Idaho vs Washington gas prices
Regular gas is $0.82 a gallon cheaper in Idaho — $12.24 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Idaho| Grade | ID | WA | Diff. | |
|---|---|---|---|---|
| Regular | $4.31 | $5.13 | $0.82ID | Idaho |
| Midgrade | $4.60 | $5.40 | $0.80ID | Idaho |
| Premium | $4.87 | $5.67 | $0.80ID | Idaho |
| Diesel | $5.32 | $6.18 | $0.86ID | Idaho |
Where the $0.82 gap actually comes from
25% of it is tax. Washington charges $0.20 more per gallon in federal and state taxes than Idaho. The remaining $0.62 is a real difference in what the fuel, refining and distribution cost — refinery proximity, pipeline access and state fuel-blend rules.
Fuel, refining, distribution and marginFederal and state taxes Pre-tax figures are estimates — see the note below.
What the gap is worth
Based on today’s $0.82 per-gallon difference, which moves week to week. Use the fuel cost calculator for your own mileage and vehicle.
Prices by metro area
State averages hide a lot. These are the cheapest metros AAA reports on each side.
Other comparisons
Frequently asked questions
Is gas cheaper in Idaho or Washington?
Regular gas is cheaper in Idaho, at $4.31 a gallon against $5.13 in Washington — a gap of $0.82, or 18.9%. On a 15-gallon fill-up that is $12.24. Figures are AAA daily state averages for 2026-08-02.
Why is gas more expensive in Washington?
25% of the $0.82 gap is tax rather than the cost of the fuel. Washington levies $0.20 more per gallon in federal and state taxes; the remaining $0.62 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Idaho or Washington?
Diesel is cheaper in Idaho at $5.32 a gallon, against $6.18 in Washington — $0.86 a gallon apart.
Is it worth crossing from Washington into Idaho to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $12.24. Driving out of your way for it rarely pays — at $5.13 a gallon and 25 mpg, a 30-mile round trip would eat the whole saving in fuel alone, before your time.