Calculate an estimated monthly auto loan payment by entering the amount financed, annual percentage rate (APR), and loan term. The calculator also estimates total interest using the displayed monthly payment; it does not include vehicle taxes, insurance, or other charges unless they are included in the amount financed.
Formula
The calculator uses the fixed-payment loan formula. It converts the annual APR to a monthly rate, then calculates the payment that repays the principal and interest over the selected number of monthly payments:
Payment = round(P × r ÷ [1 − (1 + r)−n], 2)
- P is the amount financed, in dollars.
- r is the monthly interest rate, calculated as APR ÷ 1,200. For example, 8% APR gives a monthly rate of 0.0066667.
- n is the number of monthly payments, calculated as loan term in years × 12.
- round(…, 2) rounds the monthly payment to the nearest cent.
Total interest is estimated as the rounded monthly payment multiplied by the number of payments, minus the amount financed: Total interest = payment × n − P. Since the monthly payment is rounded first, this total reflects that rounded payment and can differ slightly from a calculation using unrounded amounts.
Worked Example
Using the calculator’s default inputs—$20,000 financed, 8% APR, and a five-year term:
- Convert APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
- Calculate the number of monthly payments: 5 × 12 = 60.
- Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)−60] = $405.527…, which rounds to $405.53 per month.
- Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.
The payment and interest are estimates under the assumptions below. A lender’s payment schedule can differ if its calculation conventions, payment dates, or financed charges differ.
Assumptions
- The interest rate stays fixed for the full term.
- Payments are equal monthly payments, made at the end of each monthly period.
- Interest accrues monthly using APR divided by 12 (APR ÷ 1,200 as a decimal rate).
- The calculation excludes fees, taxes, insurance, optional products, and other charges unless they are already included in the loan amount entered.
What Amount Should You Enter?
Enter the amount actually financed, not necessarily the vehicle’s advertised price or the cash price. A useful starting calculation is the negotiated vehicle price plus any amounts added to the loan, minus the down payment and any trade-in credit applied to the purchase. The exact contract may include additional items, so use the lender’s stated amount financed when available.
For example, if a vehicle costs $24,000 and a buyer puts $4,000 down, the amount financed is not automatically $20,000: taxes, fees, a trade-in balance, or optional products may change the figure. This calculator cannot determine those items. Enter them as part of the loan amount only if they are included in the amount being financed.
How to Read and Use the Estimate
The monthly payment is the regular principal-and-interest amount implied by the three inputs. Total interest estimates how much interest is paid across all scheduled payments, assuming the payment is made on time and the loan follows the fixed-rate model. Neither number is a full ownership-cost estimate: fuel, maintenance, insurance, registration, and other expenses are outside this formula.
- Use the APR and term from a lender’s written quote or disclosure rather than guessing. Rates, fees, and contract terms vary; get the applicable figures directly from the lender.
- Check whether the quoted payment includes only principal and interest or also includes other financed charges.
- Compare estimates only when the loan amount, APR, and term are stated on the same basis.
- For a different down payment, trade-in amount, or financed add-on, update the loan amount before interpreting the result.
A longer term spreads repayment over more months and usually lowers the calculated monthly payment for the same principal and rate, while increasing the number of payments over which interest accrues. A shorter term does the reverse in this formula. This is a mathematical comparison, not a recommendation about which term to choose.
Common Calculation Mistakes and Limits
One frequent mistake is entering 8 for an 8% APR but treating the value as 8 in a decimal-rate formula. This calculator expects APR as a percentage, such as 8, and converts it internally by dividing by 1,200. Another is entering the vehicle price instead of the amount financed, or entering a term in months when the field requests years.
The formula models a fixed rate and equal monthly payments. It does not calculate a changing-rate loan, irregular payment schedule, balloon payment, skipped payment, late charge, or early payoff. It also does not model fees paid separately or show how a payment is split between principal and interest each month. If you make extra payments or the contract uses a different schedule, the actual balance and total interest will differ. Rounding the payment to cents can create a small difference from a lender’s final payment schedule, which may adjust the last payment.
Frequently Asked Questions
How do I calculate a car payment by hand?
Convert APR to a monthly decimal rate by dividing the percentage by 1,200, and multiply the number of years by 12 to get the payment count. Substitute those values and the amount financed into the fixed-payment formula shown above, then round the result to cents.
Does the auto loan payment include insurance and taxes?
Not by default. The result covers modeled principal and interest only. Taxes, insurance, and fees are excluded unless an amount is included in the loan principal you enter; recurring ownership costs are not calculated.
Why is my lender’s quoted payment different?
The amount financed, rate, term, payment timing, financed charges, and rounding may differ from your inputs or this estimate’s assumptions. Check the lender’s payment schedule and disclosure for the contract figures.
Does a longer car loan term reduce total interest?
Not under this fixed-rate model when the amount and APR stay the same. A longer term means more scheduled payments and generally more total interest, even though its calculated monthly payment is lower.
Can I use this calculator for a zero-interest loan?
This calculator requires an APR above zero because its formula divides by the monthly rate. For a true 0% fixed-rate loan with no other financed charges, the basic payment is the amount financed divided by the number of monthly payments; verify the contract’s terms with the lender.
This result is an estimate, and the lender’s disclosure gives the exact figures.
Related
Formula used
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
Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work
Method: the standard loan formula for this calculation, fixed rate and monthly compounding unless stated, rounded as each result states. Not financial advice; no lender, rate or product is recommended. See formulas and assumptions, the disclaimer or report an error.
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