What this calculator works out
This calculator turns a wattage into money: the energy one use consumes, what that costs, and what it adds up to across a year.
The annual figure is the one worth looking at. Fifty pence a use sounds trivial; a hundred pounds a year is a decision.
It also asks for something most running-cost calculators leave out. Appliances with a thermostat — fridges, freezers, ovens, heaters — do not draw their rated power the whole time they are switched on, and assuming they do can overstate the cost threefold. The duty cycle field corrects for that.
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Before you calculate
- Find the wattage on the rating plate — on the back or underside, or inside the door on white goods. It may be given as volts and amps, which multiply together to give watts.
- Use the unit rate from a recent bill in pence per kilowatt-hour, not a national average.
- Hours per use means actual running time, which for a washing machine or dishwasher is the cycle length.
- Set the duty cycle honestly. Nameplate wattage is the maximum draw, and anything with a thermostat spends much of its time well below it.
A fridge is powered around the clock — switch it off and the food spoils — but its compressor is not running around the clock. The thermostat switches it on and off, typically for a third to a half of the time. Multiply the nameplate figure by 24 hours and you can overstate the cost threefold. The same applies to freezers, ovens, immersion heaters and any thermostatic heater. Kettles, toasters, hair dryers, lighting and televisions do not cycle, so watts × hours is fair for those.
How this calculator works
Watts to kilowatt-hours, then to money:
Energy per use = watts × hours × duty cycle ÷ 1,000
Cost per use = energy × price in pence ÷ 100
Annual cost = cost per use × uses per week × 52A watt measures power, the rate at which energy is used. A kilowatt-hour (kWh) measures energy: power multiplied by time. One kilowatt-hour is what a 1,000 W appliance uses in an hour, or a 100 W appliance uses in ten hours. Your meter counts kilowatt-hours and your supplier charges a set price for each one. On a bill they are often just called units.
The duty cycle is the share of running time an appliance spends actually drawing its rated power. It is the single largest source of error in running-cost estimates, and most calculators ignore it entirely.
Standby is added separately, across the hours the appliance is not in use, because a device drawing two watts for 8,760 hours a year is not negligible even though two watts sounds like nothing.
The standing charge is deliberately excluded. It is a fixed daily amount — 57.19p a day on average under the current cap, around £209 a year — payable whether or not you switch anything on. It belongs to the property rather than to any one appliance, so including it would make every appliance look more expensive than it is and would make comparisons meaningless.
For fridges, freezers, washing machines and dishwashers, the annual kWh figure on the energy label is more reliable than anything calculated from a nameplate, because it comes from standardised testing that already accounts for cycling.
Worked example: a tumble dryer
A vented tumble dryer rated at 2,500 W. A full load takes about an hour and a half and the household runs four loads a week. The heating element is on for essentially the whole cycle, so the duty cycle is 100%.
- Energy per cycle: 2,500 ÷ 1,000 × 1.5 = 3.75 kWh
- Cost per cycle: 3.75 × 26.11p = 98p
- Across a year: 3.75 × 4 × 52 = 780 kWh, or £203.66
Ninety-eight pence a load is easy to ignore. Two hundred pounds a year is not, and it is close to a fifth of a typical household's entire annual electricity use from one appliance. Drying two loads a week on a rack instead would save around £100 a year.
Worked example: a fridge-freezer, done both ways
This is the example that shows why the duty cycle matters. A fridge-freezer with a 100 W rating plate, powered 24 hours a day.
- Ignoring the duty cycle: 100 ÷ 1,000 × 24 = 2.4 kWh a day, or about 874 kWh a year. At 26.11p that is £228.10 a year — which would make it the most expensive appliance in most homes.
- With a realistic 35% duty cycle: 0.84 kWh a day, or 306 kWh a year, which is £79.83 a year.
The Energy Saving Trust puts the running cost of an F-rated 424-litre fridge-freezer at around £80 a year in Great Britain. The duty-cycle method lands on the right answer. The naive one is nearly three times too high.
If the appliance has a thermostat and you have its energy label, use the label figure. If you do not have the label, use a duty cycle and treat the answer as a broad estimate rather than a number to make decisions on.
Understanding the result
The annual figure is the one worth looking at. Costs per use are reassuringly small and encourage you to ignore them. A year is the timescale on which small amounts turn into real money.
| Annual cost | What it means | Worth acting on? |
|---|---|---|
| Under £10 | Negligible | No. Chasing it costs more effort than it saves. |
| £10 to £50 | Modest | Only if the change is easy or free. |
| £50 to £150 | Significant | Yes. Worth changing how you use it. |
| Over £150 | Major | Yes. Worth considering replacement, not just habit. |
Running cost alone does not justify replacement. If a new appliance costs £500 and saves £60 a year, the payback is over eight years, possibly longer than it will last. Replacing something that still works also carries an environmental cost that no running-cost calculation captures.
Typical power ratings and duty cycles
Starting points only, for when you cannot find the rating plate.
| Appliance | Typical watts | Duty cycle | Notes |
|---|---|---|---|
| Kettle | 3,000 | 100% | Cost is driven by how much water you boil |
| Electric oven | 2,100 | 60% | Cycles once up to temperature |
| Air fryer | 1,500 | 70% | Smaller cavity, shorter times |
| Microwave | 1,200 | 100% | Input power is higher than the quoted cooking power |
| Washing machine | 2,100 | 35% | Heating water dominates; 30 °C costs far less than 60 °C |
| Dishwasher | 1,800 | 35% | Eco cycles are longer but cheaper |
| Tumble dryer, vented | 2,500 | 100% | Among the most expensive appliances to run |
| Tumble dryer, heat pump | 900 | 70% | Slower, roughly half the energy |
| Fridge-freezer | 100 | 35% | Use the energy label figure if you have it |
| Chest freezer | 150 | 30% | Fuller freezers cycle less |
| Electric shower | 8,500 | 100% | Very high power, very short use |
| Immersion heater | 3,000 | 100% | Thermostat cuts out at temperature |
| Fan heater | 2,000 | 60% | Depends heavily on the thermostat setting |
| Desktop computer | 200 | 60% | Varies enormously with what it is doing |
| Television, 55-inch LED | 100 | 100% | Brightness settings make a real difference |
| Broadband router | 10 | 100% | Small, but on 8,760 hours a year |
| LED bulb | 9 | 100% | Replaces a 60 W filament bulb |
Things that affect the result
- Duty cycle. The largest single source of error.
- Room temperature. A fridge or freezer in a warm kitchen or an unheated garage works considerably harder than one at a steady 20 °C.
- Age and condition. Worn door seals, dusty condenser coils, furred kettle elements and clogged dryer filters all increase consumption.
- Programme settings. Almost all of a washing machine's electricity goes into heating water, so the temperature you choose matters more than anything else.
- Load size. Half-empty dishwashers and dryers cost nearly as much to run as full ones.
- Your actual unit rate. Rates vary by region, meter type and payment method, and the cap is reviewed every three months.
- Rounding. Treat the result as accurate to the nearest few pounds, not the nearest penny.
Common mistakes
- Multiplying a fridge's rating plate by 24 hours. The classic error, and it produces an answer around three times too high.
- Confusing watts with kilowatts. A 2 kW appliance is 2,000 W. Forgetting to divide by 1,000 gives an answer a thousand times too large.
- Entering pounds where pence are expected. Enter 26.11, not 0.2611.
- Counting time plugged in rather than time running. A washing machine plugged in all week runs for perhaps five hours of it.
- Using a microwave's cooking power as its input power. An 800 W microwave draws roughly 1,200 W from the socket.
- Including the standing charge. It is payable whether or not you use anything.
- Treating the estimate as exact. Two identical models in two different kitchens will not cost the same to run.
Frequently asked questions
How accurate is this calculator?
For appliances drawing steady power — kettles, lighting, televisions, hair dryers — it is accurate to within a few per cent provided your wattage and hours are right. For anything thermostatic, accuracy depends entirely on the duty cycle you enter, and plus or minus 30% is a realistic range. The annual figure from an energy label is considerably more reliable. For a genuinely accurate answer, use a plug-in energy monitor over a week or two.
Where do I find an appliance's wattage?
The rating plate, usually on the back, base or inside the door. Some list volts and amps instead — multiply them for watts, so 230 V at 10 A is 2,300 W. For appliances that cycle, the energy label's annual consumption figure is more useful than the nameplate.
What duty cycle should I use if I do not know?
Use 100% for anything that heats without a thermostat or runs at constant load. Use 30 to 40% for fridges and freezers, 50 to 70% for thermostatic heaters and ovens, and around 35% for washing machines and dishwashers across a full cycle. The table on this page gives starting points. If precision matters, measure rather than guess.
Should I use the wattage or the kWh per year from the label?
The kWh per year whenever you have it. It comes from standardised testing that already accounts for cycling, which is exactly the thing hardest to estimate. Divide it by 365 to get a daily figure. Use the wattage method when there is no label, or when your use differs substantially from the test conditions.
Why is my answer different from my electricity bill?
This calculator covers one appliance, while your bill covers the whole house. It excludes the standing charge, which is roughly £209 a year on its own. Your unit rate may differ from the default. And if your bill is based on an estimated reading rather than an actual one, it may not reflect what you have really used.
Where does the default electricity price come from?
It is Ofgem's price cap average for Great Britain for customers paying by Direct Debit: 26.11p per kWh for 1 July to 30 September 2026, including VAT. The cap is reviewed quarterly and the next level is due to be announced by 26 August 2026. Your own rate depends on your region, meter type and tariff, so replace it with the figure from your bill.
Do appliances use power when switched off?
Many do. Anything with a remote, a clock, a standby light or a network connection draws a small amount continuously. A device drawing two watts uses about 17.5 kWh a year, or roughly £4.60. Across a whole household the Energy Saving Trust estimates the total at around £35 a year. Enter a standby figure above to include it.
Is it cheaper to run appliances at night?
Only on a time-of-use tariff such as Economy 7 or an EV tariff, where the unit rate genuinely differs. On a standard single-rate tariff the price is identical at every hour. Check which tariff you are on before rescheduling anything.
Can I use this for gas appliances?
No. Gas is metered by volume and converted to kilowatt-hours using a calorific value, and it is priced separately — currently 7.33p per kWh under the cap, against 26.11p for electricity. Comparing a gas hob with an electric one needs both rates and an allowance for their different efficiencies.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
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References
These organisations publish the guidance and figures behind this page.
- Ofgem — energy price cap unit rates and standing charges — the source of the 26.11p per kWh unit rate and 57.19p daily standing charge used here, for 1 July to 30 September 2026
- Energy Saving Trust — what appliances drive up energy bills — published running costs for fridge-freezers, laundry appliances and standby power
- GOV.UK — energy labelling rules, efficiency schemes and help with energy costs
Unit rates are reviewed quarterly by Ofgem. If the review date above is more than three months old, check the current figure at the source before relying on the default.