Idaho vs Montana gas prices
Regular gas is $0.03 a gallon cheaper in Montana — $0.41 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Idaho
Montana| Grade | ID | MT | Diff. | |
|---|---|---|---|---|
| Regular | $4.31 | $4.28 | $0.03MT | Montana |
| Midgrade | $4.60 | $4.61 | $0.02ID | Idaho |
| Premium | $4.87 | $4.97 | $0.10ID | Idaho |
| Diesel | $5.32 | $5.09 | $0.23MT | Montana |
Where the $0.03 gap actually comes from
0% of it is tax. Idaho charges $0.00 more per gallon in federal and state taxes than Montana. The remaining $0.03 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 $0.03 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 Montana?
Regular gas is cheaper in Montana, at $4.28 a gallon against $4.31 in Idaho — a gap of $0.03, or 0.6%. On a 15-gallon fill-up that is $0.41. Figures are AAA daily state averages for 2026-08-02.
Why is gas more expensive in Idaho?
0% of the $0.03 gap is tax rather than the cost of the fuel. Idaho levies $0.00 more per gallon in federal and state taxes; the remaining $0.03 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Idaho or Montana?
Diesel is cheaper in Montana at $5.09 a gallon, against $5.32 in Idaho — $0.23 a gallon apart.
Is it worth crossing from Idaho into Montana to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $0.41. Driving out of your way for it rarely pays — at $4.31 a gallon and 25 mpg, a 1-mile round trip would eat the whole saving in fuel alone, before your time.