The monthly payment is the last number, not the first.
A dealership quote is a stack of numbers that are easy to mix up: price, tax, fees, payment, and a tire size if you are already planning wheels. The calculators here split that stack on purpose. Use them in this order.
The out-the-door calculator takes the price, subtracts the trade-in, applies the sales-tax rate you type, and adds doc and title fees. On a $32,000 car with a $4,000 trade, a 6% rate, a $500 doc fee, and $250 of registration, the total is $30,430. Move the rate to 8%, which is what a Philadelphia buyer should type on top of Pennsylvania’s 6% statewide rate, and the same car is $30,990. The $560 is tax, not a negotiating trick. Statewide rates are summarized by the Tax Foundation and, for Pennsylvania, by the Department of Revenue. County add-ons are your job to type.
The page subtracts the trade-in before tax in every state. That is right for Pennsylvania and wrong for states that tax the full price. If you are in one of those, zero the trade-in for the tax line.
The payment calculator is ordinary loan math. A $28,000 car, 6% tax, and $3,000 down is a $26,680 loan. At 6.9% for 60 months the payment is $527 and the interest is about $4,940. At 72 months the payment falls to $454 and the interest rises to about $5,980. You buy a $73 monthly break for about $1,040. The CFPB’s auto-loan guide is the checklist for the fees and add-on products this math never sees. Type the interest rate, not the APR.
The depreciation curve used on this site takes 20%, then 15%, then 13% off a new car. A $35,000 car is worth about $20,700 after three years. That is roughly $4,800 a year, which is often more than the fuel. The percents are a smooth rule of thumb, not a quote for your model. Look the car up before you believe them. Then put the annual loss into the true-cost calculator next to insurance, fuel, and maintenance. If depreciation is half the bar, a lower payment did not make the car cheap.
The gas calculator is miles divided by MPG times price. Twelve hundred miles a month at $3.49 is about $150 at 28 mpg and about $110 at 38 mpg, roughly $475 a year. Get the MPG from FuelEconomy.gov, not from the salesperson. An electric comparison belongs on the EV page: 12,000 miles at 28 mpg and $3.50 is $1,500 of gasoline, and the same miles at 30 kWh per 100 miles and $0.16 is $576. A $6,000 price gap takes about six and a half years of that fuel saving to close, before insurance and fast charging. The Department of Energy’s electricity basics explain why public charging is a different rate.
The tire size calculator reads the sidewall the way NHTSA describes it: width in millimeters, aspect ratio, radial, rim in inches. Overall diameter is the rim plus two sidewalls. A 225/65R17 is about 28.52 inches tall. A 235/55R18 is about 28.18 inches, 1.2% shorter. At an indicated 70 mph you are doing about 69. The 3% band the tool uses is a shop rule of thumb, not a federal limit. NHTSA’s instruction is to buy the size on the driver’s door placard or another size the vehicle maker lists. Match the load index before you celebrate a close percent. A taller tire makes the speedometer read low. A shorter one makes it read high.
If you are checking that the car in the ad is the car on the title, the VIN decoder calls NHTSA’s vPIC database. It will not tell you about salvage titles or accidents.
Last updated: October 29, 2026. Estimates only. Not tax, legal, financial, or professional advice. See the terms.