Our calculator takes your annual mileage figure and then applies it as follows (assume you drive 7,000 miles a year):
For electric cars: to cover 7,000 miles a year, in an EV with average efficiency of 3.5 miles per kWh, you need 2,000 units (kWh) of electricity. The maths is: 7,000 divided by 3.5 = 2,000. Charging at home off-peak at 7.5p per kWh will cost you £150 a year.
For petrol/diesel cars: we assume an average engine efficiency of 39.5 mpg and an average fuel price of £1.7149 per litre. To cover the same 7,000 miles, you need 805.64 litres of fuel which will cost you £1,382 per year.