What charging an EV at home actually costs

Charging at home is normally much cheaper than charging in public, and the gap is wide enough to change what a car costs to run. The calculation takes two numbers and one division, and it is worth doing for each tariff you might be on.

Everything below uses your figures, not averages, because the spread between households is larger than the spread between cars. A worked example runs alongside so you can check your own arithmetic.

The calculation

Pence per mile = unit rate in pence per kilowatt hour, divided by miles per kilowatt hour.

That is it. Two inputs:

Your car’s real efficiency, in miles per kilowatt hour. The trip computer gives a running average. Use the lifetime figure rather than a good recent journey, and expect winter to be worse: cold batteries and cabin heating both take their share.

The unit rate you would pay, in pence per kilowatt hour, at the time you would actually charge.

Do the division three times, with a car returning 3.5 miles per kilowatt hour as the example:

• Standard rate: the capped 26.11p per kilowatt hour gives about 7.5p per mile.
• EV tariff off peak: Intelligent Octopus Go’s 8p window gives about 2.3p per mile.
• Public rapid: even a discounted public rate, such as InstaVolt’s 55p off peak app pricing, gives about 15.7p per mile, and standard daytime rapid rates run substantially higher still.

Across 10,000 miles a year, roughly 2,860 kilowatt hours into the battery, those rates are about £230, £750 and £1,570 respectively. The tariff choice, one form and no hardware, is worth around £500 a year against standard rate charging. That is the whole argument in three divisions.

Do not forget charging losses

Not everything drawn from the wall reaches the battery. Some is lost in the charger, the car’s onboard conversion and battery thermal management.

The loss is modest but real, commonly around a tenth for home AC charging, and it is larger in cold weather when the car is conditioning the battery. If you want to be precise, compare the units your home charger reports against the energy the car reports receiving, and divide your costs by the charger’s figure, since that is what you pay for. If you want to be quick, treat your effective cost as slightly higher than the raw division suggests.

Where the tariff dominates

The charger you buy makes very little difference to running cost. The tariff makes an enormous one, as the £500 gap above shows.

Electric vehicle tariffs typically offer a cheap window overnight in exchange for a standard or sometimes higher rate the rest of the day. Whether that suits you turns on three things:

How much you drive. The saving scales with units consumed. High mileage makes the cheap window valuable; very low mileage may not cover any penalty on your daytime rate.

Whether you can shift other loads. Dishwasher, washing machine and immersion heater on timers all move consumption into the cheap window and add to the benefit, and a grid charging battery can move most of the rest.

What the daytime rate becomes. This applies to all your other electricity, which for most households is a larger volume than the car uses. Multiply any daytime premium by your full non-car consumption before celebrating the overnight rate.

That last point is why an electric vehicle tariff can leave a low mileage household worse off. Work it out rather than assuming: annual car units at the cheap rate, plus everything else at the tariff’s daytime rate, against your whole consumption at your current flat rate.

Comparing with public charging

Run the same division with a public rapid rate and the difference is usually stark, as the example shows: the discounted public rate is seven times the EV tariff’s overnight rate. Rapid charging carries the cost of the infrastructure, the grid connection and the operator’s margin, and it is priced accordingly.

The practical conclusion for most drivers: home charging for routine use, public rapid charging for journeys that need it, and accept that occasional rapid charges will lift your average cost per mile above the home figure. A driver doing nine tenths of their charging at 8p and a tenth at public rates still averages under 4p a mile in the example car.

If you cannot charge at home at all, the arithmetic is different enough that it belongs in the decision about whether to buy the car.

What about the charger itself

A home charger is a capital cost that does not recur, and it should be judged separately from running cost.

Points worth checking:

• Whether your supply can support it without work, which an installer will assess.
• Whether it can be scheduled, so it charges in the cheap window automatically.
• Whether it can modulate to follow surplus solar generation, if you have or plan panels.
• Whether it needs the car plugged in and awake to start a scheduled session.

The scheduling capability is the one that determines whether you actually realise the tariff saving, or merely have access to it in principle. A charger that cannot hit a 02:00 window reliably converts the £500 tariff gap back into theory.

Then model it against solar

If you have panels or are considering them, the car changes the picture, mostly for the better, because more consumption means more opportunity to use your own generation instead of exporting it at a fraction of its value. The condition is timing, whether the car is home in daylight, which is a separate question worth its own treatment.

Take your annual mileage, your car’s efficiency and your candidate tariffs, work out the annual figure for each, and if solar is in the picture, put the whole household through the calculator with the EV option on. That comparison is specific to you and it takes ten minutes, which per pound of annual difference is the best paid ten minutes in motoring.