Guidance only — always verify against current standards and manufacturer instructions.
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This calculator works out what an electrical appliance costs to run. Enter the appliance's power rating in kilowatts, how many hours a day it runs and your electricity tariff in pence per kWh, and it returns the cost per day, per week and per year.
It is useful for tradespeople who get asked the question on site all the time: what will this heater, immersion, hot tub or tumble dryer actually cost the customer? Being able to give a straight answer — per day and per year — helps customers make sensible decisions about the kit you install.
The maths is simple energy billing: kilowatts multiplied by hours gives kilowatt-hours, and each kilowatt-hour is charged at the tariff rate. The calculator does the unit handling (pence to pounds) and the weekly and annual projections for you.
Cost per day (£) = kW × hours × tariff (p/kWh) ÷ 100
Power in kilowatts multiplied by running hours gives the energy used in kWh. Multiplying by the tariff in pence per kWh gives the daily cost in pence, and dividing by 100 converts it to pounds. Weekly cost is the daily figure times 7, and yearly cost is the daily figure times 365.
Type the appliance's power rating in kW. You will find it on the rating plate or data sheet — for example, a 3 kW immersion heater or a 2 kW fan heater. If the rating is in watts, divide by 1,000 first.
Enter how many hours a day the appliance actually runs. The default is 2 hours. For thermostatically controlled appliances, use the time the element is actually drawing power, not the time it is switched on.
Enter the electricity unit rate in pence per kWh from the customer's bill. The default is 27 p/kWh — replace it with the actual rate, as tariffs vary by supplier and region.
The calculator shows the running cost per day, per week (day × 7) and per year (day × 365), all in pounds.
The result covers unit-rate energy cost only. It does not include the daily standing charge, which the customer pays regardless of usage, and it does not model appliances that cycle on and off under thermostatic control. For a heater with a thermostat, the real cost is usually lower than a flat hours-per-day figure suggests, because the element is not drawing full power the whole time.
Tariffs change often, so always take the unit rate from a current bill rather than assuming a typical figure. If the customer is on an off-peak tariff such as Economy 7, run the calculation separately for the peak and off-peak rates and hours.
The annual figure assumes the same usage every day of the year. Seasonal appliances such as heaters or dehumidifiers will not run year-round, so scale the daily or weekly figure by the months of actual use instead.
Multiply the appliance's power in kW by the hours it runs, then by your electricity unit rate in pence per kWh, and divide by 100 to get pounds. For example, a 3 kW heater running 2 hours a day at 27 p/kWh costs 3 × 2 × 27 ÷ 100 = £1.62 per day.
It depends on your supplier, tariff and region, and rates change regularly. Check the unit rate on a recent bill and enter that figure into the calculator — the default of 27 p/kWh is only a placeholder.
No. The calculator covers the unit-rate cost of the energy the appliance uses. The standing charge is a fixed daily fee you pay whether or not you use any electricity, so it is not part of an individual appliance's running cost.
Look at the rating plate on the appliance or its data sheet. Ratings are given in watts (W) or kilowatts (kW) — divide watts by 1,000 to get kW. For example, a 2000 W appliance is 2 kW.
Thermostats and duty cycles mean many appliances do not draw full power for the whole time they are on, so real usage is often lower. Your bill also includes the standing charge and every other appliance in the property, and tariff rates may have changed since you last checked.
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