October 20, 2026
How much does it cost to run an air conditioner overnight?
Short answer
Running a 12,000 BTU air conditioner for an 8-hour night typically uses 4-7 kWh, because it cycles less once the room has cooled and outdoor temperatures fall after sunset. At the U.S. average rate of 17 cents per kWh that's roughly $0.70-1.20 a night, or $21-36 over a 30-night month. A larger unit, a hot climate or a time-of-use rate that charges more in the evening can push it higher. Using sleep mode and a setpoint of 76-80°F trims it further. Enter your own state and night-time hours below for a precise figure.
Running the AC while you sleep is the single most common reason people dread the summer bill. The good news: night is usually the cheapest time to cool, and a few settings make it cheaper still.
Why overnight costs less than daytime
Outdoor temperatures fall after sunset, so the AC has less heat to push out of the house. The same unit that cycles constantly at 3 p.m. may run only half the time at 2 a.m. The room is also not gaining heat from sunlight, cooking or people moving around.
What a night actually costs
Assume 8 hours of sleep and a 12,000 BTU unit that averages 500-900 watts over the night once the room has cooled down:
- Energy used: about 4-7 kWh per night.
- Cost at the U.S. average rate of 17 cents/kWh: roughly $0.70-1.20 a night, or about $21-36 for a 30-night month.
A larger unit, a hot climate or a poorly insulated bedroom pushes this up. A small, efficient unit in a mild-night climate can come in well below it.
Time-of-use rates change the math
If your utility charges more for electricity in the evening, the first few hours of the night can cost much more than the early morning. Some plans have a cheap overnight window. Check your rate schedule, then consider pre-cooling the bedroom during the cheap window and letting the temperature rise slowly before you wake.
Settings that lower the overnight bill
- Use sleep mode. Many units raise the setpoint by a degree or two over the first hours of the night, matching the body's natural cooling and trimming runtime.
- Aim for 76-80°F. Most people sleep comfortably a few degrees warmer than they sit during the day, especially with a fan on.
- Close the door and block the windows. Cooling one room is far cheaper than letting cold air leak into a hallway.
- Use a timer. Setting the AC to shut off or ease up in the early morning, when it is coolest outside, removes the hours you least need it.
Estimate your own night
Your cost depends on your unit's size, your state's rate and how many hours you really run it. Put those into the AC electricity cost calculator with your night-time hours to see a monthly figure for your bedroom, rather than a national average.