What is Montana's gas tax rate?

Montana levies a state gasoline excise of about 33.0 cents per gallon and a diesel excise near 29.75 cents per gallon. On top of that, the federal excise adds 18.4 cents per gallon on gasoline and 24.4 cents on diesel, so the combined tax is roughly 51 cents per gallon of gasoline.

Is gas tax added at the pump like sales tax?

No. Fuel excise taxes are built into the per-gallon price you see on the pump, not added at checkout the way a percentage sales tax is. Montana also has no general sales tax, so the only tax on a gallon of gas is the per-gallon excise.

How much gas tax do I pay per year?

It depends on how much you drive and your fuel economy. Divide your annual miles by your MPG to get gallons used, then multiply by the combined per-gallon rate. A driver covering 12,000 miles at 25 MPG burns about 480 gallons and pays roughly $246 in combined gas tax per year.

Does Montana index its gas tax to inflation?

Montana raised its fuel tax in steps under a 2017 law rather than indexing it automatically to inflation, so the rate changes only when the legislature acts. Always confirm the current cents-per-gallon figure with the Montana Department of Transportation before budgeting precisely.

Why is the tax per mile useful?

Tax per mile lets you compare the road-tax cost of different vehicles and is the basis for proposed mileage-based road-usage fees. A thirstier vehicle pays more fuel tax per mile, while an efficient one pays less, which is why states are studying per-mile charges as fuel economy rises.

Montana Gas Tax Calculator

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Montana funds its highways largely through a per-gallon fuel excise rather than a percentage sales tax — in fact the state has no general sales tax at all. The gasoline excise is about 33.0 cents per gallon, with diesel near 29.75 cents, and the federal excise stacks on top. This tool turns those rates into tax per fill-up, per year, and per mile.

How it works

The tool multiplies gallons by the combined per-gallon rate:

combined rate = state excise + federal excise (per gallon)
per fill-up   = tank size × combined rate
gallons/year  = annual miles ÷ MPG
annual tax    = gallons/year × combined rate
tax per mile  = annual tax ÷ annual miles

For gasoline the combined rate is roughly 0.330 + 0.184 = $0.514 per gallon. Because the excise is embedded in the pump price, you do not see it as a separate line at checkout.

Example and notes

Filling a 14-gallon tank with gasoline carries about 14 × 0.514 = $7.20 in combined fuel tax. Driving 12,000 miles a year at 25 MPG burns ~480 gallons and pays roughly $247 in fuel tax annually, or about $0.021 per mile. Diesel uses slightly different rates. Confirm the current Montana rate with the Montana Department of Transportation, since it changes only by legislative action.