Electricity Cost Calculator: Appliance Running Cost
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Electricity Cost Calculator
Work out what any appliance actually costs to run, per hour, day, month and year. The duty cycle field is the one that matters: a fridge rated 150 watts does not draw 150 watts for 24 hours, and ignoring that overstates its cost by more than three times.
kWh = watts / 1000 x hours x duty cycle. Cost = kWh x rate.
Start from a typical appliance
Jump to a common wattage
Annual cost as the tariff moves
What everything else costs, at your rate
How to use this tool
Pick an appliance from the buttons to load a typical wattage, hours and duty cycle, then change any of them to match yours. The single most important field is the rate per kWh, because it moves the answer more than anything else on the page and almost nobody knows theirs off the top of their head. If you do not, switch to the third mode and work it out from a bill.
The wattage is usually printed on a label on the back or underside of the appliance, or on the plug. If it gives amps instead, multiply by your supply voltage: 8 amps at 120 volts is 960 watts, 8 amps at 230 volts is 1840 watts. That is Ohm law doing the work, and it is why the same appliance model carries a different amp rating in different markets.
Why duty cycle is the field everyone skips
The number on the label is what the appliance draws while it is actually running. For a kettle or a heater on full, that is the same as what it draws the whole time it is switched on, so duty cycle is 100 percent and you can ignore it.
Anything with a thermostat is different. A fridge, a freezer, an air conditioner, a heat pump, an immersion heater. These reach their target and switch the compressor or element off, then cycle back on when they drift. Over 24 hours a fridge compressor might run for 7 or 8 of them. That is a duty cycle around 30 percent.
The difference is not small. A 150 watt fridge, priced as though it drew 150 watts for the full 24 hours at 15 cents a unit, comes out at 197 dollars a year. At a realistic 30 percent duty cycle it is 59 dollars. The naive figure is 3.3 times too high, and it is what most online calculators will hand you, because they never ask the question.
If you want the real figure and cannot estimate the duty cycle, a plug in energy monitor left on the appliance for a week will measure it directly. Failing that, the energy label on newer appliances quotes annual kWh under a standard test, which already has the cycling built in.
What the calculation is doing
Divide watts by a thousand to get kilowatts. Multiply by the hours it runs and by the duty cycle, and you have kilowatt hours per day. Multiply that by your rate and you have a daily cost. Everything else on the page is that one line scaled to a month or a year.
A kilowatt hour is not a rate, it is a quantity. One kilowatt sustained for one hour, or two kilowatts for half an hour, or a hundred watts for ten hours. All the same kilowatt hour, all the same money. That is the whole reason the unit exists: it collapses power and time into the single thing you are billed for.
Standing charge sits outside that entirely. It is a fixed daily fee for being connected, and it does not care whether you use anything. That is why it belongs in the annual total but must be taken out before you divide a bill to find your true rate per unit, which is what the third mode does.
A worked check you can repeat on paper
Take the default: a 1500 watt portable heater, 5 hours a day, at 15 cents per kWh.
1500 watts is 1.5 kilowatts. Times 5 hours is 7.5 kilowatt hours a day. At 15 cents that is 1.125 dollars a day. Over 365 days it comes to 410.63 dollars a year, or about 34 dollars a month. For one heater, in one room.
Now the comparison that people actually want. Swap an old 60 watt incandescent bulb running 5 hours a day for a 9 watt LED. The incandescent costs 16.43 dollars a year, the LED costs 2.46, so the saving is 13.96 a year per bulb. If the LED cost 4 dollars it pays for itself in about three and a half months, and after that it is pure return for the rest of its life.
Then the one that surprises people. A single device left on standby drawing 5 watts, 24 hours a day, costs 6.57 dollars a year. That sounds trivial until you count them. Fifteen such devices around a house is nearly a hundred dollars a year for nothing, and the fix is a switched power strip.
Mistakes that catch people out
Leaving duty cycle at 100 for anything with a thermostat. Covered above and worth repeating, because it is the error that produces the most wrong answers by the widest margin.
Using the advertised tariff instead of your real one. Bills carry standing charges, tiered rates, delivery fees and taxes. Divide the whole bill by the units and you get a rate that is often twenty to forty percent above the headline figure. That blended number is the honest one for a running cost estimate.
Assuming a flat rate when you are on time of use. If your utility charges more at peak, the cost depends on when the appliance runs as much as how long. A tumble dryer run at midnight and one run at six in the evening can differ by half. This tool takes a single rate, so use your average, and treat the answer as a mid point rather than a precise figure.
Forgetting that heating is nearly always the biggest number. People obsess over phone chargers and leave a 1500 watt heater running. The bar chart above is roughly to scale: an EV charger, a heat pump and a portable heater are in a different league from everything electronic in the house combined.
Ignoring the days in use. A pool pump or an air conditioner might run hard for four months and not at all for eight. Set the days per year field to the season rather than 365, or the annual figure will be roughly three times what you actually pay.
How this was checked
The engine was written twice and the two versions compared on the same cases. A 1500 watt load for 5 hours a day at 15 cents returns 1.125 dollars a day and 410.63 a year. A 60 watt bulb for 8 hours returns 26.28 a year. A 150 watt fridge returns 197.10 at 100 percent duty and 59.13 at 30 percent, an overstatement factor of 3.33.
The reverse direction was checked too: a 120 dollar bill for 800 kWh returns a rate of exactly 0.15 per kWh, and adding a 45 cent daily standing charge to 500 kWh over 30 days returns 88.50. Round trips through every combination of wattage, hours and duty cycle recover the original wattage to within one part in a billion. Every figure in the appliance table and in the diagram is generated by the same functions the calculator uses, so none of them can drift from the tool.
Popular running costs
Each link opens the tool with that wattage loaded at the default 5 hours a day and 15 cents per kWh. Change the rate to yours as soon as it opens, because that is the number that moves the answer most.
Cost to run by wattage. 5 W a day · 9 W a day · 10 W a day · 15 W a day · 20 W a day · 25 W a day · 30 W a day · 40 W a day · 50 W a day · 60 W a day · 75 W a day · 100 W a day · 120 W a day · 150 W a day · 200 W a day · 250 W a day · 300 W a day · 400 W a day · 500 W a day · 600 W a day · 750 W a day · 800 W a day · 1,000 W a day · 1,200 W a day · 1,500 W a day · 1,800 W a day · 2,000 W a day · 2,200 W a day · 2,400 W a day · 2,500 W a day · 3,000 W a day · 3,500 W a day · 4,000 W a day · 4,500 W a day · 5,000 W a day · 6,000 W a day · 7,200 W a day · 9,600 W a day · 11,000 W a day
A 1,500 W heater on different daily hours. 1,500 W for 1 h a day · 1,500 W for 2 h · 1,500 W for 4 h · 1,500 W for 6 h · 1,500 W for 8 h · 1,500 W for 12 h · 1,500 W for 24 h
Appliances that cycle, with a realistic duty. fridge freezer at 30 pct duty · chest freezer at 35 pct duty · window air conditioner at 60 pct duty · heat pump at 45 pct duty · hot water tank at 25 pct duty
The same 1,500 W heater on different tariffs. at 0.08 per kWh · at 0.1 per kWh · at 0.12 per kWh · at 0.15 per kWh · at 0.18 per kWh · at 0.22 per kWh · at 0.25 per kWh · at 0.3 per kWh · at 0.35 per kWh · at 0.4 per kWh
Related Calculators and Reference
- Energy converter turn kilowatt hours into joules, BTU and calories when you are comparing electricity against gas or fuel.
- Watts to lumens calculator before you cut lighting wattage, check you are not also cutting the light you need.
- Battery capacity calculator for anything running off a pack rather than the wall, including how long it lasts under a given load.
- Ohm law calculator turn an amp rating on a label into watts, which is what this page needs.
- R value and RSI converter the cheapest way to cut a heating bill is usually insulation rather than a different heater.
- Three phase power calculator for commercial and industrial loads, where power factor changes what you are billed.
- BTU Calculator: air conditioner size for a room in BTU and tons.
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- Gas Cost Calculator: fuel cost of a trip, per person and per mile.
- EV Charging Time and Cost Calculator: the cost of a charge once losses are counted.
- US EIA average retail electricity price by state is a good reality check on the rate you enter, though your own bill is always the better source.