EV Charging Cost Calculator

How it works

Energy added to the battery is capacity × (target % − start %) ÷ 100. Chargers and the battery are not 100% efficient: some energy is lost as heat. Grid energy is battery energy divided by efficiency as a decimal, so 36 kWh added at 90% efficiency draws 40 kWh from the socket. The default 90% is a planning assumption for AC charging, not a measurement of your car. DC fast charging, cold weather and high state of charge can all change the real figure. This is not a utility bill.

Formula

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

Worked examples

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

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.

Related tools

• EV Charging Time
• Electricity Cost
• kWh Cost