The Two-Pence Illusion: Calculating Your True Home EV Charging Cost per Mile in 2026

The advert versus the meter

A smart tariff advertising 7p per kWh overnight appears to offer motoring at about 2p per mile. The arithmetic is simple: an EV using 3.5 miles per kWh consumes roughly 0.286 kWh per mile, and 0.286 multiplied by 7p is 2p. It is also incomplete.

The meter does not measure energy at the battery. It measures energy drawn from the grid, and some of that is lost in the charger, the cable and the car’s onboard conversion. Not every kilowatt-hour is bought at the off-peak rate. The standing charge arrives whether the car is plugged in or not. The charger itself has a cost. Regional distribution charges vary. The true pence-per-mile figure is therefore a calculation, not a slogan.

Step one: convert pence per kWh to pence per mile correctly

The correct formula is:

Pence per mile = pence per kWh × grid kWh per mile

Grid kWh per mile = 1 ÷ (miles per kWh × charging efficiency)

For a car achieving 3.5 miles per kWh and a charging efficiency of 90%, the grid energy per mile is 1 ÷ (3.5 × 0.9) = 0.317 kWh. At 7.5p per kWh, the energy cost is 2.38p per mile. At a peak rate of 26p per kWh, the same mile costs 8.25p.

That 2.38p figure is the best-case marginal cost of off-peak home charging. It is already higher than the advertised 2p because it includes losses. It still excludes the fixed and semi-fixed costs that make up a real household bill.

Step two: not every home kilowatt-hour is off-peak

Smart tariffs typically offer a fixed overnight window, often four or five hours. A 7 kW home charger running for four hours can deliver around 28 kWh, which is enough for roughly 80 to 90 miles in a 3.5 miles per kWh car. A single commuter doing 30 miles a day will usually fit inside the window. A two-EV household, a driver doing 100-mile days, or a car with a smaller off-peak window will need some peak-rate top-ups.

Take a driver covering 7,500 miles a year, with 85% of charging at home and 15% on public networks. Home mileage is 6,375. At 0.317 kWh per mile, home grid consumption is about 2,024 kWh. If 80% is bought at 7.5p and 20% at 26p, the annual home energy cost is roughly £121 for off-peak energy and £105 for peak energy, or £226 in total. That is 3.56p per home mile before standing charges and equipment.

Step three: standing charges are not free

A smart tariff may carry a standing charge of around 60p per day, or £219 a year. It is tempting to divide that entire sum by the EV’s annual mileage, but that would overstate the EV’s cost because the household would pay a standing charge for its other electricity anyway.

A fairer approach is to count the tariff premium. If the EV-specific smart tariff costs 10p per day more than the household’s previous tariff, the incremental cost is £36.50 a year. Spread over 6,375 home miles, that adds about 0.57p per mile. If the whole standing charge is allocated to the EV, the figure rises to about 3.4p per mile. Both figures are defensible for different purposes: the premium is useful for deciding whether to switch tariff, while the full allocation is useful for a total cost of ownership exercise that treats the EV as the reason for the supply.

Step four: the charger is part of the cost

A professionally installed 7 kW home charger might cost around £1,000 in 2026 before any grant or tax treatment. Assuming a five-year life and no residual value, that is £200 a year. Over 6,375 home miles, it adds about 3.14p per mile. If the installation is £650 after a grant, the figure falls to about 2.04p per mile.

This is where the 2p claim collapses most visibly. The charger is not optional for convenient home charging, and its cost is not included in the electricity tariff. A driver who already has a charger, or who charges mainly at work, will see a lower figure. A driver installing a charger for a low annual mileage will see a higher one.

The true home figure

Adding the illustrative elements together gives:

• Energy, including 20% peak-rate top-ups: 3.56p per mile
• Incremental standing charge: 0.57p per mile
• Charger installation, amortised over five years: 3.14p per mile

That is about 7.27p per mile for home charging. If the driver also pays for 15% public charging at 79p per kWh, the public miles cost about 25.1p per mile on energy alone. Across 7,500 miles, the combined annual cost is roughly £745, or about 9.94p per mile. The exact figure will move with efficiency, tariff, mileage and installation cost, but the direction is clear: home charging is much cheaper than public rapid charging, and much more expensive than the headline 2p suggests.

Regional differences are real

A driver in northern Scotland, London, south Wales and rural East Anglia will not see identical unit rates or standing charges. Distribution charges, local network costs and supplier pricing vary. An off-peak rate of 6.5p in one region and 9p in another changes the energy cost on 1,619 off-peak kWh by around £40 a year, or about 0.6p per mile. A 20p per day difference in standing charge adds another £73 a year, or about 1.1p per mile at this mileage.

Off-peak windows also differ. A four-hour window is not the same as a five-hour window for a high-mileage driver. A tariff that looks cheap per kWh can be less useful if the car cannot absorb enough energy overnight without resorting to peak-rate power.

What the 2p figure is good for

The 2p per mile calculation is not dishonest; it is a marginal energy calculation. It is useful for comparing one off-peak rate with another, or for estimating the saving from shifting a charging session from peak to off-peak. It is not a total cost of ownership figure, and it should not be used to compare an EV with a petrol or diesel car without adjustment.

For that comparison, use the realistic home figure of roughly 7p to 10p per mile, depending on installation and public charging mix. A petrol car doing 45 mpg at £1.35 per litre costs about 13.6p per mile in fuel alone. The EV remains cheaper, but the margin is narrower than the headline tariff implies.

How to calculate your own figure

Start with the car’s real miles per kWh from the trip computer, not the brochure. Add about 10% for charging losses. Split annual home consumption between off-peak and peak using a charging log or the supplier’s app. Add either the tariff premium or the full standing charge, and state which method is being used. Amortise the charger over its expected life. Finally, add public charging at the rate actually paid, not the lowest advertised rate.

The result will be a number that survives scrutiny. It will almost certainly be higher than 2p per mile, and it will be a more honest basis for deciding whether a smart tariff, a home charger or a public charging membership is worth the money.