How an auto loan payment is worked out
An auto loan is a fixed-repayment loan with a car-specific twist: what you actually finance is rarely the sticker price. Start with the price, subtract your down payment, then subtract your trade-in's equity, what it's worth minus whatever you still owe on it. Add back tax and fees only if you choose to roll them into the loan rather than pay them at signing. What's left is the amount financed, and the same amortising formula used for any fixed loan turns that, an APR and a term into a monthly payment:
Run the calculator's own defaults through it: a $30,000 car, $5,000 down, a $3,000 trade-in with nothing owed on it, no tax or fees, at 6% APR over 60 months. The amount financed is $22,000, and the formula returns a monthly payment of $425.32. Over the full 60 months that's $25,519.20 paid back, $3,519.20 of it interest on top of the $22,000 financed. Every payment splits between interest on the balance still owed and a reduction of that balance, so the split shifts gradually from mostly interest towards mostly principal as the balance falls, the same as any other level-payment loan; the Loan Calculator covers that mechanic for borrowing in general, without the car-specific parts below.
Trade-in equity, and what negative equity actually costs
A trade-in only helps if it's worth more than what's left to pay on it. Equity is simply value minus what's owed: trade in a car worth $8,000 with a $5,000 payoff and $3,000 comes straight off the new loan, the same as cash. Owe more than it's worth, and the gap runs the other way. Trade in that same car with a $10,000 payoff instead of $5,000 and the $2,000 shortfall doesn't vanish, it gets added to what you finance on the new car, a rolled-in balance dealers usually call negative equity or being "upside down." You end up financing a car you no longer have alongside the one you just bought, paying interest on both. Carrying negative equity forward from loan to loan, trading in every few years before a car is ever paid off, is how that gap can grow rather than close.
Sales tax, and why the trade-in question matters
Sales tax on a car purchase is not a fixed national rule; it is set state by state, and so is the answer to whether a trade-in reduces what gets taxed. In the large majority of US states, the trade-in value is deducted from the price before tax is calculated, so a $35,000 car traded against a $12,000 vehicle is taxed on $23,000, not $35,000. A smaller number of states, California and Virginia among them, tax the full purchase price regardless of any trade-in. A few states cap the credit rather than removing it outright, and some charge no sales tax on vehicles at all. The toggle above defaults to taxing price minus trade-in, the more common rule, but only your own state's tax office or DMV gives the figure that will actually appear on the paperwork.
Fees, title, registration, documentation and similar dealer charges, are a flat add-on rather than a percentage, and unlike tax they rarely vary by choice of state rule, only by amount. Both tax and fees can usually either be paid in cash at signing or rolled into the loan itself; rolling them in raises the amount financed and the total interest paid on it, since you're now paying interest on the tax and the fees as well as the car, while paying upfront keeps the loan smaller at the cost of a bigger cheque on the day.
Why a longer term isn't automatically the better deal
Stretching the term lowers the monthly payment, because the same amount financed is spread across more months, and it raises the total interest, because a longer term leaves more months for interest to build on a balance that falls more slowly. The "Cost by loan term" table above runs the same amount financed and the same APR across five common terms, 36 through 84 months, so that trade-off is visible before a term gets picked rather than after the paperwork's signed. A longer term also drags out negative equity risk specifically: cars depreciate quickly in the first few years, and a loan that pays down slowly can leave you owing more than the car is worth for longer, which matters if the car is ever traded in, written off or sold before the loan is clear. Matching the term to how long the car is actually likely to be kept is a more useful anchor than simply picking whatever term gets the payment low enough.
Reading the results above
The donut splits the total cost into what's financed for the car itself, the interest charged on the loan, and tax plus fees, whether or not they were rolled in; the stats table alongside it lists every figure that fed the calculation, price through total cost, so nothing above is a black box. The line chart shows the loan balance falling from the amount financed to zero over the term, assuming every payment lands on schedule. None of it substitutes for the actual figures on a real finance offer, which can include add-ons, a different APR once the loan is underwritten, or a dealer fee this calculator doesn't know about.
Questions people ask
Should I finance through the dealer or a bank or credit union?
Whichever offers the lower APR for the same term, all else equal. Dealers can offer genuinely competitive promotional rates on some models, but they can also mark up a rate arranged through their finance partners, so getting a pre-approved rate from a bank or credit union first gives a real number to compare against, and sometimes room to negotiate the dealer's offer down to match or beat it.
Is it better to put more down or take a shorter term?
Both shrink the total interest paid, for the same underlying reason: less financed for less time. A bigger down payment also protects against negative equity from day one, since the loan starts smaller against a car that will depreciate regardless. A shorter term forces a higher monthly payment for the same amount financed, so the honest choice usually comes down to what the monthly budget can actually absorb, not which lever is "better" in the abstract.
Does my trade-in have to go towards this specific car?
No. A trade-in's value can be applied at the same dealer as a discount off any vehicle they sell, but there's no requirement to trade in at all. Selling a car privately usually nets more than a dealer trade-in offer, since the dealer needs margin to resell it, at the cost of the tax credit in the states that offer one and the convenience of a single transaction.
What credit score gets the best auto loan rate?
Lenders bracket rates by credit tier, and the gap between the top and bottom tiers on a car loan is typically several percentage points, sometimes more on a used car than a new one. There's no single universal cutoff, since it varies by lender, but checking your own score before shopping for finance, and shopping more than one lender once you have it, matters more than guessing at where any particular tier begins.
Can I pay off an auto loan early?
Most auto loans allow extra or early payments without penalty, but not all; a small number of contracts, more often subprime or "buy here pay here" financing, include a prepayment penalty or use a pre-computed interest method that reduces the benefit of paying early. The finance agreement itself is the only reliable source for what a specific loan allows, and it's worth checking before assuming an overpayment saves what it would on a standard loan.
Why is my actual quote different from this calculator?
This tool assumes a single fixed APR applied evenly across the term, with no add-ons beyond the tax and fees entered. A real finance offer can include GAP insurance, an extended warranty or other dealer add-ons rolled into the same monthly figure, a different APR once your credit is actually underwritten, or a dealer fee not accounted for here. Use the numbers on the actual finance agreement, not the advertised rate, before deciding.
These figures are estimates for a simple fixed-rate auto loan, not financial advice. What a lender or dealer actually offers depends on your credit, the specific vehicle, add-ons and their own underwriting, so check the finance agreement, or ask directly, before signing anything.