OTDMath turns each state's published rules into a step-by-step calculation. We do not use averages or guesses for tax rates, and every rule is linked to the official page it comes from.
The order of the calculation
- Taxable amount. We start from the vehicle price and apply the state's rules for trade-ins, rebates and dealer fees. For example, California does not subtract trade-ins, Texas does, and Florida taxes the dealer fee.
- Tax. We apply the state rate and any local rate that depends on where you register the car, including special limits such as Florida's surtax on the first $5,000.
- Government fees. We add the title, registration, plate and other fees the state or county charges when you title the car.
- Out-the-door price. Vehicle price − rebate + doc fee + taxes + fees. If you have a trade-in, we also show the amount due after it.
Where the data comes from
- State revenue departments and comptrollers (tax rates and rules).
- State DMVs and tax collectors (title and registration fees).
- State statutes and dealer regulators (doc fee caps).
Each state page lists its sources. Local rate tables come straight from the state: for example, California's district rates from the CDTFA table effective October 1, 2026.
What is an estimate
Some fees depend on details we don't ask for, such as the exact weight of the car or small county fees. Those lines are marked with ≈. Your county tax office or DMV sets the final amount.
How often we review
We review every state at least once a year in January, when most fee changes take effect, and whenever a state publishes new rates. The date of the last review is shown on every page. Last full review: October 19, 2026.
Found an error?
Tell us at our contact page with a link to the official source and we will fix it.