One of the real attractions of an electric car is how cheap it can be to run, but only if you charge it sensibly. Home charging on the right tariff is about the lowest-cost way there is to fuel a car; home charging on the wrong tariff, or relying on public rapid chargers, can erode much of that advantage. The difference comes down to the price you pay per kilowatt-hour.
The simple sum
Charging an EV is just buying electricity, so the cost is the energy you put in multiplied by your price per unit. An electric car's efficiency is usually quoted in miles per kilowatt-hour, and a typical car manages somewhere around three to four miles from each kWh, depending on the car, the weather and how you drive. So to drive a given number of miles you divide by that figure to get the kWh needed, then multiply by your electricity price. The running cost calculator handles the arithmetic if you treat the charger as the appliance and your weekly mileage as the usage.
Why the tariff is everything
Here is the lever that dwarfs all others. Charge from a standard day-rate tariff and an EV is reasonably cheap to run. Charge overnight on a dedicated off-peak EV tariff, where the unit price in the small hours can be a fraction of the daytime rate, and the cost per mile drops to a level petrol cannot approach. The same energy, bought at the cheap overnight window instead of the peak, can cost a third or less. This is why a smart meter and a time-of-use tariff are close to essential for getting the most from an electric car at home.
A worked example
Take a car doing three and a half miles per kWh and a week of two hundred miles. That is roughly fifty-seven kWh of charging. At an example peak rate of 30p per kWh that week costs around seventeen pounds; at an example off-peak rate of 8p per kWh it costs under five. Those numbers are illustrative and your own rates will differ, but the shape is the point: the tariff, not the car, decides whether your electric motoring is merely cheaper than petrol or dramatically so. Shifting charging into the off-peak window is the single biggest thing you control.
Home charger versus the three-pin plug
You can charge from an ordinary three-pin socket, but it is slow, delivering only a few miles of range per hour, and a domestic socket is not really designed for hours of heavy continuous draw. A dedicated home wall charger is faster, safer for sustained charging, and crucially can be scheduled to run only during your cheap off-peak window automatically. For anyone charging regularly at home, a proper charger usually earns its keep through convenience and by making off-peak charging effortless rather than something you have to remember to start and stop.
Home versus public charging
Charging at home off-peak is the cheapest option by a wide margin. Public charging, especially rapid and ultra-rapid chargers, is far more expensive per unit, sometimes several times the home off-peak rate, because you are paying for speed, convenience and the cost of the infrastructure. That is fine as an occasional top-up on a long journey, but a driver who relies on public rapid charging for everyday miles loses much of the running-cost advantage an EV should give. The model that saves the most is simple: do the bulk of your charging slowly and cheaply at home overnight, and use public chargers only to extend range on longer trips.
How it compares with petrol
Even on a standard tariff, the cost per mile of an electric car is generally below that of an equivalent petrol or diesel car, and on an off-peak home tariff it is far below. The fuel saving is one of the clearest running-cost advantages of going electric, though it should be weighed against the whole picture of buying and owning the car rather than treated alone. If you are still running a combustion car, the habits on the hypermiling and fuel and driving pages remain the way to trim its thirst; if you have gone electric, the equivalent skill is simply charging at the right time.