Car Loan Calculator

Amount financed = price + sales tax - down payment - trade-in equity, where equity is the trade value less anything still owed on it. Payment = the standard amortized formula on that amount, at the monthly rate, over the number of months.

Does a trade-in reduce the sales tax?

In most states, yes: tax is charged on the price minus the trade-in. That makes a trade worth slightly more than the same amount in cash. A few states tax the full price, so check locally.

Is a 72 or 84 month car loan a bad idea?

It lowers the payment and raises everything else. The car depreciates faster than the loan pays down, so you spend years owing more than it is worth, and a write-off in that window is expensive.

How much should I put down?

Twenty percent is the usual rule, and it exists to keep you above water as the car depreciates. Less than ten percent, with a long term, nearly always means negative equity within a year.