How much does a window air conditioner cost per month in Montana?

About $8.97 a month, assuming 900 W at a 80% duty cycle, 8 hours a day, 120 days a year at 15.57¢/kWh.

How many kilowatt-hours does a window air conditioner use?

Roughly 691 kWh a year under these assumptions, or 0.72 kWh for every hour it runs.

Is that expensive compared with other states?

Montana has the 19th cheapest average residential rate in the country, so this appliance costs less here than the U.S. average of $126 a year.

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Cost to run a window air conditioner in Montana (August 2026 rates)

At 15.57¢ per kilowatt-hour — Montana's average residential price in August 2026 — running a window air conditioner costs $108 a year. That is 14% less than the national average of $126. Montana's residential rate is up 9.0% from August 2025, which moves this appliance from $98.77 to $108 a year.

Per hour: 11.2¢
Per day of use: 89.7¢
Per month: $8.97
Per year: $108

Assumption: 900 W at a 80% duty cycle, 8 hours a day, 120 days a year — 691 kWh a year. Typical of a 10,000 BTU window unit. Small 5,000 BTU units draw closer to 500 W; 15,000 BTU units closer to 1,400 W. Use the calculator to swap in the numbers from your own model.

How Montana compares

Montana pays 15.57¢/kWh, the 19th cheapest residential electricity of the 51 U.S. jurisdictions EIA reports. For this appliance that works out to $17.90 less a year than the typical U.S. household pays for the same use. Running the same window air conditioner costs $87.92 a year in Nevada and $326 in Hawaii, so where you live changes this bill by $238 a year.

State	Rate	Per month	Per year
South Dakota	15.15¢	$8.73	$105
Kansas	15.47¢	$8.91	$107
Montana	15.57¢	$8.97	$108
South Carolina	15.76¢	$9.08	$109
Georgia	15.90¢	$9.16	$110

States ranked by average residential price, cheapest first. See all 51 states for a window air conditioner.

What else costs about the same in Montana

Electric clothes dryer$121 a year in MT Aquarium$92.07 a year in MT Gaming pc$90.93 a year in MT

Cutting the number down

Sealing the gaps around the sleeve with foam matters more than the unit's efficiency rating. Warm air leaking back in is load you pay to remove twice.
An inverter model modulates instead of slamming on and off, which shows up as a lower effective duty cycle rather than a lower nameplate watt.
Shading the outdoor half of the unit lowers the temperature it rejects heat into, which lowers the work it has to do.

Questions

How much does a window air conditioner cost per month in Montana?: About $8.97 a month, assuming 900 W at a 80% duty cycle, 8 hours a day, 120 days a year at 15.57¢/kWh.
How many kilowatt-hours does a window air conditioner use?: Roughly 691 kWh a year under these assumptions, or 0.72 kWh for every hour it runs.
Is that expensive compared with other states?: Montana has the 19th cheapest average residential rate in the country, so this appliance costs less here than the U.S. average of $126 a year.