At the current price cap rate of 26.11p per kWh, a typical microwave costs about 1.9p per use, which is £13.69 a year on the usage below.
Where that number comes from
Across the range of powers for this appliance class, one use costs between 1.5p and 2.5p. Your own figure is on the rating plate, usually on the back or inside the door, and it is the only one that is true for you.
The cheapest way to reheat anything. The number on the front is usually the cooking power, not the power drawn, which is higher.
What does it cost to run?
Change any of these. The rate is the current price cap average, but yours is on your bill and is the one that matters.
Every other appliance
See the full table at today's rate, or what the price cap is doing next.
Energy figures are worked from the Ofgem price cap on the date shown and from typical power for the appliance class, not from a named model. Your own rate and your own rating plate are the ones that count. Full disclaimer.