Start with the units
Power in watts tells you the rate of energy use. Divide by 1,000 for kilowatts, then multiply by hours for kilowatt-hours. A 2,000 W appliance running continuously for two hours uses 4 kWh.
Use your actual tariff
Multiply energy by the VAT-inclusive unit rate on your bill. At an illustrative 25 p/kWh, 4 kWh costs £1. This is a worked example, not a statement of today’s UK tariff. Split use across separate calculations if the rate changes during the day.
Allow for cycling and variable power
A thermostat-controlled heater, fridge or heat pump does not necessarily draw its maximum rated power continuously. Where possible, use measured consumption over a representative period. Avoid judging annual costs from a short unusual period.
Keep the standing charge separate
A standing charge is part of having the electricity supply. It is not normally caused by switching on one additional appliance. Keep it in your household bill budget, while using the running-cost tool to compare changes in appliance use.
Sources & methodology
This page uses original budgeting guidance and transparent arithmetic. Example prices are chosen illustrations, not a survey of UK market prices. Replace them with written quotations.
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