Air Conditioner Running Cost Calculator

How to use this calculator

1. Pick your country to preload a typical all-in electricity price, then replace it with the real price from your bill for an exact answer.
2. Enter the BTU rating of the unit (9,000, 12,000, 18,000 and 24,000 BTU are the common sizes).
3. Choose the efficiency rating printed on the label — SEER and EER are in BTU per watt-hour, COP is a plain ratio — and enter its value.
4. Set how long you run it, and the duty cycle.
5. Click Calculate running cost.

The formula, and the mistake most calculators make

Power drawn from the wall is the cooling capacity divided by the efficiency:

With COP instead of SEER, the BTU must first be converted to watts (1 W = 3.412 BTU/h):

Here is the mistake nearly every other calculator makes: it multiplies that nameplate power by the hours you run the unit. But an air conditioner does not draw full power the whole time. Once the room reaches the setpoint, an inverter unit throttles down to a fraction of its maximum, and a non-inverter unit switches off and on. Ignoring that overstates the bill by 30–40%.

This calculator asks for a duty cycle instead, and applies it. A correctly sized unit in a reasonably insulated room averages 60–75%. A badly undersized unit runs at nearly 100% and never quite gets there — which is why buying too small costs more, not less.

The cheapest way to cut the bill: one degree

Every degree you raise the setpoint cuts the compressor's work by roughly 8%. Going from 22 °C to 25 °C is not a small adjustment — it is around a quarter off the cooling bill, for a change most people stop noticing within a day. The calculator shows what a single degree is worth over your season.

Other levers, in rough order of value:

• Close the curtains on the sunny side. Solar gain through glass is often the single biggest load in the room.
• Clean the filters. A clogged filter can add 5–15% to consumption.
• Use the timer. Cooling an empty room is a pure loss.
• Do not set it colder to cool faster. It does not work that way — the unit cools at the same rate and simply overshoots past your target.

SEER, EER and COP — what the labels mean

EER is efficiency at one hot operating point. SEER is a seasonal average across a range of temperatures and part-load conditions, so it is always the higher number and the more realistic one for a whole summer. COP is the same idea expressed as a plain ratio of watts of cooling per watt of electricity — a SEER of 18 is roughly a COP of 5.3.

Practical range in 2026: a budget non-inverter unit sits around SEER 10–14; a good inverter split is SEER 18–22; the best are above 25. The gap between a SEER 12 and a SEER 20 unit is around 40% of the running cost, every summer, for the life of the machine — which is worth remembering when the cheaper unit is 200 currency units less.

Frequently asked questions

How much does it cost to run an air conditioner for one hour?

For a 12,000 BTU inverter unit at SEER 18, the draw is about 0.67 kW at full power and roughly 0.47 kW averaged over a realistic duty cycle. At 0.26 per kWh that is about 0.12 per hour. Enter your own figures above for an exact number.

How much does air conditioning add to my monthly bill?

A 12,000 BTU unit running 8 hours a day typically adds 100–120 kWh a month. Whether that is a small or a large amount depends entirely on your electricity price — which is exactly why the country preset matters.

Is an inverter air conditioner really cheaper to run?

Yes, materially. A non-inverter unit can only be fully on or fully off, so it overshoots and wastes energy on every cycle. An inverter modulates and holds the temperature at partial power. Expect 30–40% lower consumption for the same cooling.

Does setting a lower temperature cool the room faster?

No. The compressor works at the same rate regardless of the target you set; a lower setpoint only means it keeps working past the point you were comfortable. Set the temperature you actually want.

What duty cycle should I enter?

For a correctly sized unit in a reasonably insulated room, 60–75%. Use 80–90% for a poorly insulated room, a very hot climate or an undersized unit; 50% for a mild climate or a unit with generous capacity.

Is it cheaper to leave the air conditioner on all day?

Almost never. A room warms up slowly once you leave, and the unit spends the whole day fighting heat gain for nobody's benefit. Cooling a room back down when you return costs less than holding it cold all day.