How much does an air conditioner cost per month?

Each row runs 8 hours of compressor time a day for 30 days, the default in the site's cooling calculators. Watts come from the rating: cooling BTU per hour divided by SEER2 (central and mini split) or CEER (window and portable units).

Air conditioner	Running watts	kWh a month	US average	Texas	Arizona
Central, 3 tons, SEER2 14	2,571	617	$112.05	$98.16	$92.86
Central, 3 tons, SEER2 18	2,000	480	$87.17	$76.37	$72.24
Two window units, 8,000 BTU, CEER 11	1,455	349	$63.38	$55.53	$52.52
Window unit, 12,000 BTU, CEER 11	1,091	262	$47.58	$41.68	$39.43
Portable, 8,000 BTU, CEER 7	1,143	274	$49.76	$43.59	$41.24
Window unit, 8,000 BTU, CEER 11	727	175	$31.78	$27.84	$26.34
Mini split, 12,000 BTU, SEER2 20	360 average	86	$15.62	$13.68	$12.94

The mini split row uses the calculator's modulation factor of 0.6: an inverter unit rarely runs at full power, so its average draw is about 60% of its maximum (600 W for a 12,000 BTU unit at SEER2 20). A portable unit costs more than a window unit of the same size because its rating (CEER, using the SACC test) is lower: a single-hose portable loses about 30% of its nominal capacity under that test.

Eight hours a day is a mild-summer figure. In a hot July the compressor can run most of the day, which is where the climate section below comes in.

Watts are the easy part. Hours vary far more: the same air conditioner runs several times as many hours a year in Florida as in Minnesota. The site's SEER2 savings calculator uses full-load cooling hours by climate zone: the hours a system would run at 100% to deliver a year's cooling. Here is what that means for a 3-ton, SEER2 14 central system, with the peak month at about 26% of the year's cooling (July, in a typical US pattern):

Zone	Example state	Cooling degree-days	Full-load hours a year	kWh a year	Peak month kWh	Peak month cost
1	Hawaii	4,400	2,400	6,171	1,605	$757.24
2	Florida	3,300	2,000	5,143	1,337	$200.42
2	Arizona	3,800	2,000	5,143	1,337	$201.22
3	Georgia	1,800	1,500	3,857	1,003	$159.48
4	US average	1,300	1,100	2,829	736	$133.66
5	New York	800	800	2,057	535	$153.28
6	Minnesota	600	600	1,543	401	$68.97
7	North Dakota	500	400	1,029	267	$35.54

Cooling degree-days (NOAA 1991–2020 normals) measure how hot a summer is; the zone is the IECC climate zone. Our hours go by zone, so two states in the same zone, like Arizona and Florida, get the same hours even though Arizona's summer is hotter by degree-days. If your house is in a hot spot within a zone, or the AC is undersized and runs all afternoon, expect more.

The cooling season is concentrated. In our model, July and August together carry half of the year's cooling, and May through September about 90% of it. Divide the yearly kWh by 12 and you'll underestimate your summer bills by more than half.

A family in Texas (zone 2, electricity 15.9¢/kWh) with a 3-ton central system at SEER2 14 is looking at the July bill. In our model, July is about 1,337 kWh of cooling, about 520 full-load hours or close to 17 hours a day. That's $212.72 for the month, more than the average Texas bill of $175.00, which averages all twelve months and every use.

Three ways to cut it:

• Replace with SEER2 18. The same cooling takes 14 ÷ 18 = 78% of the electricity: about 1,040 kWh in July, $165.46, saving $47.25 that month.
• Cool fewer rooms. If the family only needs the bedrooms and living room at night, two 8,000 BTU window units running 8 hours use 349 kWh a month, $55.53. They won't hold a whole house at 75 °F through a Texas afternoon, though.
• Mini splits for the main rooms. Two 12,000 BTU heads at SEER2 20 and 60% modulation, running 12 hours a day, use about 259 kWh a month, $41.21.

Compare your own setup in the window vs central air calculator.

SEER2 is the cooling delivered over a season divided by the electricity used. Since a unit's power draw is its capacity divided by SEER2, the saving from a higher rating is a fixed percentage of your cooling kWh:

Upgrade from SEER2 14 to	Uses this much less electricity
16	12.5%
17	17.6%
18	22.2%
20	30.0%

What that percentage is worth depends on how much you cool. Going from SEER2 14 to 17 on a 3-ton system saves about 908 kWh a year in Florida ($136.11), 681 kWh in Georgia ($108.28), 499 kWh at the US average ($90.62), 363 kWh in New York ($104.00) and 272 kWh in Minnesota ($46.78). Divide the price difference between two quotes by the yearly saving to get the payback. The same upgrade is worth several times more in a hot state with high rates than in a cool state with low ones.

SEER2 replaced SEER in 2023. Its test uses higher fan pressure, so a unit's SEER2 is about 0.95 × its old SEER rating. When you compare quotes, compare SEER2 with SEER2.

• Central air cools the whole house through ducts and is the only option that does so evenly. It also has the highest draw. Leaky ducts in a hot attic waste part of what it makes.
• Window units are the cheapest to buy and to run per room, but each one cools a room or two. Several running at once can match a small central system's draw.
• Mini splits have the highest ratings and modulate down instead of cycling on and off, so they cost the least per BTU of cooling. They cost more to install per room than a window unit.
• Portable units are the most expensive way to cool a room. Use one only where a window unit can't go.

Size matters too. An oversized unit cools the room before it has removed the humidity, and an undersized one runs all day without catching up. The BTU calculator gives the size for a room.

• Central AC cost calculator: your tons, SEER2 and hours, at your state's rate.
• Window AC cost calculator and mini split cost calculator: per unit, with the mini split's heat mode too.
• SEER2 savings calculator: yearly saving and payback for an upgrade in your climate zone.
• Ceiling fan vs AC calculator: what a fan costs next to the air conditioner it lets you turn down.

If summer is when your bill jumps, the why is my electric bill so high guide walks through the other usual causes.