How much does it cost to run an air conditioner per month?

It depends on the unit’s size, efficiency, and how hard it runs, but at $0.17/kWh and 8 hours a day, a 12,000 BTU window unit costs about $31 a month and a 3-ton central system about $80. A small window unit can be as low as $16, while a 5-ton central system in a hot climate can top $145. Your real figure moves with your electricity rate and the compressor’s duty cycle, so enter both for your own situation rather than relying on an average.

Does a higher SEER air conditioner actually save money?

Yes, but with diminishing returns. Running cost scales inversely with efficiency, so moving from SEER 14 to SEER 20 cuts the per-BTU cost by roughly a third, which is real money on a central system you run all summer. The catch is that high-SEER units cost more up front, and the savings only pay back if you run the AC enough hours. A unit used a few weeks a year rarely justifies the premium over a mid-SEER model.

Why does my air conditioner cost more to run than the calculator estimate?

The most common reason is duty cycle. If the estimate assumes 70% but your unit runs near 100% because it is undersized, the room is poorly insulated, or the weather is extreme, real cost climbs in proportion. The other big factor is your electricity rate: summer tiers and time-of-use peaks can push the effective rate well above the annual average. Check a recent bill rather than using a round number.

Is it cheaper to run one central AC or several window units?

It depends on how much of the house you cool. Cooling one or two rooms with window units is usually cheaper than running a whole central system, because you move far less total heat. But if you need the entire house cool, a single right-sized central system or a multi-zone mini-split is typically more efficient per BTU than a houseful of window units, especially at higher SEER ratings. Match the approach to how many rooms you actually use.

How do I find my air conditioner’s wattage if the label only shows BTU?

Divide the BTU rating by the efficiency rating. For a window unit labelled EER, watts equal BTU per hour divided by EER, so a 10,000 BTU unit at EER 10 draws about 1,000 watts at full load. For a central unit labelled SEER, convert SEER to an approximate EER first, then divide; this calculator does that step for you. The figure you get is full-load draw, so multiply by the duty cycle for the realistic average.

AC Running Cost Calculator — BTU, SEER & Hours

7 min read

The air conditioner running cost calculator turns the two numbers on your AC’s label, its cooling capacity in BTU and its EER or SEER efficiency rating, into a real dollar figure per day, month, and year. Cooling is the single largest summer load in most homes, so small differences in efficiency and run time add up fast. Two things drive the result more than anything else, and both are yours to set: the electricity rate you actually pay, and how hard the compressor works (its duty cycle). Enter your own rate rather than trusting a national average, and treat every figure here as an estimate, because actual cost shifts with your climate, insulation, and how often the compressor cycles. For appliances you can read a wattage off directly, the appliance electricity cost calculator skips the BTU step.

Air conditioner running cost banner comparing a window unit at 31 dollars a month with a central system at 80 dollars.

How the BTU-to-Dollars Math Works

Every cost estimate starts by turning cooling capacity into electrical draw. The EER on a unit’s label is its cooling output in BTU per hour divided by its power input in watts, so the full-load draw is simply BTU/hr ÷ EER. A 12,000 BTU unit rated EER 11 pulls about 1,091 watts when the compressor is running flat out.

Central systems and mini-splits are not labelled in EER. They carry a SEER (or SEER2) rating, a seasonal average measured across a range of outdoor temperatures rather than a single full-load point. This tool converts SEER to an equivalent EER using a widely-used DOE-standard approximation before working out watts. That conversion is genuinely approximate, so a SEER-rated estimate carries more uncertainty than an EER-rated one; real instantaneous efficiency varies by equipment.

Watts alone do not set the bill. A compressor rarely runs continuously; it cycles on and off to hold the thermostat setpoint. The fraction of time it actually runs is the duty cycle, and it is the largest single source of real-world variation. Multiply the average draw by the hours the unit is on, divide by 1,000 for kilowatt-hours, then multiply by your rate. For the raw watts-to-kWh step on any load, the kWh calculator shows the same arithmetic.

Bar chart of monthly air conditioner running cost by unit, from a small window unit to a five-ton central system. — Estimates assume 8 hrs/day, a 70% duty cycle, and $0.17/kWh — real cost shifts with your rate, duty cycle, insulation, and climate.

What Common AC Units Cost Per Month

The table below runs seven representative units through the same assumptions: 8 hours a day, a 70% duty cycle, and $0.17/kWh. Avg draw is the compressor’s average power after duty cycle; monthly cost is 30 days at that draw.

Unit	Capacity	Rating	Avg Draw	Monthly Cost*
Small window	6,000 BTU	EER 11	382 W	$15.58
Mini-split	12,000 BTU	SEER 20	583 W	$23.80
Medium window	12,000 BTU	EER 11	764 W	$31.16
Portable	12,000 BTU	EER 9	933 W	$38.08
Central 2-ton	24,000 BTU	SEER 15	1,366 W	$55.73
Central 3-ton	36,000 BTU	SEER 16	1,969 W	$80.33
Central 5-ton	60,000 BTU	SEER 14	3,571 W	$145.71

*At $0.17/kWh, 8 hrs/day, 70% duty cycle. Two patterns stand out. A high-efficiency mini-split costs far less to run than a window unit of the same BTU ($23.80 versus $31.16 a month here) because its seasonal rating is so much higher. And central systems dominate the bill purely on size: a 5-ton unit moves five times the heat of a 1-ton window unit, so it costs roughly nine times as much to run.

Cutting Your AC Running Cost

Raise the setpoint a few degrees. Each degree higher cuts run time and the compressor cycles less, dropping duty cycle. Going from 70°F to 76°F trims cooling cost 15-25% in a typical home.
Right-size the unit. An oversized AC short-cycles and an undersized one runs near 100% duty in heat, and both cost more than a correctly matched unit. Match BTU to the room, not to the biggest box on the shelf.
Replace a low-SEER central system. Swapping a SEER 14 unit for a SEER 20 mini-split cuts the per-BTU running cost by about a third. Use the electricity bill estimator to see the whole-home impact across every category.
Offset cooling with solar. AC load peaks in the afternoon, exactly when rooftop panels produce most. The solar ROI calculator shows the payback period when summer cooling is the load you are sizing for.

Worked Examples

A Window Unit Through a Hot Month

Context

You run a 12,000 BTU window air conditioner rated EER 11 for 8 hours a day during a hot stretch. In your area the compressor runs about 70% of that time, and your electricity rate is $0.17/kWh. What does the unit cost for the month?

Calculation

Full-load draw: 12,000 BTU/hr ÷ 11 EER = 1,091 W

Average draw at 70% duty: 1,091 × 0.70 = 764 W

Daily energy: 764 W × 8 h ÷ 1,000 = 6.11 kWh

Monthly cost: 6.11 kWh × 30 × $0.17 = $31.16

Interpretation

About $31 a month while you are running it hard. Because EER maps straight to watts, this is the most direct of the two rating paths, with no SEER conversion involved. Cost scales directly with duty cycle, so the same unit costs noticeably less in mild weather when the compressor cycles off more often.

Takeaway

For a quick estimate on any single device where you already know the wattage, the electricity cost calculator takes watts directly and skips the BTU and efficiency step.

A 3-Ton Central System on SEER

Context

Your home has a 3-ton central air conditioner, which is 36,000 BTU/hr, rated SEER 16. It runs 8 hours a day at a 70% duty cycle, and you pay $0.17/kWh. What is the monthly running cost?

Calculation

SEER to EER: −0.02 × 16² + 1.12 × 16 = 12.80 EER

Full-load draw: 36,000 BTU/hr ÷ 12.80 = 2,813 W

Average draw at 70% duty: 2,813 × 0.70 = 1,969 W

Daily energy: 1,969 W × 8 h ÷ 1,000 = 15.75 kWh

Monthly cost: 15.75 kWh × 30 × $0.17 = $80.33

Interpretation

About $80 a month for the season’s peak usage. The SEER 16 rating converts to 12.80 EER, noticeably lower than the headline SEER — that gap is the seasonal-average effect, and it is why a SEER number alone overstates how cheaply a unit runs at full load on the hottest days.

Takeaway

Running central AC during an outage means a large inverter and battery bank. The solar panel and battery sizing calculator sizes the system around a load this size.

Frequently Asked Questions

Glossary

BTU and Tons

A British Thermal Unit (BTU) is the heat needed to raise one pound of water by one degree Fahrenheit; for air conditioners, capacity is quoted in BTU per hour. A ton of cooling equals 12,000 BTU/hr, so a 3-ton unit is 36,000 BTU/hr. Window units typically run 5,000 to 14,000 BTU/hr; central systems run 24,000 to 60,000.

EER (Energy Efficiency Ratio)

EER is a unit’s cooling output in BTU per hour divided by its electrical input in watts, measured at a single full-load test point (95°F outdoor). It maps directly to power draw: watts equal BTU/hr divided by EER. Window, portable, and PTAC units are labelled in EER or the closely related CEER.

SEER and SEER2

SEER is the seasonal version of EER: total cooling output across a simulated cooling season divided by total watt-hours consumed, so it averages in part-load and milder temperatures. SEER is always higher than the same unit’s EER. Central systems and mini-splits are rated in SEER, or SEER2 under the test procedure adopted in 2023.

Duty Cycle

The duty cycle is the share of time the compressor actually runs while the unit is switched on. A correctly sized AC in mild weather might run 50 to 60% of the time; in a heatwave or when undersized it can run near 100%. Because energy use scales with run time, duty cycle is the largest source of real-world cost variation.

AC is usually the top line on a summer bill, but the same method ranks every load — our guide to what household appliances really cost to run walks through the 30-minute audit.

The honest takeaway: an air conditioner’s running cost is set less by the sticker efficiency than by how you run it. Duty cycle, your local rate, insulation, and outdoor temperature each move the number more than a point or two of SEER does. The duty-cycle table built into the results panel makes that explicit — the same unit can cost half as much in mild weather as it does in a heatwave. Use the calculator to compare units before you buy and to sanity-check a bill that looks high, but pair it with your real rate from a recent statement. For how that rate is actually built from energy, delivery, and demand charges, our guide to electricity costs breaks down the line items.

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Last updated: June 30, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. He works professionally as Commercial Director at Ezoic Inc., leading revenue strategy across digital publishing.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Editorial review by Doc. dr. sc. Danijel Jerković-Štil, Assistant Professor, FERIT Osijek.