How U.S. auto loans are really calculated
Dealerships often quote a payment before tax. In most states you still owe sales tax on the vehicle. Many states tax the price minus trade-in; this calculator uses that common pattern. Oregon, New Hampshire, Delaware, and Montana have no statewide sales tax — pick those states and watch the tax line drop to zero (local fees can still exist).
A longer term lowers the monthly number and raises lifetime interest. Use the 36 / 48 / 60 / 72 chips to see that trade-off in the doughnut, not just the payment. Negative equity shows up faster on a long term if the car depreciates while you still owe tax and fees that were rolled in.
If you already know the payment you can live with, use car affordability to work backward to a price ceiling. This page is for when you have a vehicle price and need the monthly number. Neither page is a credit decision — dealers and banks use your credit file, not this form.