How the time is calculated
Energy added to the battery = usable capacity x the change in charge. Energy drawn from the charger is higher because some is lost as heat: divide by the efficiency, which is around 90 per cent on AC.
Charging time = energy drawn divided by charger power. A 60 kWh battery going from 20 to 80 per cent needs 36 kWh, which is 40 kWh from the supply, and takes 48 minutes on a 50 kW charger.
Worked example
A 60 kWh usable battery charged from 20 to 80 per cent gains 36 kWh. At 90 per cent efficiency the charger supplies 40 kWh, and at 50 kW that is 0.8 hours, or 48 minutes.
At a typical 6 km per kWh the added energy is about 216 km of range. These figures are illustrative.
Why the real time is often longer
DC charging tapers. A car may accept 150 kW at low charge and far less above 80 per cent, so the last 20 per cent can take as long as the first 50. The rated charger power is a maximum, not a constant.
Cold weather, a hot battery, sharing a paired charger and the car's own limit all reduce the rate. On AC, the onboard charger is usually the limit: a 7 kW wall box cannot deliver 11 kW to a car that only accepts 7.
Limits of this calculator
It assumes a constant power for the whole session and a single efficiency figure. It does not model the taper, temperature, preconditioning or charger sharing.
For a fuel comparison, use the MPG calculator.
To compare running costs with a petrol or diesel car, use the UK MPG calculator.
Inputs for the EV charging time calculator
Usable battery capacity
The usable figure from the specification, not the larger gross capacity.
Starting charge
State of charge when you plug in, as shown on the car or the charger.
Target charge
The level you want to reach. Above 80 per cent DC charging slows sharply.
Charger power
Rated output of the charger in kW, not the maximum the car can accept.
Charging efficiency
Share of the drawn energy that reaches the battery. Around 90 per cent is typical on AC.
CALCULATOR QUESTIONS
UK EV charging time calculator questions
Why is the time longer than energy divided by power?
Charging losses mean the supply delivers more than the battery stores, and DC charging tapers as the battery fills.
Should I use gross or usable capacity?
Usable. The buffer at the top and bottom is not charged or discharged, so it would overstate the energy needed.
Does a 150 kW charger always deliver 150 kW?
No. The car, the battery temperature and the state of charge all limit it, and paired chargers share their output.
Is charging to 100 per cent bad?
Many manufacturers recommend a lower daily limit for battery life. This calculator does not advise on that; it only estimates time.