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MasterMath

EV Charging Cost Calculator

What it costs and how long it takes to charge an electric car, counting the losses in charging, which are not negligible.

Currency and number format for

Cost of the charge

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Cost of the charge—
Energy into the battery—
Energy billed—
Charging time—
Range added—
Cost per 100 km—

How this was worked out

    The formula

    cost = kWh into the battery ÷ efficiency × price per kWh

    Where it comes from

    Not everything billed reaches the battery: on alternating current around 10 % is lost in the on-board charger and as heat. That is why the kilowatt hours the meter charges for are always more than the ones that go in.

    How to work it out by hand

    1. Work out the kWh needed from the percentage to charge
    2. Divide by the charging efficiency, around 90 %
    3. Multiply by the price of a kilowatt hour
    4. Divide the billed kWh by the charger's power for the time

    What is worth knowing

    Charging from 20 % to 80 % is what to do day to day: below 20 % and above 80 % the battery degrades faster, and rapid charging slows a great deal past 80 % to protect the cells. A full charge to 100 % is worth saving for long trips.

    Frequently asked questions

    What does it cost to charge an electric car?

    From 20 to 80 % on a 60 kWh battery is about 40 kWh billed: at 0.15 per kWh, around 6.

    Why is more billed than goes into the battery?

    Because charging is 85-90 % efficient: the rest is lost in the charger and as heat.

    How long does charging take?

    On a 7.4 kW home charger, about five and a half hours to go from 20 to 80 %. On a rapid charger, under half an hour.

    Should I always charge to 100 %?

    No. Day to day, 20 % to 80 % is what is recommended, because the extremes degrade the battery faster.