How much does it cost to run my AC?
Running cost is not a mystery number on your bill. It is three inputs multiplied together, and you already have all three.
"How much does it cost to run my air conditioner?" has a precise answer, and it does not require any stored price table — just your unit’s capacity, its efficiency and the electricity rate on your own bill. This guide walks through the method step by step so you can estimate cost per hour, per day and per cooling season.
The three inputs
Air-conditioner running cost is the product of three things: how much power the unit draws, how long it runs, and what you pay for electricity.
cost = power (kW) × hours × your $/kWh
The only slightly technical part is the power draw, and even that comes straight from the nameplate.
Step 1 — power draw from capacity and efficiency
Power is capacity divided by efficiency. Using EER (the single-point efficiency), kW = capacity (BTU/h) ÷ (EER × 1,000). A 36,000 BTU/h (3-ton) unit at EER 12 draws 36,000 ÷ (12 × 1,000) = 3.0 kW. If your spec sheet lists SEER2 rather than EER, convert first with EER ≈ SEER2 × 0.9 — see SEER vs SEER2 and the converter.
Step 2 — multiply by runtime
Estimate hours of actual compressor runtime, not just hours the system is switched on — on a mild day an AC may only run 40–60% of the time. For a worked example, take one hour of runtime: 3.0 kW × 1 h = 3.0 kWh.
Step 3 — multiply by your rate
At a rate of $0.15/kWh, 3.0 kWh costs $0.45 per hour of runtime. Run that unit 8 hours of compressor time a day and it is about $3.60/day; across a 120-day cooling season at that usage, roughly $430. The AC running-cost calculator runs this with your own numbers and never stores a price — the rate is always yours to enter from your utility bill.
Finding your real numbers
Two inputs trip people up. First, your electricity rate: look at the "price to compare" or total $/kWh on your bill, including delivery and supply charges, not just the supply rate — the all-in number is what actually leaves your wallet. If you are on a time-of-use plan, cooling often runs during the expensive afternoon peak, so use the peak rate for a realistic estimate. Second, runtime: the honest figure is compressor runtime, which you can estimate from how often you hear the unit cycle, or read from a smart thermostat’s usage report.
What raises and lowers the bill
Once you see the formula, the levers are obvious. A more efficient unit (higher EER/SEER2) cuts the kW term directly — the same 36,000 BTU/h at EER 14.4 draws 2.5 kW instead of 3.0, about 17% less. Right-sizing matters too: an oversized unit short-cycles and dehumidifies poorly, which can make you run it longer chasing comfort. Thermostat setbacks cut runtime hours — the setback-savings tool estimates that effect. And sealing ducts, shading windows and improving insulation all shrink the load the unit has to meet in the first place.
From an hour to a whole season
An hourly figure is easy; a seasonal one takes one more estimate — how many hours the compressor actually runs across the summer. The professional shortcut is equivalent full-load hours (EFLH): the number of hours the system would run if it ran at full capacity the whole time. EFLH varies by climate, from a few hundred hours in a cool northern city to well over a thousand in a hot southern one. Seasonal energy is then simply power (kW) × EFLH, and seasonal cost is that times your rate. Using the 3.0 kW unit from above at 800 EFLH: 3.0 × 800 = 2,400 kWh, and at $0.15/kWh, about $360 for the season.
If you would rather not estimate EFLH, a simpler path is to read your actual cooling-season kWh off your utility bills (the summer rise over your winter baseline is roughly the cooling load) and multiply by your rate. Either way, the point stands: no stored price table is involved — your bill and your unit’s nameplate contain everything the running-cost calculator needs.
Heat pumps in cooling mode
A heat pump running in cooling mode is just an air conditioner, so the same formula applies with its EER. In heating mode the math flips to COP and HSPF2, because the unit is moving heat in rather than out — use the heat-pump running-cost calculator, which uses kW = capacity ÷ (COP × 3,412). Either way, the principle is the same: capacity divided by efficiency gives power, power times hours gives energy, and energy times your rate gives dollars. No price database required — and because the formula rests on fixed physics, the estimate stays valid no matter what electricity prices do.