UK money
Heater and appliance running cost
Watts and hours at the Ofgem unit rate, with the standing charge kept separate.
Last updated: October 2026
How to use it
- Pick a preset, or type the watts printed on the appliance.
- Enter the hours it runs on a typical day. A kettle’s three minutes is 0.05 of an hour.
- Leave the unit rate at the Ofgem Direct Debit average, or type the pence per kWh on your bill. The standing charge is shown beside the appliance cost.
How it's calculated
Energy in a hour is watts divided by 1,000. Cost is that figure times the unit rate, in pence, rounded to the nearest penny. A day is the hourly cost times the hours you enter. A longer stretch multiplies the daily energy by the number of days. The default stretch is 30 days, which is an illustration, not a calendar month.
The standing charge is 54.83p a day at the default, times the same number of days, and it is not added into the appliance cost. You pay it whether or not the heater is on. The default unit rate is 26.32p per kWh, the Ofgem average for a Direct Debit customer in England, Scotland and Wales from 1 October to 31 December 2026. Electricity on the cap has no VAT from 1 October 2026 to 31 March 2027. Your region and payment method can differ, so the rate box is editable. Northern Ireland is outside this cap.
Worked examples
A 2 kW fan heater for one hour uses 2 kWh. At 26.32p that is £0.53 an hour.
The same heater for 4 hours a day over 30 days uses 240 kWh and costs £63.17. The standing charge for those 30 days is £16.45, shown separately.
A 100 W electric blanket for 8 hours a day over 30 days costs £6.32. A 3 kW kettle for three minutes (0.05 hours) costs £0.04 for that boil. Preset watts are typical nameplates. Use the number on the appliance.
Sources
Ofgem: price cap, 1 October to 31 December 2026, Ofgem: unit rates and standing charges. The £1,723 figure on those pages is a typical dual-fuel bill, not the cost of a heater.
I check these figures after each Budget or Finance Act and when a rate changes. The calculation runs in this browser. Nothing you type is stored or uploaded. Corrections: [email protected].
Questions
Is this the most I can be charged?
No. The cap limits the unit rate and standing charge on a default tariff in Great Britain. A fixed tariff can be different. The amount you pay still depends on how long the appliance runs.
Why is the standing charge separate?
The standing charge is a daily amount for the supply. Putting it inside a one-hour heater cost would make that hour look far more expensive than the electricity the heater used.
Does the figure include VAT?
The default electricity rate is the Ofgem Direct Debit average with no VAT, which is how Ofgem states electricity from 1 October 2026 to 31 March 2027. If your bill shows a different rate, type that rate.
Can I use this for gas heating?
No. The sums are for an electrical appliance. Ofgem’s gas rate for the same quarter is a different figure and still includes 5% VAT.
Are my numbers stored?
No. The watts, hours and rate stay in this browser. Nothing is uploaded.