THE SHORT ANSWER
Multiply the energy taken from the grid by your electricity price. For a useful estimate, include charging losses rather than multiplying the battery percentage alone. The calculator below does this and also estimates your cost per mile.
YOUR FIGURES
Charging cost calculator
Blend cheap home charging with the public charging you expect to use.
How the calculation works
First calculate the usable battery energy being added: battery capacity multiplied by the change in state of charge. A 60 kWh battery charged from 20% to 80% receives about 36 kWh inside the battery.
The wall supplies slightly more energy because charging is not perfectly efficient. Divide the battery energy by the charging efficiency, then multiply the result by your electricity price per kWh.
- Battery energy added = battery size × percentage added.
- Grid energy = battery energy added ÷ charging efficiency.
- Session cost = grid energy × electricity unit rate.
- Driving cost per mile = electricity unit rate ÷ miles per kWh, adjusted for charging losses.
Use the rate that will actually charge the car
If your tariff has a cheap overnight window, use that price only for energy that genuinely fits inside the window. Any remaining charging may fall onto the day rate. Public charger prices normally include VAT and are shown by the operator, but subscriptions or overstay fees can alter the final cost.
Also compare the whole household tariff. A very cheap EV rate can be offset by a higher daytime price if much of your home electricity is used during the day.
Why your bill will not match perfectly
Temperature, battery conditioning, charge speed and the car's electronics all affect losses. The car's displayed battery percentage is also rounded. Treat the result as a planning estimate and compare it with your charger or energy supplier's recorded kWh after a few weeks.
COMMON QUESTIONS
Frequently asked questions
How do I calculate the price of a full EV charge?
Multiply the battery energy added by your electricity rate, then allow for charging losses. Charging from 0% to 100% is rarely the normal pattern, so using your usual start and end percentages is more useful.
Is home charging always cheaper than public charging?
Home charging is normally cheaper, especially on an off-peak tariff, but compare your actual tariff with the price shown by the public charging operator.
Why does the charger supply more kWh than the battery receives?
Some energy is used by power conversion, battery temperature control and vehicle systems during charging. That is why the calculator includes an efficiency allowance.
SOURCES & FURTHER READING
Check the current guidance
Rules, grants, tariffs and prices can change. Follow the linked source before making a financial or installation decision.