calculate-loan

01 Loan payments

Auto Loan Payment Calculator: Estimate Monthly Costs

Calculator No. 01-6934 · Updated · Formula and assumptions shown below

Monthly payment $405.53
Total interest
$4,331.80
= Monthly payment × loan term × 12 − loan amount
Loan amount
$20,000
Input
Interest rate (APR)
8 %
Input
You enter
Loan amount ($), Interest rate (APR) (%), Loan term (years)
You get
Monthly payment ($), Total interest ($)
Rounding
2 dp

Estimate for education, not financial advice. The result follows from the numbers you enter and the formula shown. It is not a quote or an offer, and it does not include fees, taxes or insurance unless the calculator asks for them. Ask your lender for the exact figures.

An auto loan payment calculator estimates your fixed monthly principal-and-interest payment from the amount borrowed, APR, and loan term; it also estimates total interest. Enter the figures from a lender’s quote to see how the payment changes with the loan’s length and rate.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual percentage rate to a monthly rate, then calculates the payment that pays down the balance over the specified number of months.

Monthly payment: M = round[P × r ÷ (1 − (1 + r)−n), 2]

Total interest: I = (M × n) − P

  • P is the amount borrowed, in dollars.
  • APR is the annual percentage rate entered as a percentage.
  • r is the monthly rate, calculated as APR ÷ 1,200. For example, 8% APR gives r = 0.0066667 per month.
  • n is the number of monthly payments, calculated as years × 12.
  • M is the monthly principal-and-interest payment, in dollars, rounded to the nearest cent.
  • I is estimated total interest over the loan, in dollars. It uses the rounded monthly payment.

The formula assumes equal payments made monthly and a fixed rate. The APR is entered as an annual rate; it is not entered as a decimal. A rate of 8% is entered as 8, not 0.08.

Worked Example

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

  1. Convert the APR to a monthly rate: r = 8 ÷ 1,200 = 0.0066667.
  2. Convert the term to payments: n = 5 × 12 = 60 months.
  3. Substitute into the payment formula: M = round[20,000 × 0.0066667 ÷ (1 − (1 + 0.0066667)−60), 2] = $405.53 per month.
  4. Calculate total interest using the rounded payment: I = ($405.53 × 60) − $20,000 = $4,331.80.

The payment is an estimate of principal and interest, not a complete estimate of every cost associated with owning or financing a vehicle.

Assumptions

  • The interest rate is fixed for the full loan term.
  • Payments are equal, monthly, and made at the end of each monthly period.
  • Interest is calculated monthly using APR divided by 12.
  • Fees, taxes, insurance, add-on products, and other charges are not included unless they are included in the amount borrowed.

Using the Result for an Auto Loan

Enter the amount actually financed—not necessarily the vehicle’s advertised price. A down payment or trade-in may reduce the amount borrowed, while taxes, registration costs, optional products, and rolled-in fees may increase it. The lender’s loan documents show which charges are financed and the resulting principal.

Use the APR and term associated with the quote you are examining. The APR is a yearly borrowing-cost measure expressed as a percentage, but this calculator uses it as the nominal annual rate divided into monthly periods. Actual loan disclosures can include details or charges that this simplified calculation does not model. If the lender provides a payment schedule, compare the calculator’s estimate with that schedule rather than treating a small difference as an error in the quote.

The monthly payment and total interest answer different questions. The payment describes the scheduled monthly principal-and-interest amount. Total interest estimates the financing cost across all scheduled payments, excluding the principal borrowed. The calculator’s total interest is based on the payment rounded to cents, so its arithmetic follows the displayed monthly amount.

What Changes the Payment?

  • Amount financed: Borrowing more generally raises the payment and the amount of interest charged over the term, assuming the same APR and duration.
  • APR: A higher entered rate raises the scheduled payment for the same principal and term.
  • Loan term: Spreading repayment over more months generally lowers the monthly payment, but creates more payment periods in which interest can accrue. The total interest may therefore be higher even when the monthly figure is lower.

These are mathematical effects, not a recommendation about which loan structure to choose. Compare the full amount due and the documented terms, not only the monthly payment. A payment can look smaller simply because repayment extends over a longer period.

Common Calculation Limits and Mistakes

A frequent input mistake is using the vehicle price instead of the amount financed, or entering APR as a decimal. Another is treating the result as the total car cost: the calculator excludes running costs such as fuel and maintenance, and it does not calculate insurance premiums. The values needed for those expenses are separate from loan-payment arithmetic.

This formula applies to a conventional amortizing loan with a fixed rate and level monthly payments. It does not model a variable rate, irregular payment dates, skipped payments, a balloon payment, changing fees, or extra principal payments. Extra payments can alter the payoff timing and interest charged; this calculator assumes only the scheduled payment. If a lender’s contract uses different payment timing or includes financed charges, its disclosed schedule can differ from this estimate.

Rounding also matters. The monthly result is rounded to cents before total interest is calculated. A lender’s final payment may be adjusted by a small amount to clear the remaining balance, and exact figures depend on the contract’s schedule and calculations.

Frequently Asked Questions

How do I calculate an auto loan payment?
Use the amount financed, monthly interest rate (APR divided by 1,200), and number of monthly payments in the fixed-payment formula shown above. The calculator applies that formula and rounds the payment to cents.

Does the calculator include taxes and insurance?
No. It estimates principal and interest only. Include a charge in the calculation only if it is part of the amount financed; insurance and other costs are otherwise outside the formula.

Why does a longer auto loan have a lower monthly payment?
The principal is divided across more scheduled payment periods, which can lower each payment. More periods also mean interest can accrue for longer, so a lower payment does not necessarily mean lower total interest.

What loan amount should I enter?
Enter the principal the lender will finance. It may differ from the vehicle price because of a down payment, trade-in, taxes, fees, or other amounts included in the contract.

Why might my lender’s payment differ from this estimate?
The lender may use different payment dates, round or adjust the final payment, or include financed charges or contract terms not represented here. Check the lender’s payment schedule and disclosure for the exact figures.

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

Related

Formula used
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

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard loan formula for this calculation, fixed rate and monthly compounding unless stated, rounded as each result states. Not financial advice; no lender, rate or product is recommended. See formulas and assumptions, the disclaimer or report an error.

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