Car Cost Comparison Calculator: Compare Loan Payments

This car cost comparison calculator estimates the monthly payment and total interest for a fixed-rate auto loan using the amount financed, APR, and term you enter. It shows the payment first, then the interest paid over the full term; it does not compare vehicle prices, fuel, insurance, or maintenance.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual percentage rate (APR) into a monthly rate, calculates the payment needed to repay the balance over the selected number of months, rounds that payment to cents, and subtracts the amount borrowed from the total of the scheduled payments to estimate interest.

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

Total interest: I = M × n − P

• P is the amount financed, in dollars.
• APR is the annual percentage rate entered as a percent.
• r is the monthly rate, calculated as APR ÷ 1,200.
• n is the number of monthly payments, calculated as loan term in years × 12.
• M is the monthly payment in dollars, rounded to the nearest cent.
• I is estimated total interest in dollars, based on the rounded monthly payment.

The formula assumes equal payments and a constant rate. APR is not entered as a decimal: for example, enter 8 for 8%, and the formula converts it to a monthly decimal rate of 0.08 ÷ 12.

Worked Example

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

1. Convert the term to payments: n = 5 × 12 = 60 months.
2. Convert the APR to a monthly rate: r = 8 ÷ 1,200 = 0.0066667.
3. Apply the payment formula: M = round[20,000 × 0.0066667 ÷ (1 − (1.0066667)⁻⁶⁰), 2] = $405.53 per month.
4. Calculate the total of the rounded payments: $405.53 × 60 = $24,331.80.
5. Subtract the amount financed: $24,331.80 − $20,000 = $4,331.80 in estimated interest.

These figures are mathematical estimates. A lender’s payment schedule can differ because of payment dates, rounding methods, fees, or other contract details.

Assumptions

• The APR stays fixed throughout the loan.
• Payments are equal, made monthly, and begin on schedule; the model does not account for a different first-payment date.
• Interest is treated as compounding monthly at APR ÷ 12.
• The amount financed is treated as the entire starting balance. The calculation excludes fees, taxes, insurance, optional products, down-payment effects beyond reducing the amount financed, and any separate charges.
• The loan is repaid with the scheduled payments, without extra payments, skipped payments, or a balloon payment.

How to Compare Car Loan Costs

For a useful comparison, calculate each loan using the amount actually financed, its quoted APR, and the same repayment period where possible. A vehicle’s advertised price is not necessarily the amount borrowed: a down payment may reduce it, while taxes, fees, add-ons, and any balance carried from another loan may change it. Ask for the lender’s amount-financed figure and use that as the calculator input.

To compare two offers, note both the monthly payment and total interest. A longer term commonly lowers the required payment for a given balance and rate because repayment is spread across more months, but it also creates more payment periods. This calculator makes that trade-off visible when you enter different terms. A lower payment alone does not establish that two offers have the same overall cost.

For example, comparing a five-year offer with a seven-year offer requires entering each offer’s actual APR and term. Do not assume that a longer term has the same APR, or that an advertised payment includes the same amount financed. The calculator isolates loan arithmetic; it cannot establish which vehicle or offer suits a person’s circumstances.

What This Comparison Leaves Out

Car ownership costs extend beyond the loan. Fuel or electricity, insurance, maintenance, repairs, registration, parking, and depreciation may all affect the overall cost of owning a vehicle. Those costs vary by vehicle, location, usage, and time, and are not inputs here. To compare ownership costs, gather separate estimates for each vehicle and keep them distinct from the loan’s principal and interest.

Likewise, a down payment is not itself interest savings in this calculator. It matters only insofar as it changes the amount financed. If a vehicle costs $25,000 and $5,000 is paid upfront, the loan balance might be based on $20,000 before any additional financed charges; use the actual amount shown in the loan disclosure rather than assuming that example matches a particular deal.

Common Calculation Mistakes and Limits

• Entering APR incorrectly: Enter 8 for 8%, not 0.08. The calculator performs the percent conversion.
• Using the sticker price as the loan balance: The amount financed can differ from the vehicle’s price. Check the figures supplied for the specific transaction.
• Comparing unlike terms: Different repayment periods change both monthly payments and total interest. Record the APR and term alongside each result.
• Reading interest as the full cost: Total interest is not the total paid for the car. It excludes the principal and costs outside the modeled loan.
• Expecting exact contract figures: The estimate rounds the monthly payment to cents and assumes regular monthly timing. A lender may use its own schedule and rounding.

The formula models a conventional fixed-rate installment loan with level monthly payments. It does not calculate a variable-rate loan, lease, balloon payment, payoff quote, or a schedule with extra payments. The APR and other loan terms are inputs, not market quotations; obtain the actual figures from the lender and check what charges are included.

Frequently Asked Questions

How do I compare car loan payments?
Enter each offer’s amount financed, APR, and term, then compare both the monthly payment and estimated total interest. Make sure the inputs describe comparable loans.

Does a longer car loan always cost more?
Not in every possible comparison, because the APR and amount financed may differ. For the same amount and APR, a longer term generally means more scheduled payments and more total interest, even though the monthly payment is lower.

Is total interest the same as the total car cost?
No. Total interest is the estimated borrowing charge above the amount financed. It does not include principal, vehicle running costs, or excluded transaction charges.

Should I enter the car’s price or the amount financed?
Enter the amount financed shown for the loan. It may be different from the vehicle price because of a down payment or amounts added to the loan.

Why might my lender’s payment differ?
The loan may have a different financed balance, APR, payment date, payment count, or rounding convention. Fees or other contract terms can also affect the disclosed figures.

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

Related

• How to Balance a T Account: Steps and Examples
• Beginning Balance: How to Calculate It
• How Minimum Balance Is Calculated

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