How long an electric car takes to charge is a simple question with a surprisingly practical answer: it is the energy you need to add, divided by the power the charger can deliver. A plain 120 V household outlet adds only a few miles of range per hour, a 240 V home wall box fills most batteries overnight, and a DC fast charger can add hundreds of miles in half an hour — as long as the car is able to accept that power. This calculator puts the numbers together.
How to use the EV charging time calculator
- Enter the usable battery size in kWh.
- Set the start and end charge levels. For fast charging the usual comparison is 10% to 80%.
- Enter the charger power. You can type it directly in kW, or work it out as volts × amps ÷ 1000 (see the table below).
- Optionally enter the car’s own maximum charge rate. The calculator then uses whichever is lower — the charger or the car.
The result gives the time in hours (or minutes through the menu), the energy added to the battery and the energy drawn from the supply. To price the session, copy the energy figure into the EV charging cost calculator.
Charging time formula
Energy from the supply = energy stored ÷ efficiency
Charging power = min(charger kW, car’s maximum kW)
Time (hours) = energy from the supply ÷ charging power
AC charger power (kW) = volts × amps ÷ 1000
Dividing by efficiency adds the energy lost as heat during conversion, so the time you see is the time on the charger, not just the time to fill the battery on paper. A constant-power estimate is accurate for AC charging, where the car draws a steady rate for most of the session. DC fast charging follows a curve — a high rate in the middle of the battery, tapering toward full — so use the 10–80% range and the car’s average rate for DC sessions.
Worked example: overnight at home
A car with a 75 kWh usable battery is plugged in at 20% and unplugged at 80% on a 240 V, 32 A home charger. Efficiency is 90%.
- Charger power: 240 × 32 ÷ 1000 = 7.68 kW.
- Energy stored: 75 × 60 ÷ 100 = 45 kWh.
- Energy from the supply: 45 ÷ 0.90 = 50 kWh.
- Time: 50 ÷ 7.68 = 6.51 hours, about 6 hours 31 minutes.
Charging time by charger type
Power for each row is volts × amps ÷ 1000 for AC chargers, or the nominal rating for DC chargers. The time is for adding the same 45 kWh (20% to 80% of a 75 kWh pack) at 90% efficiency.
| Charger | Power | Time for a 45 kWh top-up (90% efficient) |
|---|---|---|
| Level 1 — 120 V × 12 A | 1.44 kW | 34.7 h |
| Level 2 — 240 V × 32 A | 7.68 kW | 6.5 h |
| Level 2 — 240 V × 48 A | 11.52 kW | 4.3 h |
| DC fast — 50 kW | 50.00 kW | 1.0 h |
| DC fast — 150 kW | 150.00 kW | 20 min |
What limits your real charging time
Three things separate the calculator from a real session. First, the car’s onboard charger: many vehicles accept only 7 to 11 kW on AC, so plugging into a 19 kW public AC station does not make it faster. Second, temperature: a cold battery charges more slowly until it warms up, and many cars precondition the pack on the way to a fast charger. Third, the charge curve: charging power falls steeply above roughly 80%, which is why road-trip planners stop at 80% and move on.
For home charging, remember that continuous electrical loads are limited to 80% of a breaker’s rating under US electrical practice, which is why a 40 A circuit typically supports a 32 A charger. Check your car’s manual and an electrician’s advice before choosing a charger or circuit; this calculator only estimates time and does not replace safe installation guidance.
Sources
Charging levels and efficiency considerations are described by the US Department of Energy and EPA at fueleconomy.gov and afdc.energy.gov. The AC power formula (power = voltage × current) is basic electrical engineering.
Frequently asked questions
How long does it take to charge an electric car at home?
A 75 kWh car adding 45 kWh on a 7.68 kW Level 2 charger (240 V, 32 A) takes about 6.5 hours including losses, so an overnight charge is enough for most daily driving. On a 120 V outlet at 1.44 kW the same top-up takes about 35 hours.
How do I work out charger power in kW?
Multiply volts by amps and divide by 1000. A 240 V circuit at 40 A gives 9.6 kW. Wall boxes are usually limited to 80% of the breaker rating for continuous loads.
Why does fast charging slow down after 80%?
To protect the cells, the car reduces the charge rate as the battery fills. Quoted times for DC fast charging are normally for 10–80%. This calculator uses a constant power, so for DC sessions use the 10–80% range and the car’s average rate.
Does the car limit how fast it charges?
Yes. Many cars cannot accept more than 7–11 kW from an AC charger, and every DC-capable car has a peak DC rate. Enter that limit in the optional box to get a realistic time.
How accurate is the estimate?
It is a straight-line estimate. Cold weather, battery temperature and the taper near full will make real sessions longer, especially on DC fast chargers.