Appliance Running Cost Calculator

The sums are simple and almost everybody does one of them wrong. Watts are not kilowatt-hours until you multiply by time and divide by a thousand. A tariff in pence is not pounds. And the standing charge is there whether the appliance is on or not, which is how “it only costs pennies” and “the bill is enormous” can both be true at once.

Start from a typical appliance

Power in watts

Off the plate on the appliance.

Hours a day it runs

While it is actually drawing power.

Days a week

Between 1 and 7.

Tariff, pence a unit

Pence per kilowatt-hour, from the bill.

Standing charge, pence a day

Charged whether you use anything or not.

Replacement's power in watts

0 to skip the payback sum.

What the replacement costs, in pounds

Used only for the payback.

£364 a year

4 units each time it runs, 100p a go, 1456 units a year. With the standing charge the electricity bill for this comes to £583.

✓ The cost divides back into units, and the units back into watts — 100p at 25p a unit is 4 units, which is 2000W for 2 hours
✓ Watts became kilowatt-hours by dividing by a thousand — 2000W for 2h is 4 units, not 4000
✓ The year is the week times fifty-two — 28 units a week is 1456 a year
✓ The standing charge is counted separately from the usage — £364 of electricity plus £219 of standing charge — the second is there whether you use it or not

What this generator does

Multiplies watts by hours and divides by a thousand for units, prices them at your tariff, adds the standing charge as its own line, and divides a replacement's price by the annual saving.

How to use this tool

Pick a typical appliance to start from, or type the watts off the plate.
Say how long it runs and how often.
Put in your tariff and standing charge from the bill.
Add a replacement's wattage and price to see the payback.

Understanding the controls

Start from a typical appliance: A short list of common appliances with typical wattages and usage, as a starting point. The figures on your own plate beat any of them.
Power in watts: From the plate on the appliance. Motors and heaters draw their rated power; electronics rarely draw their maximum.
Hours a day it runs: Time the appliance is actually drawing power, not the time it is plugged in. A fridge cycles, so it runs far less than the day is long.
Days a week: How often. A tumble dryer run three times a week costs less than half one run every day.
Tariff, pence a unit: Pence per kilowatt-hour, off the bill. This is the number the whole calculation hangs on, so take it from a real bill rather than memory.
Standing charge, pence a day: The daily charge for being connected. It is reported as its own line, because it is not caused by the appliance and cannot be saved by using it less.
Replacement's power in watts: The wattage of something more efficient, to compare against. Zero leaves the payback calculation out.
What the replacement costs: The purchase price, divided by the annual saving to give the payback period.

Common use cases

Finding out what the tumble dryer really costs to run
Comparing a hot wash against a cold one in money
Deciding whether a more efficient appliance is worth buying now
Working out what leaving something on standby costs over a year
Explaining a bill to somebody who thinks the standing charge is usage

How this generator works

Watts times hours divided by a thousand gives kilowatt-hours; units times the tariff gives pence; pence divided by a hundred gives pounds. Each step is reported so you can see where a figure came from. Everything is kept at full precision and rounded only where it is shown — rounding the weekly figure to a penny and multiplying by fifty-two puts the annual figure out by enough to fail the check, which is how that mistake was found. The check runs the chain backwards: the cost divided by the tariff must give back the units, and the units divided by the hours must give back the watts.

Randomness and fairness

Nothing is random. The same appliance and tariff always give the same cost.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

Rated wattage is a maximum for many appliances; a washing machine draws that only while heating.
Appliances that cycle, such as fridges, run for a fraction of the time they are switched on — put in the running time, not the plugged-in time.
Tariffs with different day and night rates need working out separately for each.
This is electricity only, and takes no account of gas, water or detergent.

Privacy and your data

Your tariff and usage are used only for the arithmetic on this page, in your browser, and are never uploaded or stored.