Auto Loan Calculator with Trade-In and Sales Tax
Dealers love confusing the four numbers — price, trade-in, down payment, and monthly payment. This guide breaks them apart so you can see what you're actually paying for the car versus the financing.
Use the calculator
Auto Loan Calculator
Step-by-step
- 1
Negotiate price first, in isolation
Agree on the out-the-door price of the car before mentioning trade-in or financing. Mixing them lets the dealer hide adjustments.
- 2
Apply trade-in to taxable amount
In most states, trade-in reduces the price you pay sales tax on. Selling separately on Carvana/Carmax often nets more, but you pay tax on the full new-car price.
- 3
Calculate sales tax
State + local typically 5-9.5%. The Auto Loan Calculator factors this in. On a $35k car at 8% tax, that's $2,800 added to the loan unless you pay it cash.
- 4
Set down payment
20% down is the classic rule. Less is fine for cars under warranty; avoid 0% down on used cars where you might owe more than the car is worth.
- 5
Choose loan term realistically
60 months is standard. 72-84 months reduces monthly payment but means you owe more than the car is worth for years. Avoid >60 months unless cash flow is critical.
💡 Tips
- Get pre-approved through your credit union before shopping. Dealer financing often marks up the rate 1-3% as profit.
- Trade-in offers below 80% of KBB private-party value are usually too low. Compare with Carvana / CarMax instant offers.
- Add taxes, fees, and any negative equity from a previous loan into your loan calculator inputs to see the real picture.
FAQ
Should I roll negative equity into a new loan?
Strongly avoid. You start the new loan already underwater. Pay it off separately or wait to trade until equity recovers.
Is gap insurance worth it?
Yes if you put little down or financed >60 months. It pays the difference if the car is totaled while you owe more than it's worth.
How does APR differ from interest rate?
APR includes fees (origination, doc fees) on top of the rate. Always compare APR, not the rate, when shopping lenders.