EV Charge Time — Method
Charging time is simply the energy you need to add divided by the rate you can add it. Energy = battery capacity × the state-of-charge change; power is the charger output reduced by charging efficiency (≈90% for AC). So time = kWh added ÷ (charger kW × efficiency). The estimate is linear, which is accurate for AC charging and for DC up to about 80%; beyond that the battery management system tapers the current to protect the cells, so the last 20% takes proportionally longer.
Frequently Asked Questions
Time = battery kWh x (target% - start%) divided by (charger kW x efficiency). A 60 kWh car from 20 to 80% on a 7 kW charger at 90% efficiency takes about 5.7 hours.
The battery management system tapers the current above about 80% to limit heat and protect the cells, so the last portion charges much more slowly. Most rapid-charge time figures are quoted to 80%.
No - AC charging is limited by the car onboard charger. A 22 kW wallbox only delivers 7 kW if the car onboard charger is 7 kW. DC rapid chargers bypass the onboard charger.
About 90% for AC charging (losses in the onboard charger and cabling); DC rapid charging is typically a bit higher at the battery but varies with temperature and state of charge.
Cost = energy added (kWh) x tariff. Range added ≈ energy added ÷ the car consumption (kWh per 100 km or per mile).
EV Charging Time Explained
How long an electric car takes to charge comes down to two numbers: how much energy you are adding, and how fast you can add it. The first is set by the battery size and the change in state of charge; the second by the charger power and efficiency.
The estimate
time = kWh added ÷ (charger kW × efficiency). This is accurate for AC charging across the whole range and for DC up to ~80%.
The taper
Above ~80% the battery management system reduces current to protect the cells, so the final stretch is slower — that is why rapid-charge claims stop at 80%. The AC rate is also capped by the car onboard charger, not just the wallbox. To size the home circuit, use the EV charging circuit calculator.
Related: EV Charging Circuit, Cable Sizing.