Car Loan Total Cost Calculator and Formula

This calculator estimates a car loan’s monthly payment and total interest from the amount financed, APR, and loan term. Enter the loan principal, annual percentage rate, and term in years; the results show the scheduled payment and interest, but not the vehicle’s full ownership cost.

Formula

The calculator uses the standard fixed-payment, fully amortizing loan formula. It first finds the monthly payment, rounded to the nearest cent, then subtracts the amount borrowed from the sum of all scheduled payments to estimate total interest.

• p = amount financed, in dollars.
• apr = annual percentage rate, entered as a percentage per year.
• r = monthly rate as a decimal: apr ÷ 1,200.
• n = number of monthly payments: years × 12.
• pmt = monthly payment in dollars: round[p × r ÷ (1 − (1 + r)⁻ⁿ), 2].
• int = estimated total interest in dollars: pmt × n − p.

The second result uses the rounded payment, so it reflects the repeated cent-rounded payment shown by the calculator. A lender may adjust the final payment slightly to clear a remaining balance, and its disclosure is the source for the exact schedule.

Worked Example

Using the calculator’s default inputs—$20,000 financed, 8% APR, and five years—the loan has 60 monthly payments. The monthly rate is 8 ÷ 1,200 = 0.0066667.

1. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. The unrounded result is approximately $405.53; rounded to cents, the monthly payment is $405.53.
3. Multiply the displayed payment by the number of payments: $405.53 × 60 = $24,331.80.
4. Subtract the original amount financed: $24,331.80 − $20,000 = $4,331.80 total interest.

These figures describe scheduled principal and interest only. The total of payments is $24,331.80 in this example; the vehicle’s complete cost can be higher once upfront charges and ongoing ownership expenses are included.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, made monthly, and paid at the end of each monthly period.
• Interest accrues monthly at APR ÷ 12 (the APR entered as a percentage is divided by 1,200 to get a decimal monthly rate).
• The estimate excludes fees, taxes, insurance, maintenance, fuel, and other ownership expenses; none is an input.

What “Car Loan Total Cost” Can Mean

People use “total cost” to mean different things. For the calculator, the related figures are the scheduled monthly payment and total interest. The sum of payments equals the amount financed plus interest. It is not necessarily the vehicle’s out-the-door price or the full amount a driver spends over the time they own the car.

For a broader comparison, separate the figures into three groups:

• Amount due to buy the vehicle: negotiated vehicle price plus applicable taxes and charges, less any down payment or trade-in value credited toward the purchase.
• Loan costs: principal and interest paid over the schedule, plus any financing charges not already included in the amount financed.
• Ownership costs: expenses such as insurance, fuel, upkeep, repairs, and registration, which are separate from the loan payment and vary with the vehicle and its use.

Do not add a fee twice. For example, if a fee is rolled into the amount financed, it is already part of the principal used in the payment calculation. If paid upfront instead, it is not part of this calculator’s loan amount.

How the Amount Financed Changes the Result

The loan amount is not always the advertised vehicle price. A down payment or trade-in credit can reduce the amount borrowed, while eligible charges added to the loan can increase it. A deposit, trade-in, or other credit should be treated according to how it appears in the lender’s itemized figures, rather than assumed to reduce the principal by a particular amount.

For example, a quoted $25,000 vehicle does not automatically mean the calculator’s input should be $25,000. The amount financed is the principal actually borrowed under the proposed terms. Check the itemized purchase figures and financing disclosure for that number, and confirm whether optional products or charges are included.

Term, APR, and Comparing Estimates

With the same principal and APR, a longer term generally lowers the scheduled monthly payment because repayment is spread over more months. It also gives interest more time to accrue, so total interest is generally higher. A shorter term usually produces a higher payment and less time for interest to accumulate. The calculator makes this tradeoff visible without determining whether a payment fits anyone’s circumstances.

APR is an annualized rate used here as the input for the monthly-interest calculation. The calculator assumes the entered APR applies throughout the term and does not model a changing rate, irregular payments, or lender-specific rounding practices. Use the actual proposed APR and term from the lender rather than treating the default 8% example as a market quote.

When comparing written estimates, compare the same principal, APR, term, payment frequency, and included charges. A lower monthly payment on its own does not establish a lower total cost: it may reflect a longer term, a different amount financed, or charges handled differently. Review the full payment schedule and disclosure, not just one number.

Common Mistakes and Limits

• Confusing APR with a monthly percentage: enter APR as a yearly percentage, such as 8, not 0.08. The formula converts it to a monthly decimal.
• Using the vehicle price as principal without checking: the amount financed can differ because of credits and charges.
• Calling total interest the total cost: interest is only the cost of borrowing in this estimate; it excludes principal and ownership expenses.
• Ignoring cent rounding: the displayed payment is rounded to cents before the total interest is calculated. A real final installment may differ slightly.

The formula is intended for a conventional fixed-rate loan with level monthly payments and full repayment over the stated term. It does not determine taxes or fees, quote insurance, account for a balloon payment, or model extra payments and early payoff. For those cases, use the actual written schedule or a calculator with the relevant inputs.

Frequently Asked Questions

How do I calculate the total interest on a car loan?
Multiply the scheduled monthly payment by the number of monthly payments, then subtract the amount financed. This calculator uses the payment rounded to cents for that estimate.

Does a car loan payment include insurance?
Not in this calculator. The payment covers estimated principal and interest only; insurance is a separate ownership expense unless a particular agreement explicitly treats a charge differently.

Does a longer car loan cost more overall?
For the same principal and APR, a longer term generally means more total interest because the balance is repaid over more months, even though the scheduled payment is generally lower.

Should I enter the car price or the amount financed?
Enter the amount actually borrowed. Check the itemized financing figures to see how down-payment credits, trade-in credits, and any charges added to the loan affect that amount.

Why might my lender’s total differ from this estimate?
The calculator assumes fixed-rate monthly payments and excludes fees and other costs. The lender may use specific payment dates, rounding, or a final-payment adjustment; consult the lender’s disclosure for its exact figures.

This result is an estimate for educational purposes; 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