Air Conditioner Running Cost Calculator

How air conditioner cost is calculated

Air conditioners are rated in BTU per hour, the amount of heat they can remove. What you pay for is the electricity needed to move that heat, and the ratio between the two is the efficiency rating on the label. For a window or portable unit that is the EER; for central and mini-split systems it is SEER, a seasonal average.

Watts ≈ BTU per hour ÷ EER. A 12,000 BTU window unit with an EER of 11 draws about 1,090 W. A 36,000 BTU (3-ton) central system with a SEER of 14 draws in the region of 3,000 to 3,500 W including the indoor blower. Once you have watts, the rest is the usual math: watts × running hours ÷ 1,000 = kWh, then kWh × your rate.

The one number people get wrong is running hours. Unless the unit is undersized or it is brutally hot, a thermostat-controlled AC does not run continuously. It cools the space to the setpoint, shuts the compressor off, and restarts when the temperature drifts up. The calculator wants the hours the compressor actually runs. If you do not know, use half the hours the unit is switched on for warm weather and three-quarters for a heat wave.

Typical costs by AC type

All figures use the U.S. average residential rate of 18.34¢ per kWh (June 2026, EIA) and a 30.4-day month. Pick your state in the calculator to adjust.

Two things stand out. The mini-split is far cheaper per BTU than a window unit of the same size because inverter compressors slow down instead of switching off, which is why they have become the default in new installations. And central AC dominates the summer bill for the simple reason that it cools every room, including the ones nobody is in.

What actually drives your AC bill

• The temperature difference. Every degree you lower the thermostat below the outdoor temperature costs more than the last, because heat leaks into the house faster. The Department of Energy's rule of thumb is about 3% less cooling energy for each degree you raise the setpoint. 78°F when home and 85°F when out is the common recommendation.
• Insulation and air sealing. Attic insulation and sealed ducts can cut run time by a quarter or more. Leaky ducts in a hot attic are one of the most common reasons a central system runs far longer than it should.
• Filters and coils. A clogged filter forces the blower to work harder and reduces heat transfer at the coil, so the compressor runs longer for the same cooling. Change the filter every one to three months in summer.
• Sun through windows. A south or west facing window can add 1,000 BTU per hour or more on a sunny afternoon. Closing blinds during the day is the cheapest efficiency upgrade there is.
• Humidity. Removing moisture takes energy. In humid climates, a dehumidifier or a properly sized AC (not oversized) makes 78°F feel like 75°F.

Practical ways to spend less

1. Set it and leave it. Constantly changing the setpoint makes the system cycle inefficiently. A programmable or smart thermostat with a daily schedule pays for itself in one summer.
2. Use ceiling fans with it. A 60 W fan lets you raise the setpoint 4°F without feeling warmer. Turn fans off in empty rooms; they cool people, not air.
3. Cool one room at night. A 5,000 BTU window unit in the bedroom costs about 66¢ per 8-hour night. Central AC across the whole house for the same night is around $3.21 even at a modest 5 hours of run time.
4. Shift use on time-of-use plans. Pre-cool the house to 74°F before the 4 to 9 pm peak window, then let it drift to 78°F through the peak. See our time-of-use guide.
5. Mind the age. A 20-year-old 10 SEER central unit uses about 40% more electricity than a new 16 SEER unit for the same cooling. If the old unit runs 1,000 hours a summer, that difference is worth about $257 a season.

Winter's equivalent of this page is the space heater cost calculator. For the full picture of which appliances dominate a bill, read the most expensive appliances to run.