EV charging costs at home: work out your mileage, losses and tariff mix

The number on the tariff is only the beginning

To budget for charging, you need annual mileage, the car’s driving efficiency and the price paid for energy in each place you charge. Then allow for charging losses. A dashboard showing miles per kWh normally describes driving energy; it does not mean every unit recorded by the electricity meter reaches the battery.

Keep the units clear. kW is power: how quickly energy can flow. kWh is energy: the amount you buy or store. A 7 kW charge point does not add £7 to the bill, and a large battery does not automatically make every mile expensive.

A worked annual charging budget

Take an example of 8,000 miles a year at 3.5 miles per kWh, with 90% charging efficiency. Driving uses about 2,286 kWh. Buying enough electricity to supply that energy requires 2,286 ÷ 0.9 = about 2,540 kWh. The roughly 254 kWh difference is charging losses.

Those are reference points, not a claim that all your charging can happen overnight. Now assume 80% of charging energy is bought at home, and 80% of that home energy is bought off-peak. The remaining 20% of all charging happens in public. At the same example rates, the budget becomes approximately £602 a year, £50 a month or 7.5p a mile. The calculator shows the three contributions separately.

Check what fits into the cheaper hours

A charger’s badge is not a guarantee of sustained power. Energy Saving Trust explains that the car’s charging capability can limit the charge point. The supply, load management and other household demand can also affect the available power.

Ask what happens when the car charges at the same time as a home battery or heat pump. Compare the hours available and the energy needed before the next journey. If some charging spills outside the cheap period, reduce the off-peak share in the calculation. Do not use the overnight price for all miles simply because the tariff advertises it.

A cheaper car bill can still mean a dearer home bill

Compare the proposed daytime rate and standing charge as well as the charging rate. For example, an extra 3p on 3,000 kWh of other household imports adds £90 a year. An extra 10p daily standing charge adds £36.50. Those two fictional changes would use up £126.50 of any vehicle saving.

Check eligibility for the exact vehicle, charger and meter before switching. Read our time-of-use tariff guide and use the whole electricity bill comparison if you also export solar. For time-varying tariffs, use rates weighted by when your electricity is actually imported and exported.

Take a useful brief to the installer

• Your typical daily miles and the longest regular journey.
• Where the car parks, the cable route and who controls the parking space.
• The car’s AC charging limit and the proposed charger model.
• Whether solar, a home battery or another large load shares the supply.
• The complete installed price, including any required electrical work.
• The warranty, app requirements and arrangements if smart charging stops working.

For a specific hardware example, read our Project EV APEX 7.3kW buying guide. It explains the model and installation questions without assuming that one charger suits every home.