The method
Divide the miles by your car's efficiency in miles per kilowatt-hour to get the energy used. Add a little for charging losses, because some electricity is lost as heat while charging. Multiply by the price per kilowatt-hour. For 1,000 miles at 3.5 miles per kilowatt-hour with 10% losses, the car draws about 314 kilowatt-hours; at 7.5p per kilowatt-hour that is about £23.57.
Where you charge matters most
Home charging on an overnight tariff is usually far cheaper per kilowatt-hour than public rapid chargers. Enter the price you actually pay: your tariff, or the price shown on the charger.
Efficiency changes with the weather
Electric cars use more energy in cold weather and at motorway speeds. Your car's trip computer shows your real miles per kilowatt-hour, which gives a better answer than the brochure figure.
Comparing with petrol
The charging cost calculator shows the same miles in a petrol car so you can see the difference. It does not include other costs such as servicing, tyres, insurance or the price of the car.