Auto Loan Payment Calculator: Estimate Monthly Costs

This auto loan calculator estimates your monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and loan term. Enter the figures from a lender’s offer to see the scheduled payment and the total interest implied by the calculation.

Formula

The calculator uses the standard fixed-payment loan formula. It first calculates the monthly payment, rounding that payment to the nearest cent, then subtracts the amount borrowed from all scheduled payments to estimate total interest.

• p is the amount financed, in dollars.
• apr is the annual percentage rate, entered as a percentage per year.
• r is the monthly rate as a decimal: apr ÷ 1200.
• n is the number of monthly payments: loan term in years × 12.
• pmt is the monthly payment in dollars: p × r ÷ [1 − (1 + r)⁻ⁿ].
• int is estimated total interest in dollars: pmt × n − p.

The input named “Interest rate (APR)” is used as a nominal annual rate divided into 12 monthly periods. APR figures can reflect costs differently depending on the lender’s disclosures; this calculator does not add fees or recalculate an APR from a quoted interest rate. Use the lender’s stated APR when modelling an offer.

Worked Example

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

1. Convert the APR to a monthly decimal rate: 8 ÷ 1200 = 0.0066667.
2. Find the number of monthly payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month, rounded to cents.
4. Calculate total scheduled payments using the rounded payment: $405.53 × 60 = $24,331.80.
5. Subtract the amount financed: $24,331.80 − $20,000 = $4,331.80 in estimated total interest.

Assumptions

• The interest rate stays fixed for the full term.
• Payments are made monthly, with the first payment one month after borrowing and subsequent payments at regular monthly intervals.
• Interest is modelled monthly using APR ÷ 12.
• The calculation excludes fees, taxes, insurance, add-ons, and any down payment or trade-in unless these are reflected in the amount financed.
• The total interest uses the displayed monthly payment rounded to the nearest cent for every payment.

What the Results Mean for an Auto Loan

The monthly payment is the amount implied by the entered principal, rate, and term under the formula’s assumptions. Total interest is the estimated cost of borrowing over all scheduled payments; it is not the vehicle’s full purchase cost. For example, a down payment reduces the amount that needs financing, while taxes or optional products included in a lender’s contract may increase it.

Comparing offers requires more than looking at the monthly payment. A longer term generally spreads repayment across more months and can lower the scheduled payment, but it may increase total interest. A shorter term usually means fewer payments and less time accruing interest, while the monthly payment may be higher. The calculator makes that trade-off visible when you enter different terms, without accounting for any lender-specific changes in rates or fees.

For instance, a $25,000 amount financed is not necessarily the vehicle’s sticker price. The financed amount may reflect a down payment, trade-in credit, taxes, fees, or products added to the contract. Check the contract’s amount financed before entering a figure; otherwise, the result may not match the quoted payment.

How to Use the Calculator and Compare Scenarios

Use figures that describe the same loan offer, and change one input at a time when you want to understand what drives the result:

• Enter the amount financed, not automatically the vehicle’s advertised price.
• Enter APR as a percentage: type 8 for 8%, not 0.08.
• Enter the term in years. A 60-month term is five years.
• Record the monthly payment and total interest, then repeat with a different term or amount to see the mathematical effect.
• Compare the calculator’s estimates with the lender’s payment schedule and disclosure, including any fees or other contract details.

When comparing two offers, hold the amount financed and term constant if your goal is to isolate the effect of different APRs. If the amount financed, payment timing, or included charges differ, the payment difference cannot be attributed to APR alone. The quoted payment may also reflect rounding or terms not represented by this simple model.

Limits and Common Mistakes

This is a fixed-rate, level-payment estimate, not a complete vehicle ownership budget or a lender approval estimate. It does not calculate insurance, fuel, maintenance, registration costs, or the vehicle’s future value. It also does not model a changing rate, irregular payment dates, a balloon payment, skipped payments, or an early payoff. For a loan with fees financed into the balance, include them in the amount financed if the contract does so; do not add them again as a separate interest amount.

A frequent mistake is treating the monthly payment as the total cost. Multiply it by the number of payments and add any costs excluded from the model to understand the broader outlay. Another is entering the APR as a decimal rather than a percentage. Finally, displayed cents can create small differences versus a lender’s schedule: lenders may calculate interest using specific dates, daily balances, or other contract conventions.

Frequently Asked Questions

Does this calculator tell me what APR a lender will offer?
No. APR is an input. The result estimates payments for the rate you enter; it does not predict an offer, approval, or lender decision. Get the applicable figures from the lender.

Should I enter the car’s price or the amount financed?
Enter the amount financed shown in the loan documents or quote. It may differ from the vehicle price because of a down payment, trade-in, taxes, fees, or other items.

Why can a longer loan term have more total interest?
It schedules payments over more months, so the balance generally accrues interest for longer. The actual result depends on the entered amount, APR, and term.

Does the payment include insurance and taxes?
No. The calculation covers principal and interest under its assumptions. It excludes insurance, taxes, fees, and other costs unless they are included in the amount financed.

Why is my lender’s payment different?
The lender’s figures may include fees or products, use different payment dates or rounding, or reflect loan details not entered here. Compare the contract terms and ask the lender to explain the calculation.

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

Related

• Amortization Schedule With Annual Totals Calculator
• Amortization Schedule Using Payment Amount
• Amortization Schedule Spreadsheet: Payment and Interest

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 | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2