Electricity Cost Calculator
Find what any appliance costs to run, from its wattage, how much you use it, and the rate on your bill.
Typical figures to start from — edit any field below and the preset becomes Custom.
On your bill, often as cents per kWh — 17¢ is 0.17.
1.2 kWh a day, 7 days a week, at $0.17/kWh = $74.46 a year
The week, month and year assume this pattern of use carries on. For something seasonal — air conditioning, a space heater — take the monthly figure and multiply by the months it actually runs.
Electricity is billed by the kilowatt-hour: one kilowatt (1,000 watts) drawn for one hour. That makes the cost of running anything a single multiplication — power, times time, times the rate on your bill. This calculator does it for a day, a week, a month and a year at once, because the yearly figure is usually the one that changes a decision and the daily figure is usually the one that sounds harmless.
The formula
Cost = (watts ÷ 1,000) × hours × rate. A 1,000 W appliance run for one hour uses exactly 1 kWh, which is the definition of the unit. So a 1,500 W space heater running five hours a day uses 7.5 kWh, and at 17¢ per kWh that is $1.28 a day. Run it every day for a month and it is $38.78; leave it running all year and it is $465.38.
The wattage is printed on the appliance itself — on the nameplate, a sticker on the back or base, or the power brick. If it is given in kilowatts, multiply by 1,000: a 3.5 kW air conditioner is 3,500 W. If the label gives only amps and volts, multiply them: 12 A at 120 V is 1,440 W.
The rate is on your electricity bill, usually quoted in cents per kWh — enter 17¢ as 0.17. Use the total cost of your bill divided by the kWh it billed, not just the headline energy charge: delivery, transmission and fixed charges can be a third to a half of what you actually pay, so the "all-in" rate is the honest number for a decision about whether to run something.
Days per week, and why it matters
Most usage isn't daily. A dryer might run three times a week, an oven four, an iron once. The Days/week field prorates the longer periods without touching the daily figure, so the "per day it runs" row stays a true picture of one use and the month and year reflect how often that use actually happens. A 3,000 W electric dryer running an hour three times a week is 3 kWh — 51¢ — per load, but $6.65 a month and $79.78 a year.
A month here is a twelfth of a year (30.4 days), not 30 days. That is deliberate: it makes twelve of the monthly figures add up to exactly the yearly one, which they would not if the month were rounded.
Reading the appliance presets
The presets are typical figures to start from, and the wattage and the hours have to be read together. For anything thermostatically controlled — a refrigerator, a freezer, a water heater, an air conditioner — the wattage given is what it draws while the compressor or element is actually running, and the hours are how long that is, not how long the appliance is switched on. A fridge is plugged in 24 hours a day but its compressor runs perhaps eight, so the preset is 150 W for 8 hours: 1.2 kWh a day, $74.46 a year. Entering 150 W for 24 hours would triple that and be wrong.
The seasonal presets have the opposite trap, at the other end. Central air conditioning at 3,500 W for eight hours a day is $144.78 a month, which is realistic for a hot month — but the year row extends that across all twelve, giving $1,737.40, and almost nobody runs air conditioning in February. For seasonal loads, read the monthly figure and multiply it yourself: four months of cooling is about $579, and three months of that space heater is about $116.
Worked examples
- Refrigerator. 150 W while the compressor runs, 8 hours a day, every day. 1.2 kWh/day, 36.5 kWh/month, 438 kWh/year — $6.21 a month, $74.46 a year.
- Wi-Fi router left on permanently. 10 W for 24 hours is only 0.24 kWh a day, or 4¢ — but it never stops, so it is 87.6 kWh and $14.89 a year. This is the shape of every always-on device: trivial per day, real per year.
- An LED bulb versus an incandescent. Five hours a day: the 10 W LED costs $3.10 a year, the 60 W bulb it replaced costs $18.62. The $15.52 difference per bulb per year is why the swap pays for itself in months, and it multiplies by every fitting in the house.
- Electric clothes dryer. 3,000 W for an hour, three times a week. 3 kWh a load — 51¢ — and $79.78 a year. Line-drying half your loads saves about $40.
- Desktop PC and monitor. 200 W for six hours, five days a week. 1.2 kWh a working day, $53.19 a year. Sleeping it instead of leaving it idle overnight is most of that.
- EV charging at home. A 7.2 kW Level 2 charger for two hours, four nights a week, is 14.4 kWh a session — $2.45 — and $510.58 a year. Compare that against the gasoline it replaces rather than against your other appliances.
- Phone charger. 5 W for three hours is 0.015 kWh, or about a quarter of a cent a day: 93¢ a year. Worth knowing so you can stop worrying about it and go look at the water heater instead.
Where the money actually is
Running the numbers on a few appliances tends to reorder people's intuitions. Heating and cooling anything — air, water, or a room — dominates, because turning electricity into heat takes kilowatts, while electronics take watts. An electric water heater at 4,000 W for three hours a day is $62.05 a month; every phone charger in the house together is a rounding error against it. The rule of thumb is that if an appliance makes something hot or cold, it is worth calculating, and if it makes light or sound, it usually isn't.
The second thing the numbers show is that duration beats wattage more often than people expect. A 10 W router running permanently costs more per year than a 1,500 W hair dryer used for a quarter of an hour a day. Anything that never switches off deserves a look even when its wattage looks trivial.
What this doesn't cover
This is a single-appliance estimate at a flat rate. It does not model time-of-use tariffs, where the rate changes by hour — if you are on one, run the calculator once per rate band with the hours that fall in it. It does not handle tiered rates, where the price per kWh steps up after a monthly threshold; in that case use your marginal (highest) rate, since anything extra you run is billed at the top of the tier. It ignores standby draw, the watt or two an appliance uses while off, which is small per device but adds up across a house. And it assumes the appliance draws its rated power whenever it is on, which is true of a heater or a kettle and only roughly true of a computer or a television.
How do I calculate the cost of running an appliance?
Divide the wattage by 1,000 to get kilowatts, multiply by the hours you run it, and multiply by your rate per kWh. A 1,500 W space heater for 5 hours is 7.5 kWh, and at 17 cents per kWh that is $1.28 a day. This calculator does that arithmetic and extends it to a week, a month and a year.
How much does it cost to run a refrigerator for a year?
About $74 at 17 cents per kWh, for a typical modern 18 cu ft fridge. The wattage looks like 150 W, but the compressor only runs about a third of the time, so the daily consumption is around 1.2 kWh rather than 3.6. An older or larger fridge can easily double that — at 250 W and 10 hours of compressor time a day it is $155 a year, which is what makes replacing a garage second fridge pay off.
How much electricity does leaving a light on cost?
It depends entirely on the bulb. A 10 W LED left on for five hours a day costs $3.10 a year at 17 cents per kWh. The 60 W incandescent it replaced costs $18.62 for the same five hours. Leaving an LED on all night is genuinely cheap; leaving incandescent or halogen fittings on is not.
What is a kilowatt-hour?
A kilowatt-hour is the energy used by a 1,000 W appliance running for one hour, and it is the unit your electricity is billed in. A 100 W device would take ten hours to use one; a 2,000 W kettle uses one in half an hour. Watts measure the rate of draw at any instant, kilowatt-hours measure the total consumed over time, and only the second one appears on your bill.
What electricity rate should I use?
Take it from your own bill rather than an average, and use the all-in rate: divide the total amount you paid by the number of kWh billed. That folds in delivery, transmission and fixed charges, which are often a third or more of the bill. The 0.17 default here is roughly the recent US residential average, but the real figure ranges from under 11 cents to over 40 cents depending on where you live.
Why does the calculator ask for days per week?
Because most appliances are not used daily, and a monthly figure that assumes they are will be badly wrong. A dryer run three times a week costs a third of what it would cost run every day. The daily row always shows one day of actual use; the week, month and year rows are prorated by how often that happens.
How do I work out the cost for something seasonal, like air conditioning?
Read the monthly figure and multiply it by the number of months you actually run it, rather than using the yearly row. The yearly row assumes the usage pattern you entered continues all twelve months, which is right for a fridge and wrong for a space heater. Central air at 3,500 W for eight hours a day is about $145 a month, so a four-month cooling season is around $579.
How can I find the wattage of an appliance?
Check the nameplate — a sticker or stamped plate on the back or base, or on the power supply. Kilowatts multiply by 1,000 to get watts. If only amps and volts are listed, multiply them: 12 A at 120 V is 1,440 W. Nameplate ratings are maximums, so for anything that modulates its draw (a computer, a TV, a variable-speed motor) a $20 plug-in energy meter gives a much better number than the label does.