How this calculator works
Car shopping is engineered around one number — the monthly payment — because it's the easiest thing to make look small. Stretch the loan long enough and almost any car "fits the budget," while the total you hand the lender quietly balloons. This calculator flips the focus to the numbers that actually decide whether a deal is good: how much you finance, how much of your payments are pure interest, and what the car truly costs once the loan is done.
It builds your amount financed from the price, sales tax, and fees, minus your down payment and trade-in equity — and if you owe more on a trade-in than it's worth, it rolls that negative equity in and flags it. Then it shows your payment, total interest, and a side-by-side term comparison so you can see exactly what a longer loan costs you.
The method
Sales tax is applied to the price less the trade-in value, which is how most states calculate it. Negative trade-in equity increases the amount financed.
- Amount financed: $35,000 + $2,100 tax + $500 fees − $5,000 =
$32,600. - At 60 months: about
$653/month, with$6,594in total interest. - At 84 months: the payment drops to
$500— but total interest is$9,402, about $2,800 more for the same car. - At 36 months: a higher
$1,014payment, but only$3,906in interest — less than half the long-term cost.
Acronyms used on this page
- APR
- Annual Percentage Rate
Buying smart
Two ideas keep car loans from becoming money pits. First, a classic guideline: 20/4/10 — put at least 20% down, finance for no more than 4 years, and keep total vehicle costs (payment plus insurance) under 10% of your income. Second, remember a car is a depreciating asset: it loses value every month, so the longer your loan, the longer you risk owing more than it's worth, especially with little money down. A bigger down payment and a shorter term cost more monthly but far less overall, and keep you on the right side of that line. If you're still deciding whether to buy at all, our lease-vs-buy tool compares financing against leasing and paying cash.
Frequently asked questions
How is a car payment calculated?
From the amount financed (price + tax + fees − down − trade-in equity), the APR, and the term. The balance is amortized, so each payment is interest on the balance plus principal. Longer terms lower the payment but raise total interest.
Is a longer term worth it?
It lowers the payment but costs much more interest and keeps you owing on a depreciating car longer. Going 60→84 months can add thousands. Many experts suggest 4 years or less.
What is negative equity?
Owing more than the car is worth ("upside down"). Rolled into a new loan on a trade-in, it raises the amount financed and your payment — a sign to slow down.
Should I put more money down?
Usually yes — it lowers the amount financed, the payment, and total interest, and reduces the chance of going underwater. The 20% down guideline exists for exactly this reason.