Running cost calculator
Pick the device, or type its wattage, and set the hours you actually use it. Three numbers decide the answer, and none of them leave your browser.
What each field means. Power draw is the figure on the label, in watts, while the device is working. Hours of use is how long you run it on a day you run it at all. Days a week is how often that happens. Price is your all-in rate from the bill, in cents per kilowatt hour. Duty is the share of the time the device actually draws power once it is switched on. The monthly bill is optional and only used for the share line.
Every appliance on a bill is the same arithmetic: power x hours x price. This page does that arithmetic for one device at a time and shows the monthly and yearly figure, because the monthly figure is the one that changes a decision.
Almost nothing draws its label wattage all the time. Heaters cycle on a thermostat, fridges cycle on a compressor, ovens hold temperature. The duty cycle field is what keeps the answer honest, and it is the field most calculators leave out.
Nothing is sent anywhere. The calculation runs in your browser.