:

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

• P is the amount financed, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200.
• n is the number of monthly payments: loan term in years × 12.
• Payment is the monthly principal-and-interest amount, rounded to the nearest cent.

Estimated total interest is the rounded monthly payment multiplied by the number of payments, minus the original loan amount: interest = payment × n − P. Using the rounded payment here makes the displayed total match the payment used in the calculation; an actual lender’s final installment can differ slightly because of payment dates and rounding.

Worked Example

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

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1,200 = 0.0066667.
2. Find the number of monthly payments: n = 5 × 12 = 60.
3. Substitute the values: payment = 20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. Round the result to cents: estimated monthly payment = $405.53.
5. Estimate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The APR is fixed for the entire loan term.
• Payments are equal monthly amounts and are treated as made at the end of each monthly period.
• Interest compounds monthly using APR ÷ 12.
• The estimate excludes fees, taxes, insurance, and other charges. These are not calculator inputs.

What the Monthly Payment Includes

A standard installment payment covers both interest and principal. Interest is calculated on the remaining balance, so at the beginning of a level-payment loan a larger share of each payment generally goes to interest. As the balance declines, the interest portion usually shrinks and more of the payment reduces principal.

The vehicle’s advertised price is not necessarily the amount to enter as the loan amount. The financed amount can reflect a down payment, trade-in value, taxes, fees, optional products, and any balance carried over from another vehicle loan. For an estimate, use the amount you expect to borrow—not the vehicle price before those adjustments. Ask the lender for its actual amount financed and APR before relying on a payment figure.

How to Use and Interpret the Estimate

Enter the principal in dollars, the APR as a percentage per year, and the term in years. For example, enter 8 for 8%, not 0.08. The result is the scheduled principal-and-interest payment under the formula’s assumptions; it is not a complete monthly vehicle budget.

To understand the overall borrowing cost, read the payment alongside the total-interest estimate. A longer term spreads repayment over more months and can lower the scheduled payment, but it also means more periods in which interest can accrue. A shorter term has fewer payments, while the required monthly amount may be higher. The calculator holds the loan amount and APR constant so you can see how its assumptions affect the arithmetic; it does not determine which term suits a person.

For a fuller ownership budget, consider expenses the formula leaves out, such as insurance, fuel, maintenance, registration, and parking. Some charges may be paid upfront, while others recur. The lender’s loan disclosure or payment schedule is the source for the exact contractual figures and payment dates.

Common Sources of Difference

• Using the wrong principal: The amount financed may differ from the sticker price after a down payment, trade-in, added charges, or other adjustments.
• Confusing APR with a monthly rate: The calculator converts annual percentage APR to a monthly decimal by dividing by 1,200. Do not enter a monthly percentage in the APR field.
• Leaving out costs: A payment estimate from this formula does not automatically include taxes, insurance, or fees, even if some are included in a particular loan agreement.
• Rounding and timing: The calculator rounds the payment to cents for the total-interest calculation. A lender may use exact dates, daily interest, or a final payment adjusted for rounding, so its schedule can differ.
• Variable terms or extra payments: The formula assumes a fixed APR and the same scheduled payment each month. It does not model rate changes, skipped or late payments, or additional principal payments.

Frequently Asked Questions

How do I calculate a car loan monthly payment?
Convert the APR to a monthly decimal by dividing it by 1,200, convert the term to months, then apply the fixed-payment formula shown above. This calculator performs those steps and rounds the payment to cents.

Does a car loan payment include insurance or taxes?
Not in this estimate. It calculates principal and interest only. Taxes, insurance, and fees may be handled separately or included in a particular financing arrangement, so check the lender’s figures and your vehicle costs.

Why is my lender’s payment different from this estimate?
The amount financed, APR, term, payment dates, fees, and rounding may differ from the figures entered here. The calculator also assumes monthly compounding and excludes charges that are not inputs. Compare the same loan amount, APR, term, and included costs.

Does a longer car loan term reduce total interest?
Not necessarily. It can spread repayment across more months and lower the scheduled payment, while the longer repayment period can increase total interest when the other inputs are held constant. The calculator estimates the effect for the entered APR and principal.

Can I use this calculator for a used car loan?
Yes. The formula works for a fixed-rate installment loan regardless of whether the vehicle is new or used. Enter the amount financed, APR, and term that apply to the loan being estimated.

This result is an estimate; 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