Calculation Methodology & Sources
Every formula, rounding protocol, and statutory data source used across CarTaxCalc engines explained in technical detail.
1. The Out-the-Door Price Core Algorithm
All calculations across our Out-the-Door Price Calculator and state engines execute deterministic floating-point arithmetic verified down to the cent ($0.01).
Statutory Computation Steps
- Net Taxable Base Assessment:
Taxable Basis = Credit Applies ? max(0, Price - TradeIn) : Price
In states permitting trade-in tax credits (42 states), the trade-in allowance directly reduces the taxable base. In non-credit jurisdictions (California, Virginia, DC), taxable basis equals gross price. - Sales Tax Computation:
Sales Tax = round(Taxable Basis × (Tax Rate / 100), 2)
Taxes are rounded to two decimal places using standard half-up arithmetic. - Out-the-Door Total Cash Due:
OTD Total = max(0, (Price - TradeIn - Rebates) + Sales Tax + Doc Fee + DMV Title/Reg + Other Fees)
2. Primary Statutory Data Sources
CarTaxCalc references primary legislative statutes and state Department of Revenue circulars:
- Texas: Texas Tax Code § 152.021 (6.25% motor vehicle sales and use tax) and § 152.041 (trade-in deduction).
- California: Cal. Rev. & Tax. Code § 6012 (gross receipts tax) and Cal. Veh. Code § 11713.1 ($85 doc fee cap).
- Florida: Fla. Stat. § 212.054 (county discretionary surtax cap on first $5,000) and Florida Department of Revenue Form DR-15DSS.
- Ohio: Ohio Rev. Code § 4517.261 ($398 doc fee cap for 2026) and § 5739.01(H)(2) (new vehicle trade-in exemption).
- Pennsylvania: 72 P.S. § 7202 (sales and use tax) and PennDOT Bulletin 2024-01 ($490 electronic titling cap / $409 manual).
- North Carolina: N.C. Gen. Stat. § 105-187.3 (3.0% Highway Use Tax).
- Illinois: 35 ILCS 120/ (Retailers' Occupation Tax) and 815 ILCS 375/11.1 ($377.63 doc fee cap).
- Georgia: O.C.G.A. § 48-5C-1 (7.0% Title Ad Valorem Tax).
- Virginia: Va. Code § 58.1-2402 (4.15% Motor Vehicle Sales and Use Tax).
- Arizona: A.R.S. § 42-5061 (Transaction Privilege Tax).
- Washington: RCW 82.08.020 (state vehicle tax) and RCW 46.70.180 ($200 doc fee cap).
- Missouri: Mo. Rev. Stat. § 144.020 (state motor vehicle sales tax) and § 301.558 ($565.04 doc fee cap).
3. Quarterly Legislative Review Schedule
State legislatures frequently index doc fee caps to the Consumer Price Index (CPI) on January 1st and adjust local tax boundaries on July 1st. CarTaxCalc executes quarterly statutory reviews to verify all state rules against state revenue bulletins.