Charging time depends on the energy you need, not only the battery’s full size. Divide that energy by usable charging power after losses. Then allow for the car reducing power because of temperature, battery level or a schedule.
Calculate the energy you need
Multiply usable battery capacity by the change in state of charge. A 60 kWh usable battery moving from 20% to 80% needs 36 kWh in the battery.
The calculation is 60 kWh × (0.80 − 0.20) = 36 kWh. Do not use gross battery capacity when the maker provides usable capacity.
For daily planning, you can start from driving instead. A car using 18 kWh per 100 km needs about 9 kWh in the battery after a 50 km trip. Weather and speed can change that consumption.
Find the lowest power limit
The supply, charging equipment, cable and onboard charger each have a maximum. The lowest active maximum sets the power ceiling. Actual power may be lower.
An 11 kW car does not take 22 kW AC from a larger wallbox. A three-phase wallbox may provide much less to a single-phase car. A load-management system can lower power when the home needs electricity elsewhere.
Use the power the car actually reports when you have session data. Use rated power only for a first estimate.
Include charging efficiency correctly
Some wall energy becomes heat or runs pumps, electronics and battery conditioning. If you use an efficiency of 90%, multiply input power by 0.90 before dividing.
For 36 kWh at 11 kW, the estimate is 36 ÷ (11 × 0.90) = about 3 hours 38 minutes. At 2.3 kW, it is 36 ÷ (2.3 × 0.90) = about 17 hours 24 minutes.
Efficiency is not a universal constant. It varies with vehicle, power, temperature and battery controls. A measured session gives a better value for your car.
Do not multiply time by efficiency
Losses make charging longer. Use time = energy ÷ (power × efficiency). Using energy ÷ power × efficiency would incorrectly make a lossy session shorter.
Compare common home powers
The table estimates time to add 36 kWh to the battery. It assumes 90% efficiency and steady input power.
| Input power | Estimated time |
|---|---|
| 2.3 kW | 17 h 24 min |
| 3.7 kW | 10 h 49 min |
| 7.4 kW | 5 h 24 min |
| 11 kW | 3 h 38 min |
| 22 kW | 1 h 49 min |
The 22 kW row applies only to a car that accepts 22 kW AC. A session does not stay at a theoretical maximum when the car or load manager reduces it.
Why can the real session take longer?
The vehicle controls the battery. It may reduce power when the battery is cold, hot or near a charge limit. AC near-full behavior is model-dependent, so do not apply one taper rule to every EV.
Cabin or battery preconditioning can also use incoming energy. Scheduled charging may pause until a chosen time. A wallbox with load management may change power throughout the session.
The displayed charge level is an estimate from the battery-management system. Small differences between the calculated and displayed result are normal.
Plan around departure, not zero to full
Most home sessions replace part of the battery. Record your normal arrival level, desired departure level and parking time. This gives a useful target without buying power you rarely need.
If the calculation finishes before departure with a margin, the charger is fast enough. If not, consider starting earlier, charging more often or increasing power after an electrical assessment.
Frequently asked questions
What is the formula for EV charging time?
Estimated time equals energy needed divided by the product of input power and estimated efficiency: energy ÷ (power × efficiency). Use the lowest power ceiling in the charging chain.
How long does 11 kW charging take?
Adding 54 kWh to the battery takes about 5 hours 27 minutes at 11 kW with 90% efficiency. The car may reduce power, which makes the real session longer.
Does charging slow near 100%?
It can. Vehicle battery controls may reduce power as the battery fills. The behavior and timing differ by model, battery temperature and charging method.
Why is winter charging slower?
A cold battery may accept less power, and the car may use energy to warm it. Preconditioning while connected can help on vehicles that support the feature.
