MultiConvers

EV Charging Cost Calculator

Estimate what one charge session costs from usable pack size, start and target state of charge, the electricity price, and charging efficiency. Energy added to the battery is not the same as energy pulled from the grid — the default 90% efficiency is why.

Updated

How to use

  1. Enter battery capacity in kWh (the usable figure you plan with, if you have it).
  2. Set start % and target %. Target must be at or above start; 20% to 80% on 60 kWh is 36 kWh added.
  3. Enter price per kWh and efficiency (default 90). Grid energy is battery energy ÷ efficiency.
  4. Read energy added, grid kWh and cost. For how long the session takes, use EV Charging Time — this page has no charger kW.

How it works

Energy added is capacity × (target − start) / 100. A 60 kWh pack from 20% to 80% needs 36 kWh into the cells. The meter on the wall sees more, because inverters, cables and the pack itself discard heat. Grid energy is 36 ÷ 0.90 = 40 kWh at the default 90%. At 0.20 per kWh that session is 8.00. Set efficiency to 100% only if you want a lossless lower bound; real AC home charging is rarely that clean.

Ninety percent is a planning guess for typical AC, not a measurement of your car, cable or weather. Cold packs, DC fast charge, and the last stretch toward 100% usually waste more. If you have a wall-meter versus dash-kWh pair from last week, back out efficiency and type that instead of 90.

The page does not know charger power, idle fees, parking, or public-network connection charges. It will not split a time-of-use tariff. It rejects a target below the start, percents outside 0–100, non-positive capacity, or efficiency that is 0 or above 100. Price may be zero (a free overnight rate) but not negative.

kWh Cost is the last multiply alone if you already know grid kilowatt-hours. Electricity Cost is watts × hours. EV Charging Time divides the same battery energy by charger kW and ignores losses. Use that for a clock estimate, this page for a bill estimate.

This is not a utility invoice and not the car’s trip computer. Standing charges are omitted.

Formula

Energy added (kWh) = capacity × (target % − start %) ÷ 100
Grid energy (kWh) = energy added ÷ (efficiency % ÷ 100)
Cost = grid energy × price per kWh

Worked examples

  • 20% to 80% on a 60 kWh pack

    60 kWh, 20% → 80%, 0.20/kWh, 90% efficiency → 36 kWh added, 40 kWh from the grid, cost 8.00

  • Empty to full, lossless

    50 kWh, 0% → 100%, 0.30/kWh, 100% efficiency → 50 kWh added, 50 kWh from the grid, cost 15.00

Useful notes

  • Default efficiency is 90% (about 10% lost). Set 100% if you want an idealised, lossless figure.
  • Start and target are battery percentages, not charger power. Time to charge is a different calculation.
  • No idle fees, parking or time-of-use bands — only grid kWh × the price you type.

FAQ

Why is grid energy higher than battery energy?

Charging losses. If efficiency is 90%, the car stores 90% of what the meter records. The extra 10% is mainly heat in the charger and battery.

What efficiency should I use?

90% is a reasonable AC home-charging starting point. Use a lower number in the cold or on a fast charger if you have data; use 100% only for a theoretical minimum.

Does this include public-charger idle fees or parking?

No. It only multiplies estimated grid kilowatt-hours by the energy price you enter.

Why can’t target be lower than start?

This page models adding energy, not discharging. A lower target would be a drive, not a charge session.

Is battery capacity the brochure number or usable kWh?

Use the figure you want the math on. Usable kWh matches what the car will actually accept between the percents you type.

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