About this calculator
Enter the power of an appliance in watts, how many hours a day you use it and your price per kWh (in pence), and see the running cost per day, month and year.
It stores no tariff and assumes nothing: use the rate from your own bill.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
A 2 kW electric heater, 3 hours a day at 28p
- Cost per month (30 days)
- £50.40
- Cost per day
- £1.68
- Cost per year
- £613.20
- Energy per day
- 6 kWh
- Energy per year
- 2,190 kWh
A 2,000 W appliance used 3 hours a day uses 6 kWh a day and costs £50.40 a month at 28p per kWh.
Show the working
- Energy per day = watts ÷ 1,000 × hours = 2,000 ÷ 1,000 × 3 = 6 kWh.
- Cost per day = kWh × price = 6 × 28p = £1.68.
- Per month (30 days): £50.40. Per year (365 days): £613.20.
A 10 W LED bulb on for 6 hours at 28p
- Cost per month (30 days)
- £0.50
- Cost per day
- £0.02
- Cost per year
- £6.13
- Energy per day
- 0.06 kWh
- Energy per year
- 21.9 kWh
A 10 W appliance used 6 hours a day uses 0.06 kWh a day and costs £0.50 a month at 28p per kWh.
Show the working
- Energy per day = watts ÷ 1,000 × hours = 10 ÷ 1,000 × 6 = 0.06 kWh.
- Cost per day = kWh × price = 0.06 × 28p = £0.02.
- Per month (30 days): £0.50. Per year (365 days): £6.13.
A 150 W TV for 5 hours at 25p
- Cost per month (30 days)
- £5.63
- Cost per day
- £0.19
- Cost per year
- £68.44
- Energy per day
- 0.75 kWh
- Energy per year
- 273.75 kWh
A 150 W appliance used 5 hours a day uses 0.75 kWh a day and costs £5.63 a month at 25p per kWh.
Show the working
- Energy per day = watts ÷ 1,000 × hours = 150 ÷ 1,000 × 5 = 0.75 kWh.
- Cost per day = kWh × price = 0.75 × 25p = £0.19.
- Per month (30 days): £5.63. Per year (365 days): £68.44.
How the cost is worked out
Electricity is billed in kilowatt-hours (kWh): 1 kWh is 1,000 watts used for one hour. Energy per day = watts ÷ 1,000 × hours. Cost = kWh × your price per kWh. A 2,000 W heater used for 3 hours uses 2 × 3 = 6 kWh.
Finding the wattage
The power is usually printed on the appliance's label or plate. Some appliances cycle on and off (fridges, kettles, ovens), so the average is lower than the label's maximum; use a smaller number of hours to reflect the time they are actually drawing power.
Your price per kWh
Find it on your electricity bill or in your supplier's app, listed as a unit rate in pence per kWh. Rates change, so check it when you use the calculator. The standing charge is a separate daily fee and is not included here.
Frequently asked questions
How do I calculate what an appliance costs to run?
Multiply its power in kilowatts by the hours used, then by your price per kWh.
What is a kWh?
A kilowatt-hour: 1,000 watts used for one hour.
Does it include the standing charge?
No, only the energy used by the appliance.
Why do my results differ from my bill?
Appliances cycle on and off and rates change, so the result is an estimate based on the numbers you enter.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.