Car Loan Comparison Calculator: Compare Monthly Payments

A car loan comparison calculator estimates the monthly payment and total interest for one fixed-rate auto loan from its amount, APR, and term. Enter the figures from a lender’s quote or a hypothetical offer to see the estimated cost; comparing multiple offers means running the calculator separately for each set of terms.

Formula

The calculator uses the standard level-payment formula for a fixed-rate loan with monthly payments:

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

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. APR is entered as a percentage per year.
• n is the number of monthly payments, calculated as loan term in years × 12.

Total interest is estimated as the rounded monthly payment multiplied by the number of payments, minus the amount borrowed: interest = payment × n − P. The payment is rounded to cents before the interest total is calculated, matching the calculator’s displayed results. Real lenders may calculate and disclose amounts differently because of payment dates, fees, or other contract details.

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: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 monthly payments.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. The monthly payment rounds to $405.53.
5. Total interest using the rounded payment is $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The interest rate stays fixed throughout the loan.
• Payments are equal, made monthly, and begin on a regular schedule.
• Interest is modelled monthly at APR ÷ 12.
• The estimate excludes fees, taxes, insurance, optional products, and other charges unless they are included in the amount borrowed.

How to Compare Car Loan Offers

For a useful comparison, enter the amount financed, APR, and term for each offer separately. Keep the amount borrowed the same when you want to isolate the effect of rate and term. If the offers finance different amounts—for example, because one includes an add-on or a different down payment—record that difference too. A lower monthly payment by itself does not show that one loan costs less overall.

• Amount financed: Use the loan principal shown in the offer, not automatically the vehicle’s advertised price. A down payment, trade-in credit, taxes, and fees can affect the amount financed.
• APR: Enter the APR stated in the quote, not a rate guessed from a monthly payment. Ask the lender for the exact figure and whether any charges are included in its calculation.
• Term: Enter the full repayment period. A longer term generally spreads repayment across more months, which can lower the scheduled payment while increasing the number of months interest may accrue.
• Payment and total interest: Review both outputs. Also compare any lender-provided total of payments and the amount due at signing, because this calculator does not include all contract costs.

For example, comparing a five-year offer with a seven-year offer at the same principal and APR can show why the longer offer may have a smaller monthly payment but more scheduled payments. The calculator does not decide which arrangement suits a person’s circumstances; it makes the arithmetic visible so the quoted terms can be examined.

What the Estimate Leaves Out

This tool calculates a single loan, not a side-by-side market search. To compare several offers, repeat the calculation with each offer’s actual inputs and keep a separate record of any differences in principal, fees, payment dates, or conditions. Obtain exact figures directly from the lender’s written disclosure rather than relying on an advertised example.

The displayed interest total is an estimate based on equal monthly payments and the stated assumptions. Actual contract totals can differ if the first payment is due on an unusual date, payments are not monthly, the rate is variable, payments change, or fees and optional products are financed. A payment quote can also appear lower because it includes a larger down payment, a final lump-sum payment, or a longer term. Check the repayment schedule and whether every amount is included before drawing conclusions.

Another common misconception is that a monthly payment comparison alone ranks loans by total cost. It does not: the term and principal matter, and charges outside the regular payment can change the amount paid. Conversely, a higher total-interest estimate does not describe every feature of an offer. Use the calculation as a consistent arithmetic comparison, then verify the full terms in the disclosure.

Common Comparison Mistakes

• Comparing monthly payments when the loan amounts or down payments differ.
• Entering a promotional or estimated rate instead of the APR in the actual offer.
• Ignoring term length, fees, or a final payment when assessing the total cost.
• Rounding APR or payment figures before entering them. Use the figures as quoted; the calculator rounds its payment output to cents.
• Treating the result as an approval, affordability decision, or guaranteed payoff schedule. It is only a mathematical estimate.

Frequently Asked Questions

How do I compare two car loans?
Run each offer using its amount financed, APR, and term. Compare the estimated monthly payment and interest, then check the written disclosures for fees, upfront amounts, and any final payment not represented by this calculation.

Does a lower monthly car payment mean a cheaper loan?
Not necessarily. A longer repayment term can reduce the scheduled monthly amount while increasing the number of payments and potentially the total interest. Compare the term and total contractual costs as well as the payment.

Should I enter the car price or the loan amount?
Enter the amount borrowed, or amount financed, from the offer. It can differ from the vehicle price because of down payment, trade-in credit, taxes, fees, or other amounts included in financing.

Does this calculator include taxes and fees?
No. It calculates payments and interest from the principal, APR, and term only. Include a charge in the loan amount only if the lender’s quoted principal finances it, and check the disclosure for costs due separately.

Why does my lender’s payment differ from this estimate?
The calculation assumes a fixed rate, regular monthly payments, and monthly interest based on APR ÷ 12. A lender’s schedule may reflect payment timing, fees, financed extras, rounding, or other contract terms not modelled here.

This result is an estimate, and 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 | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2