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What The Energy Cost Calculator Works Out
- Per day: watts divided by 1,000 to get kilowatts, multiplied by hours of use to get kilowatt-hours, multiplied by your unit rate. A 2kW heater on for two hours uses 4 kWh, about GBP 1.05 a day at the current cap; a 10W LED bulb on for four hours costs about 1p.
- Per month and per year: the daily cost scaled to 365 days, with a month taken as one twelfth of a year. Anything that makes heat (kettles, heaters, ovens, tumble dryers at 2kW to 3kW) is expensive to run; electronics are cheap.
- Electricity unit rate: defaults to the Ofgem price cap average, which is temporarily VAT-free from October 2026 to March 2027. Your bill shows your exact rate; fixed deals and regional rates differ by a few pence.
- Duty cycle (advanced): the share of the time the appliance actually draws its rated power. Thermostat-controlled kit (fridges, heaters, washing machines) cycles on and off, so a 2kW washing machine typically uses 0.5 to 1 kWh a cycle rather than 2 kWh an hour. A cheap plug-in energy monitor gives the true figure.
- Number of appliances and days per week (advanced): multiply the cost for several identical items and scale the annual figure for things used only on some days, such as a tumble dryer on three wash days.
- Off-peak share and rate (advanced): moves part of the use onto a cheaper night rate. Economy 7 and EV tariffs typically charge 7p to 16p overnight, so running a dishwasher or washing machine on a timer can halve its cost.
- Standing charge per year (advanced): the daily fixed charge multiplied by 365, around GBP 200 a year at the current cap. It is shown separately because it is paid once per home, not per appliance.
- Electricity used per year (advanced): annual kilowatt-hours compared with Ofgem's typical household figure of 2,700 kWh, which shows how big a slice of a normal bill one appliance takes.
- Replacement saving and payback (advanced): the running cost of a more efficient appliance at the same hours, the annual saving against the current one, and how many years a given purchase price takes to pay back. A GBP 300 A-rated fridge freezer replacing a 15-year-old one often pays back within four or five years.
Source and further reading: Ofgem: energy price cap.