State Gas Tax Calculator
Every gallon of gasoline carries a federal excise tax of 18.4 cents plus a state motor-fuel tax that varies by state. This calculator combines the federal rate (pre-filled, editable) with the state cents-per-gallon rate you enter to show the tax on a single fill-up, the combined rate per gallon, and the total fuel tax you pay over a year based on your typical annual gallons. Look up your current state rate on your state revenue or transportation department before relying on the figures.
Gas tax formula
Combined rate ($/gal) = (federal cents + state cents) / 100
Tax per fill-up = combined rate * gallons per fill-up
Annual fuel tax = combined rate * gallons per year
Annual federal portion = (federal cents / 100) * gallons per year
Cents-per-gallon rates are divided by 100 to convert to dollars. The federal rate is fixed by statute; state rates are set by each state and entered by you.
U.S. gas tax context
- The federal gasoline excise tax is 18.4 cents per gallon (18.3 cents Highway Trust Fund plus 0.1 cent LUST fund).
- Federal diesel tax is 24.4 cents per gallon, higher than gasoline.
- State per-gallon rates vary widely and some are indexed to inflation or wholesale price.
- Some states add a percentage sales tax on top of the per-gallon excise tax.
- Federal fuel-tax revenue mainly funds the Highway Trust Fund for highways and transit.
State gas tax: frequently asked questions
How much is the federal gas tax?
The federal excise tax on gasoline is 18.4 cents per gallon, set in the Internal Revenue Code (26 U.S.C. 4081). Of that, 18.3 cents funds the Highway Trust Fund and 0.1 cent funds the Leaking Underground Storage Tank trust fund. Diesel is taxed at a higher 24.4 cents per gallon. This calculator pre-fills the gasoline rate but lets you edit it.
Why do I enter the state gas tax myself?
State motor-fuel tax rates differ widely and many states adjust them periodically (some index to inflation or wholesale price). To stay accurate, this calculator takes the state cents-per-gallon rate as an editable input. Look up your state's current rate on your state department of revenue or transportation website.
Are sales taxes on gasoline included?
Some states apply general or special sales tax to fuel in addition to the per-gallon excise tax. This calculator handles the per-gallon excise components. If your state also charges a percentage sales tax on fuel, add that separately, because it depends on the pump price rather than gallons.
How is the tax per fill-up calculated?
Multiply the combined federal plus state cents-per-gallon rate by the number of gallons you buy. For a 12-gallon fill-up at a combined rate of 50 cents per gallon, the excise tax is $6.00. The annual figure multiplies your typical annual gallons by the same combined rate.
Where does gas tax revenue go?
Federal gas tax revenue primarily funds the Highway Trust Fund, which pays for highway and mass transit projects. State fuel taxes generally fund state road construction and maintenance. The specific allocation varies by state law and the federal Highway Trust Fund statute.
Official sources
- U.S. Internal Revenue Service: Excise Tax.
- U.S. Energy Information Administration: Gasoline and Diesel Fuel Update.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.