How to Use This Auto Loan Calculator
This calculator estimates your monthly car payment by factoring in the vehicle price, your down payment, any trade-in value, sales tax, interest rate, and loan term. Unlike a simple loan calculator, it accounts for the specific mechanics of auto financing in the US, where sales tax and trade-in credits directly affect the amount you actually finance.
How the Amount Financed Is Calculated
Most states calculate sales tax on the vehicle price after subtracting your trade-in value (though a handful of states tax the full purchase price regardless of trade-in — check your state's rules). This calculator applies that common approach: it subtracts your trade-in from the vehicle price to determine the taxable amount, applies your sales tax rate, then adds that tax back to the total. From there, it subtracts your down payment and trade-in value to arrive at your final loan amount:
Amount Financed = (Vehicle Price + Sales Tax) − Down Payment − Trade-In Value
That amount financed is then run through the standard amortization formula to calculate your fixed monthly payment over your chosen term.
New vs. Used Car Loan Rates
Interest rates on auto loans depend heavily on whether the vehicle is new or used. New car loans typically carry lower rates than used car loans because newer vehicles are considered lower-risk collateral — they depreciate more predictably and are less likely to need costly repairs during the loan term. Used car loan rates are typically higher, and the gap can be substantial for older or high-mileage vehicles. Our guides on new car financing and used car loans explain what to expect in more detail.
Why Loan Term Matters More Than It Seems
Auto loan terms have lengthened significantly over the years, with 72-month and even 84-month loans now common. While a longer term lowers your monthly payment, it also means you'll pay considerably more in total interest, and — because cars depreciate quickly — you're at much higher risk of being "underwater" (owing more than the car is worth) for a large portion of the loan. This matters if you want to sell or trade in the vehicle before the loan is paid off. Generally, shorter terms with higher monthly payments minimize total interest cost and reduce the risk of negative equity, provided the payment fits comfortably in your budget.
The Value of a Larger Down Payment
Putting more money down reduces the amount you need to finance, which lowers both your monthly payment and total interest paid. It also helps offset the rapid depreciation that occurs the moment a new car is driven off the lot, reducing the risk of owing more than the car's resale value. If you're financing a vehicle with little or no down payment, consider a shorter loan term if your budget allows, to avoid an extended period of negative equity.
How Trade-Ins Affect Your Loan
Trading in a vehicle can meaningfully reduce your loan amount and, in most states, your taxable purchase amount. However, if you still owe money on your trade-in, that remaining balance (negative equity) is often rolled into your new loan, which increases your amount financed rather than decreasing it. Always ask the dealer to show trade-in value, payoff amount, and resulting loan amount as separate line items so you understand exactly how the numbers work before signing.
Refinancing an Existing Auto Loan
If you already have an auto loan and interest rates have dropped, or your credit has improved since you originally financed the vehicle, refinancing could lower your monthly payment or total interest cost. Our guide on auto loan refinancing explains when refinancing makes sense and what to watch out for, including any prepayment penalties on your current loan.
Lease Buyouts Work Differently
If you're financing the purchase of a vehicle you currently lease rather than buying new or used from a dealer, the math is somewhat different since you're financing a pre-negotiated buyout price rather than a market purchase price. See our dedicated guide on lease buyout loans for details specific to that situation.
Preparing to Finance a Vehicle
Getting preapproved for an auto loan through a bank or credit union before visiting a dealership can give you a clear budget and negotiating leverage, since you'll know your rate and terms independent of dealer financing offers. Comparing your credit union or bank's rate against the dealer's financing offer — which may include manufacturer incentives — is one of the best ways to ensure you get competitive terms. If your credit is limited, our guide on credit builder loans covers ways to strengthen your profile before a major purchase.
Limitations of This Calculator
This tool provides an estimate based on the figures you enter and does not include dealer fees, documentation fees, title and registration costs, or gap insurance, all of which can add to your total out-of-pocket cost. Sales tax rules also vary by state — some tax the full purchase price regardless of trade-in, and local jurisdictions may add additional tax on top of the state rate. Always confirm final numbers with your lender and dealer's official documents before signing a purchase agreement.