What decides an EV's running cost
Two numbers do most of the work: how efficient the car is, measured in miles per kWh, and how much you pay for electricity. A typical EV manages about 3.5 miles per kWh. At the standard home rate of around 25p per kWh, that's roughly 7p a mile. Switch to a cheap overnight EV tariff near 7p per kWh and it drops to about 2p a mile.
How petrol compares
A petrol car doing 45 mpg, with petrol around 169p a litre, costs about 17p a mile. So over 10,000 miles a year, home charging an EV might cost around £700 against roughly £1,700 for petrol, saving about £1,000 a year on fuel alone.
Where the gap narrows
Public rapid chargers are much dearer than home charging, often 65p to 90p per kWh, which works out around 20p to 25p a mile, similar to petrol. If you can't charge at home, the savings shrink a lot. Cold weather, motorway speeds and a heavy right foot all lower miles per kWh too.
The bigger picture
This tool covers fuel only. Electric cars also tend to be cheaper to service, with fewer moving parts, and many pay low or no vehicle tax, though that is changing. Against that, they can cost more to buy. If you're getting one through work, pair this with the EV salary sacrifice calculator to see the full monthly picture.