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Everyday maths / Free tool

Electricity running cost calculator

Estimate appliance energy use and cost using your own electricity rate.

Your numbersLive result
Choose the question you want to answer.
Display only. No currency conversion.
Required. 0 or more. Use up to 6 decimal places, without commas or currency symbols.
Required. 0 or more. Maximum 24. From 0 to 24.
Required. 0 or more. Whole numbers only. Maximum 36,600. Whole days.
Required. 0 or more. Whole currency units: 0.25 means 25p in GBP.

Example values are prefilled. Change any number to calculate.

Estimated electricity cost

£3.00

Total energy
12 kWh
Energy cost per day
£0.10

Watts ÷ 1,000 × hours gives kWh. Enter the tariff in whole currency units: 0.25 means 25p when GBP is selected. Assumes constant power while running; excludes standing charges and time-of-use tariff changes.

Your inputs stay in this browser.

The working behind the answer

How to use this calculator

Use the appliance’s running power in watts and estimate how long it operates each day. Enter the number of days and your own price per kWh. A tariff shown in pence must be divided by 100 before entering it as GBP.

The formula

Estimate appliance usage

Energy in kWh = watts ÷ 1,000 × hours per day × days; cost = kWh × rate

A worked example

A 100W appliance used 4 hours a day for 30 days consumes 12kWh. At £0.25 per kWh, that costs £3 in energy charges.

Good to know

Assumes constant consumption while running. Thermostats, standby usage and variable power can change real use. Standing charges and time-of-use tariff changes are excluded. The calculator does not look up supplier prices.

Common questions

Can I enter power in kilowatts?

Multiply kilowatts by 1,000 to enter watts: 2kW becomes 2,000W.

Does this include standing charges?

No. It estimates the energy charge for the entered appliance usage only.