How do you calculate EV charging time?
If you know the battery size in kWh, the charging power and the current state of charge, you can work out the time in your head. The formula is simple, but there is a catch with DC charging.
By: Şarj Rehberim · Updated: · 5 min read
The basic formula
Charging time is the energy that has to go into the battery divided by the charging power. Taking the percentage gap into account:
Time (hours) = Battery (kWh) × (Target % − Current %) ÷ 100 ÷ Power (kW)
An example: a car with a 60 kWh battery goes from 20% to 80%. The gap is 60 points, so 36 kWh of energy is needed. From an 11 kW AC socket that is 36 ÷ 11 ≈ 3.3 hours.
Add the losses
That calculation is theoretical. In practice some energy is lost as heat while charging, and the car's cooling system uses energy too. Expect roughly 10% loss on AC and 5–8% on DC.
In the example above, 3.6–3.7 hours is a more realistic expectation than 3.3.
The real limit: the car itself
The station's power and the power your car can accept are not the same thing. Plug a car with an 11 kW on-board charger into a 22 kW AC socket and you still get 11 kW. Use the smaller number in your calculation.
The same applies to DC: connect a car that accepts at most 100 kW to a 180 kW station and the result is 100 kW.
The 80% rule for DC charging
On DC fast charging the power does not stay constant. As the battery fills, the car gradually lowers the current — this is called the charging curve. The highest speeds are usually seen between 20% and 50%; after 80% it slows down markedly.
That is why on a long trip, charging to 80% and moving on is usually faster than waiting for 100%. The last 20% can take as long as the first 60%.
Roughly how long?
DC times in the table are approximate because of the charging curve; they get longer in cold weather.
| Power | Type | 60 kWh battery, 20% → 80% |
|---|---|---|
| 3.7 kW | AC — household socket level | about 10 hours |
| 7.4 kW | AC — home wallbox | about 5 hours |
| 11 kW | AC — three-phase | about 3.5 hours |
| 22 kW | AC — high-power three-phase | about 1.8 hours |
| 50 kW | DC | about 45 minutes |
| 150 kW | DC fast | about 25 minutes |
Frequently asked questions
- Does charging to 100% damage the battery?
- Charging to 100% every day and leaving it there wears a lithium battery. For daily use 20–80% is recommended; before a long trip, charging to 100% is fine.
- Can I charge from a normal 16 A socket at home?
- Technically yes, but it is not suitable for regular use. A normal socket is not designed to carry high current for hours and there is a risk of overheating. You need a wall-mounted charging unit.
- Why does it charge more slowly in the cold?
- When the battery is cold, the car limits the current it accepts to protect the cells. In some cars, entering a charging station into the navigation pre-heats the battery, which largely solves this.