How to calculate auto loan
M = P × r ÷ (1 − (1 + r)⁻ⁿ)
Worked example. Your monthly car payment: $636 / month.
Example inputs — Auto price: $35,000; Loan term: 60 months; Interest rate: 7%; Cash incentives: $0.00; Down payment: $5,000; Trade-in value: $0.00; Amount owed on trade-in: $0.00; Sales tax state: Florida — 6%; Other fees: $0.00; Finance taxes and fees: Include in loan. Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
Payment depends on vehicle price less incentives, down payment and trade-in equity. Negative equity increases the loan. Choose whether modeled sales tax and fees are financed or paid upfront. The simplified tax base subtracts trade-in and incentives; actual state treatment can differ.
Using the auto loan estimate
A car payment starts with the amount financed, not just the sticker price. This tool adds modeled sales tax and subtracts your down payment and trade-in before calculating a fixed monthly installment. It helps compare financing offers on the same vehicle, or check how much a longer term changes the payment. A low payment can conceal a higher total borrowing cost, so read the financed amount and interest together before choosing an offer.
Step-by-step inputs
- Auto price. Use the purchase price before the sales tax entered in Advanced options. Do not use an already-financed total that includes that tax. Starting example: $35,000 .
- Loan term. Match the number of monthly installments in the offer. Five years means 60 payments, not 60 years. Starting example: 60 months .
- Interest rate. Use the quoted annual loan rate. The calculation applies it monthly and does not separately model lender fees. Starting example: 7% .
- Cash incentives. Replace the starting value with your own, keeping the displayed unit and period. Starting example: $0.00 .
- Down payment. Enter cash paid toward the purchase, separate from the trade-in value. Keep insurance and emergency cash outside this amount. Starting example: $5,000 .
- Trade-in value. Use a trade-in amount that will actually reduce the financing. If the old vehicle has a loan, an offer's gross trade value may overstate usable credit. Starting example: $0.00 .
- Amount owed on trade-in. Replace the starting value with your own, keeping the displayed unit and period. Starting example: $0.00 .
- Sales tax state. Replace the starting value with your own, keeping the displayed unit and period. Starting example: Florida — 6% .
- Other fees. Replace the starting value with your own, keeping the displayed unit and period. Starting example: $0.00 .
Worked example with the starting values
Using the starting inputs, the estimate is Your monthly car payment: $636 / month.
The starting scenario finances the price plus modeled tax, less cash down and trade-in. Interest is then charged on that financed balance over the selected term. The payment covers this loan only; owning and operating the car needs another monthly allowance.
- Sales tax
- $2,100
- Amount financed
- $32,100
- Total interest
- $6,037
- Total cost
- $43,137
Compare interest rate scenarios
The financed balance and term stay fixed, isolating the effect of the annual rate. These are scenarios, not available lending offers.
| Interest rate | Your monthly car payment |
|---|---|
| 5% | $606 / month |
| 7% | $636 / month |
| 9% | $666 / month |
Make a useful comparison
Compare terms at the same price, rate and down payment first. A longer repayment schedule spreads principal across more months, reducing the installment while generally adding interest. Then replace the rate with the actual quote for each term, because lenders need not offer the same rate on every schedule.
Look beyond the payment when evaluating affordability. Add insurance, fuel or charging, registration, maintenance and parking to a household budget. Keep enough cash for these expenses even if using more cash down would make the loan payment attractive.
Ask for an itemized out-the-door price and financing disclosure. Compare the model's financed balance with the contract balance. A difference may come from warranties, documentation fees, old-loan debt or a tax treatment that this simplified tool does not include.
Common mistakes to avoid
- Do not subtract a trade-in twice if the price already reflects it. Negative equity on an old loan is not a down payment; financing it increases the new debt.
- The total-cost figure is not a complete lifetime ownership estimate. Running costs, depreciation and resale proceeds are outside this model.
- A long term can leave debt outstanding when you want to replace the vehicle. A manageable payment alone does not tell you whether the car's resale value will cover the remaining balance.
Assumptions & limitations
- State picker applies the displayed state-level sales tax only. Local taxes, vehicle-specific rules, exemptions and fee taxation may differ; use a custom rate and confirm your dealer quote.
- This simplified tax base subtracts trade-in value and cash incentives. Those deductions are not allowed identically in every state or for every rebate type.
- Finance taxes and fees includes these modeled charges in principal; Pay upfront adds them to cash due instead.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Can I use an auto loan calculator for a used car?
Yes. Enter the used vehicle price, down payment, trade-in, rate and term. This model taxes the full vehicle price and omits dealer fees and existing trade-in debt, so adjust the financed amount or compare an itemized quote.
What's the ideal down payment for a car loan?
There is no universal ideal. Compare the payment, interest and risk of owing more than the car is worth while preserving emergency savings. A down payment reduces borrowing; lender requirements and vehicle depreciation vary.
Are auto loan calculators accurate?
They accurately model the entered fixed-rate installment terms, but may not reproduce a contract's daily interest, fees or rounding. This tool adds entered sales tax and subtracts down payment and trade-in; check the actual amount financed.
What is APR, and how does it affect my loan?
APR expresses an annual borrowing cost and can include certain fees. The payment engine uses a nominal annual interest rate divided by 12. When APR differs from the contract interest rate, use the contract rate for payment estimates and APR to compare loan costs.
Can I use an auto loan calculator for a lease?
No. Lease payments depend on residual value, depreciation, money factor, fees and taxes rather than repayment of a purchase loan. This tool models financed ownership, not leasing.
Is it better to choose a shorter or longer loan term?
At the same rate and balance, a shorter term raises the payment but lowers total interest. A longer term lowers the payment but may increase negative-equity risk. Compare actual quotes and total cost, not just monthly payment.
Do auto loan calculators consider my credit score?
This one does not. Enter the rate a lender offers or test illustrative rates. Credit can influence approval and pricing, but this calculator cannot determine either.
Why don't my calculator results match dealer quotes exactly?
Quotes may include documentation charges, add-ons, rebates, negative trade-in equity, different tax treatment or daily interest. Match the contract rate, term and itemized amount financed before comparing results.
Does the payment include car insurance?
No. It includes principal and modeled loan interest. Budget insurance and operating costs separately.
Does a trade-in always reduce sales tax?
Not in this model: tax is calculated on the full vehicle price. Use the dealer's itemized quote to check the rules for your purchase.