The price on the windscreen isn't what you finance
Every car buyer has had this moment: you agree on $35,000, then the paperwork says you're financing $37,600. Nothing shady happened — sales tax and fees got added, and most online calculators quietly ignore both.
On a $35,000 car in a 6% sales-tax state with $600 in dealer and registration fees, that's $2,700 of extra cost before you've driven anywhere. This calculator adds it in by default, then subtracts your down payment and trade-in, so the "amount financed" you see is the number the lender will actually use.
How the math works
Monthly payment = P × [ r(1 + r)n ] ÷ [ (1 + r)n − 1 ]
Sales tax is applied to the price after the trade-in in most states — a real saving worth knowing about before you sell your old car privately.
The trade-in tax credit almost nobody mentions
If your state taxes (price − trade-in), a $5,000 trade-in at 7% tax saves you $350 instantly. Selling that car privately might get you $5,800 — but after losing the tax credit you're only $450 ahead for all that hassle. Run both numbers before deciding.
Why long loans cost so much more
Stretching a loan from 48 to 72 months feels harmless because the monthly payment drops. Change the term buttons above and watch the total interest line instead — it usually jumps by thousands. Meanwhile the car keeps losing value, so for the first few years you owe more than you could sell it for.
My honest rule of thumb: if the car only fits your budget at 72 or 84 months, it's not really in your budget. A cheaper car at 48 months costs less and puts you back in positive equity years sooner.
Before you sign
- Get pre-approved elsewhere first. Walk in with a rate from your bank or credit union — then dealer financing has to beat it, not set it.
- Negotiate the price, not the payment. "What monthly payment do you want?" is how a long term gets slipped in.
- Check the APR, not the interest rate. APR includes required fees; the headline rate may not.
- Put down 10–20%. It's the cheapest protection against negative equity.
If a personal loan is your alternative — for a private-party sale, for example — compare it with the personal loan calculator, which also shows the true APR once origination fees are counted.
Frequently asked questions
How is a car payment calculated?
The amount financed is the vehicle price plus sales tax and fees, minus your down payment and trade-in value. That amount is run through the standard amortizing loan formula using your APR and term length to give a fixed monthly payment.
Does a trade-in reduce sales tax?
In most US states, yes. Sales tax is charged on the price after the trade-in is deducted, so trading a $5,000 car in a 7% tax state saves $350 in tax. A handful of states tax the full price regardless — check your state's rule, because it changes whether trading in or selling privately is the better deal.
Is a 72 or 84 month car loan a bad idea?
Usually yes. Longer terms lower the monthly payment but sharply increase total interest, and cars depreciate faster than these loans amortize — meaning you owe more than the car is worth for years. If you can only afford the car at 72+ months, that is usually a sign the car is too expensive.
What is negative equity or being underwater?
It means your loan balance is higher than the car's market value. It happens with small down payments and long terms. If the car is totaled or you want to sell, you must pay the difference out of pocket — which is why gap insurance exists.
Should I take dealer financing or a bank loan?
Get pre-approved by a bank or credit union first, then let the dealer try to beat that rate. Dealers can offer excellent promotional rates on new cars, but they can also mark up the rate they got from the lender. Having an approved offer in hand is what protects you.