Car Loan Comparison Calculator: Compare Payments

A car loan comparison calculator estimates the monthly payment and total interest for a fixed-rate auto loan from its amount, APR, and term. Enter the figures for a proposed loan to see the estimated cost; the calculation uses a standard level-payment formula and does not include fees or vehicle expenses.

Formula

The calculator first converts the annual percentage rate (APR) to a monthly rate, then applies the fixed-payment loan formula:

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

Total interest = (monthly payment × n) − P

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. For an 8% APR, r = 0.08 ÷ 12.
• n is the number of monthly payments, calculated as loan term in years × 12.
• APR is entered as a percentage per year, not a decimal: enter 8 for 8%.

The payment is rounded to the nearest cent before total interest is calculated. This reflects the calculator’s stated payment-rounding convention; an actual lender’s final schedule can differ slightly because of payment dates, daily interest, rounding, and contract details.

Worked Example

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

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

Under these assumptions, the estimated payment is $405.53 per month and estimated total interest is $4,331.80. The total of the 60 rounded payments is $24,331.80, including the original $20,000 principal.

Assumptions

• The interest rate is fixed for the full loan term.
• Payments are equal, made monthly, and treated as occurring at the end of each period.
• Interest is modelled monthly using APR divided by 12.
• The estimate excludes lender fees, taxes, insurance, add-ons, and other vehicle or loan costs; none is entered as a calculator input.

How to Compare Car Loan Estimates

For a useful comparison, enter the same amount financed for each offer, along with each offer’s quoted APR and term. The amount financed may differ from a vehicle’s advertised price: a down payment or trade-in can reduce it, while items included in the loan can increase it. Use the amount shown in the lender’s written estimate or disclosure rather than assuming the sticker price is the loan amount.

Compare the monthly payment alongside total interest and the length of repayment. A longer term generally spreads principal repayment across more months, which can reduce the scheduled payment while increasing the number of periods in which interest accrues. The calculator helps show this arithmetic; it does not account for vehicle depreciation, maintenance, or whether a particular payment fits an individual budget.

• Keep the loan amount constant when isolating the effects of APR or term.
• Use the quoted APR for the particular offer, not a promotional or hypothetical rate.
• Check whether the quoted amount includes fees, optional products, or other financed items.
• Compare the lender’s disclosed payment schedule with the calculator’s estimate before relying on a figure.

When the Estimate May Differ

This is a standard amortization calculation, not a complete contract model. It assumes a fixed rate and regular monthly payments. Some contracts calculate interest using exact days between payments, and the first payment date or payment timing can affect interest. A final payment may also be adjusted for rounding. If the contract has a variable rate, irregular payments, a balloon payment, or a separate final amount, this calculator does not model those features.

Fees and taxes can also affect the actual amount borrowed or paid. If a charge is financed, it may increase the principal; if paid separately, it may not appear in the monthly loan payment. Insurance, fuel, registration, maintenance, and other ownership costs are outside the calculation. Ask the lender for a written breakdown of the financed amount, payment, APR, and total payments when comparing figures.

Common Input Mistakes and Limits

• Entering APR as a decimal: Type 8 for 8%, not 0.08. The calculator converts the percentage to a monthly decimal rate.
• Using the wrong principal: Enter the amount financed, not automatically the vehicle’s purchase price.
• Mixing payment frequencies: This calculator assumes monthly payments. It does not calculate weekly or biweekly schedules.
• Rounding too early: The formula rounds the monthly payment to cents and then uses that rounded amount for total interest. A lender may use its own schedule and rounding method.
• Assuming approval or a quoted rate: The calculator cannot determine whether a lender will offer a particular APR, amount, or term. Obtain actual figures directly from the lender.

The interest output is the estimated interest over the full scheduled term, not the total cost of owning the car. It also assumes every scheduled payment is made as specified and does not model extra payments or early payoff.

Frequently Asked Questions

How do I compare two car loans with different terms?
Enter each loan’s amount financed, APR, and term separately. Review both the estimated monthly payment and total interest; a lower payment by itself does not show the full cost or repayment duration.

Does a car loan calculator include a down payment?
Not directly. The down payment matters only insofar as it changes the amount financed. Enter the loan principal after accounting for the down payment, trade-in, and any amounts added to the loan.

Why is my lender’s payment different from this result?
The lender may use different payment dates, daily-interest calculations, fees, financed add-ons, or rounding. Check that the principal, APR, and term match, then compare against the lender’s written payment schedule.

Does a longer car loan term reduce total interest?
Not necessarily. A longer term can lower the scheduled monthly payment by spreading repayment over more months, but interest may accrue for longer. The calculator estimates the total under its fixed-rate assumptions.

Can I use this calculator for a variable-rate loan?
It can provide an estimate only if you treat the entered APR as fixed throughout the term. It cannot project rate changes or the payment adjustments that may follow them.

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