A portable heater says 2,000 watts. Your electricity bill quotes pence per kilowatt hour. A kettle runs for minutes, a fridge cycles all day, and the direct debit takes the same amount every month. It is no wonder appliance costs can feel hard to pin down.
To work out the cost of running household appliances in the UK, you need three things: the energy the appliance uses, how long it runs and the tariff you pay. Once those are in matching units, the arithmetic is straightforward. The harder part is using an honest estimate of real use.
Keep your bill nearby and open the electricity running cost calculator. This guide explains which numbers to enter, how to compare appliances and why an appliance estimate will not equal your whole electricity bill.
Find your own electricity unit rate first
The unit rate is the price of one kilowatt hour, usually written as p/kWh. Look on the bill, tariff information or supplier account. If you have separate day and night prices, the time the appliance runs matters. Public EV charging can have a very different rate from electricity supplied at home.
As a dated reference, Ofgem published a GB average Direct Debit cap electricity unit rate of 26.32p/kWh and a 54.83p daily standing charge for October to December 2026. These figures are not a universal tariff: payment method, region and tariff arrangements matter. Ofgem’s GB reference does not cover Northern Ireland. [1]
Our calculator includes that reference but lets you replace it. Use your actual billed rate for a fixed tariff, a different payment arrangement or a Northern Ireland supply. Check whether the figure already includes any applicable tax; do not add the same amount twice.
For most examples below, we use a rounded hypothetical 25p/kWh to keep the sums easy to follow. That is an arithmetic assumption, not a claim about the current national rate.
Convert watts into kilowatt hours
Watts describe power: how quickly energy is being used at a particular moment. Kilowatt hours describe the quantity of energy used over time. A 1,000-watt appliance is a 1-kilowatt appliance. If it draws that power continuously for one hour, it uses 1kWh.
The basic formula is:
Energy in kWh = watts ÷ 1,000 × hours of operation.
Cost in pounds = energy in kWh × unit price in pence ÷ 100.
A 2,000-watt heater drawing full power for two hours uses 2,000 ÷ 1,000 × 2 = 4kWh. At the hypothetical 25p rate, that is £1. Run it that way for 30 days and the illustrated energy cost is £30.
This is the right calculation for constant draw. If a thermostat switches the heater off for part of the time, actual use is lower than assuming full power throughout. Conversely, leaving it on for longer changes the total even though the rating on the label stays the same.
Worked examples: heaters, kettles and low-power devices
The table assumes each stated wattage is drawn continuously for the stated period. Appliance ratings and daily patterns are invented examples, not typical usage measurements. All costs use the same hypothetical 25p/kWh and exclude standing charges.
| Illustrative use | Energy | Cost |
|---|---|---|
| 2,000W heater for 2 hours | 4kWh | £1.00 |
| 3,000W kettle for 5 minutes total | 0.25kWh | 6.25p |
| 100W device for 8 hours | 0.8kWh | 20p |
| 10W lamp for 5 hours | 0.05kWh | 1.25p |
| 500W appliance for 30 minutes | 0.25kWh | 6.25p |
Notice the kettle. Its power rating is higher than the heater’s, but five minutes of operation uses far less energy than two hours of heating. Comparing watts without comparing time can lead you to focus on the wrong appliance.
When entering minutes in a calculator that asks for hours, divide by 60. Thirty minutes is 0.5 hours; five minutes is about 0.0833 hours. If you boil the kettle several times, total the actual boiling time rather than the time it sits plugged in.
Use measured energy when the power draw changes
Many appliances do not run continuously at their maximum rating. A fridge cycles, a washing machine changes stages and a thermostat controls heating. A label’s maximum input power can be useful for an upper-bound illustration, but it may not be a sensible average for a full day.
If a programme has a quoted or measured kWh-per-cycle figure, that is usually a more relevant starting point than multiplying its highest wattage by the whole cycle duration. Check that the figure relates to the programme you actually use.
A suitable plug-in energy monitor can help with compatible plug-in appliances, provided it is used within its rating and according to instructions. Supplier smart-meter information can help identify household changes, but if several appliances run together it cannot automatically tell you which one caused the increase.
Do not guess about hard-wired equipment or open an appliance to investigate its consumption. Use the manufacturer’s information or ask a qualified professional if you need equipment-specific help.
Separate appliance energy from the whole household bill
Your electricity bill can include standing charges, usage from many appliances, adjustments and other account items. An estimate for one heater is not a prediction of the direct debit. It also says nothing about gas used for heating or hot water.
If you already pay a standing charge for an active supply, the incremental cost of running one extra device is usually the energy it consumes. If you are building a total household budget, standing charges still need to be included once at household level.
At Ofgem’s dated 54.83p daily reference, 30 days would represent about £16.45 in standing charges. That is our multiplication of the published reference, not a charge that applies to every household. [1] Keep your own supply’s figure in the monthly household budget rather than adding it separately to every appliance.
Compare a change in behaviour, not just two appliances
Suppose you are choosing between running the example 2kW heater for two hours or reducing the total full-power time to one hour. At 25p/kWh, the difference is 2kWh, or 50p per day. Across 30 days that is £15, assuming the same power and tariff throughout.
Whether the change is suitable depends on comfort, health and the property. Do not reduce heating in a way that puts someone’s wellbeing at risk. The calculation helps you understand a choice; it does not tell you what temperature or heating schedule is safe for your household.
Try one change at a time in the calculator: shorter use, a lower average power draw or a different tariff. Changing all three at once makes it harder to see which assumption caused the saving. When comparing products, check whether they perform the same task to the same standard.
What about the cost of charging an electric car?
For an EV, the energy added to the battery and energy bought from the charger are not necessarily identical because charging has losses. The EV charging cost calculator includes a charging-efficiency input so the distinction is visible.
For example, adding 36kWh to a battery at an assumed 90% efficiency needs 40kWh from the charger. At an assumed 25p/kWh, the illustrated electricity cost is £10. This excludes parking and session fees. Replace the price for a public charger rather than using a home cap reference.
If you are comparing motoring costs, put the same journey basis into the petrol and diesel fuel calculator. Electricity and fuel are only part of car ownership: insurance, depreciation, maintenance and parking also belong in a full comparison.
A useful routine when a bill rises
- Check that the bill’s period and meter readings make sense.
- Compare the tariff and standing charge with the previous period.
- Look for a change in hours at home, heating, hot water or appliance use.
- Estimate the largest plausible changes before spending time on tiny devices.
- Contact the supplier if the account or readings need explaining.
If paying the bill is becoming difficult, contact the supplier early about the account and available support rather than relying only on small appliance savings. Budget arithmetic is helpful, but it cannot turn an unaffordable essential bill into a manageable one on its own.
Common appliance-cost questions
Can I multiply the direct debit by 12 to find the cost of an appliance?
No. The direct debit covers the supply account, not one device. Use measured or estimated kWh for the appliance and the actual unit rate. Review the household bill separately.
Does a longer low-power programme always cost more?
No. Energy depends on total consumption, not duration alone. A programme with lower average power can run longer and still use less energy. Use programme-specific kWh where available rather than judging only the clock.
Sources and calculation notes
Official information was checked on 16 October 2026. The article’s worked calculations use the stated inputs and assumptions; hypothetical budgets are not market averages. Check current eligibility and product terms before relying on a figure.