Washington’s state motor vehicle fuel tax is 49.4 cents per gallon, and the federal excise tax adds another 18.4 cents on gasoline, so the fixed tax on a gallon of regular gas in Washington comes to 67.8 cents before the fuel itself is priced. Diesel carries a heavier combined load of 73.8 cents per gallon, because the federal rate on diesel is 24.4 cents. Those are the numbers if you want a quick answer to how much the gas tax is in Washington state per gallon. The full picture is a little more involved, because a separate state carbon program adds a variable cost on top that can move the pump price by dozens of cents from one quarter to the next.
The State Rate
Under RCW 82.38.030, Washington charges 49.4 cents on every gallon of fuel used to power a vehicle on a public highway.1Washington State Legislature. RCW 82.38.030 – Tax Imposed Rate Incidence Allocation of Proceeds The rate applies to gasoline and diesel alike, and the statute defines “motor vehicle fuel” broadly enough to sweep in specialty blends and biodiesel mixes used on public roads.
Because the tax is a flat cents-per-gallon charge and not a percentage of the sale price, what you pay in state fuel tax stays the same whether crude is at $60 or $120 a barrel. That predictability makes budgeting easier for the state, but it also means the tax doesn’t move with inflation the way a percentage-based tax would.
The Federal Layer
The federal government adds its own per-gallon excise tax to every fuel sale nationwide: 18.4 cents on gasoline and 24.4 cents on diesel.2Federal Highway Administration. Federal Revenue Those rates have been frozen since 1993.
Federal revenue flows into the Highway Trust Fund. Roughly 15.44 cents of each gallon goes to the highway account, about 2.86 cents supports mass transit, and a tenth of a cent funds the Leaking Underground Storage Tank Trust Fund.3U.S. Energy Information Administration. Frequently Asked Questions – How Much Tax Do We Pay on a Gallon of Gasoline and on a Gallon of Diesel Fuel
Add the state and federal layers together and Washington gasoline carries 67.8 cents of fixed tax per gallon. Diesel carries 73.8 cents. Those totals help explain why filling up in Washington usually costs more than in Idaho or Oregon.
The Climate Commitment Act Adds a Variable Cost
Beyond the fuel tax itself, Washington runs a cap-and-invest program under the Climate Commitment Act (RCW 70A.65) that directly affects pump prices.4Washington State Legislature. Chapter 70A.65 RCW – Climate Commitment Act Large greenhouse gas emitters, fuel suppliers included, must buy carbon allowances at state-run auctions, and suppliers pass that cost through to drivers.
Voters had a chance to repeal the program in November 2024 through Initiative 2117 and rejected it by roughly 62% to 38%, so the program remains in effect. Unlike the fuel tax, the per-gallon cost of the program moves with each quarter’s auction results. Estimates have ranged from roughly 20 to 50 cents per gallon depending on market conditions.
The cap-and-invest charge is not legally a tax, and that distinction matters. The constitutional rule that forces fuel tax dollars into highway spending does not apply to cap-and-invest revenue, which funds climate programs, clean transportation, and environmental justice work instead of road maintenance.
Where the State Fuel Tax Money Goes
Every cent of the 49.4-cent state fuel tax is deposited into the Motor Vehicle Fund.5Washington State Legislature. RCW 46.68.090 – Distribution of Fuel Tax Revenue From there, a detailed formula sends money to state highways, counties, cities and towns, the Transportation Improvement Account, ferry operations, and bond retirement on earlier highway projects.6Washington State Department of Revenue. Motor Vehicle Fuel Tax Washington State Ferries, which functions as a floating extension of the highway network, receives a dedicated share through the Puget Sound Ferry Operations and Capital Construction accounts.
Article II, Section 40 of the Washington State Constitution locks fuel tax revenue into highway purposes exclusively. Lawmakers cannot redirect gas tax dollars to schools, social services, or the general fund.7Office of the Attorney General. Applicability of Article II Section 40 of the Washington Constitution to Proposed Excise Tax That protection, adopted in 1944 as Amendment 18, is why the money you pay at the pump has a direct line to the road system.
Refunds for Fuel Used Off the Road
If you burn fuel off the public road system, you shouldn’t be paying highway taxes on it. Under RCW 82.38.180, anyone who paid at least $20 in Washington fuel tax during the past 13 months can apply for a refund on fuel used for non-highway purposes.8Washington State Legislature. RCW 82.38.180 – Refunds Qualifying uses include:
- Farming and logging equipment that never touches a public road, such as tractors and harvesters
- Construction equipment like generators, compressors, and earthmovers on job sites
- Recreational and commercial marine fuel
- Commercial mowing and grounds maintenance equipment
- Power take-off equipment, such as the hydraulic dump mechanism on a dump truck or the boom on a crane truck
To claim a refund, you first need a fuel tax refund account through the Washington Department of Licensing. Claims can be filed monthly, quarterly, or for a six-month period, and must be submitted within 13 months of the fuel purchase date. Fuel invoices have to be included, and the department won’t accept altered or highlighted receipts.9Washington State Department of Licensing. Fuel Tax Refunds At 49.4 cents per gallon, the refund is worth the paperwork for anyone running heavy equipment off-road.
Federal off-highway fuel use qualifies for a credit too, claimed on IRS Form 4136.10Internal Revenue Service. About Form 4136 Credit for Federal Tax Paid on Fuels Combined with the state refund, someone using gasoline entirely off-road can recover close to 68 cents on every gallon.
What Electric and Hybrid Drivers Pay Instead
Drivers who skip the pump still owe the state for road use. Washington charges electric vehicles and qualifying plug-in hybrids a $75 annual transportation electrification fee at registration renewal. The fee applies to any vehicle with at least one propulsion method rechargeable from an external electricity source that can travel at least 30 miles on battery power alone.11Washington State Legislature. Washington Code 46-17-324 – Transportation Electrification Fee Hybrid and alternative fuel vehicles below the 30-mile battery threshold pay a separate $75 hybrid vehicle fee instead.
For a fully electric vehicle, the total annual fee comes to $150 once the transportation electrification fee is combined with the standard EV registration surcharge under RCW 46.17.323. A driver covering 12,000 miles a year in a 30-mpg gas car pays roughly $198 in state fuel tax alone, so the EV fee does not fully close the gap.