Car Payment Calculator
This car payment calculator goes beyond a plain auto loan estimate by rolling your sales tax and upfront dealer fees (title, registration, and documentation charges) directly into the financed amount, then subtracting your down payment and trade-in value. Sales tax is applied to the price net of the trade-in, matching how most US states assess vehicle tax. On top of the monthly payment it surfaces a total cost of ownership figure that combines every loan payment with the cash you put down, so you can see the full out-of-pocket picture rather than just the headline monthly number.
Formula
financed = price − down − tradeIn + taxes + fees; monthly = financed × r(1 + r)^n / ((1 + r)^n − 1)
- taxes
- Sales tax = (price − tradeIn) × tax% ÷ 100
- fees
- Upfront title, registration, and documentation fees rolled into the loan
- r
- Monthly rate = annual rate ÷ 12 ÷ 100
- n
- Number of payments = years × 12
How it works
- Enter the vehicle price, cash down payment, trade-in value, sales tax rate, and any upfront fees. The taxable base is the price minus the trade-in, and sales tax is calculated on that base.
- The financed amount is the price minus down payment and trade-in, plus the sales tax and fees. The annuity formula turns that balance, your rate, and your term into a monthly payment, and the calculator totals the interest and the overall cost of ownership.
Worked example
A $35,000 vehicle with $5,000 down, no trade-in, 6% sales tax, $800 in fees, financed at 6% over 5 years.
- Taxable base = 35,000 − 0 = $35,000; sales tax = 35,000 × 6% = $2,100.
- Financed amount = 35,000 − 5,000 − 0 + 2,100 + 800 = $32,900.
- Monthly = 32,900 × 0.005 × 1.005^60 ÷ (1.005^60 − 1) = $636.05; total payments = 636.05 × 60 = $38,163.
The monthly payment is about $636.05, the financed amount is $32,900 (including $2,100 tax and $800 fees), total interest is roughly $5,263, and total cost of ownership is about $43,163 once the $5,000 down payment is added.
Frequently asked questions
- What fees does this calculator include in the financed amount?
- It bundles the upfront dealer and government fees you typically roll into a car loan, such as title transfer, vehicle registration, and documentation (doc) fees. Enter their combined total in the fees field and they are added to the financed balance along with sales tax. It does not include recurring costs like insurance, fuel, or maintenance.
- How is sales tax handled when I have a trade-in?
- Sales tax is applied to the vehicle price after subtracting your trade-in value, which mirrors the rules in most US states that grant a trade-in tax credit. A larger trade-in therefore lowers both the taxable base and the tax you pay. If your state taxes the full price instead, enter the trade-in as zero to match that treatment.
- How does the down payment affect my monthly payment?
- The down payment is subtracted from the financed amount, so every dollar down lowers the balance you borrow and reduces both the monthly payment and the interest over the life of the loan. It still counts toward your total cost of ownership because it is cash you pay up front rather than money you avoid spending.