EV Charging Time Calculator

Estimate How Long It Takes to Charge Your Electric Car

EV Charging Time Formula

Formula

\[ E = \frac{C \cdot (SoC_2 - SoC_1)}{\eta} \qquad t = \frac{E}{P} \]

Where:

$C$ — usable battery capacity (kWh)
$SoC_1$ — current state of charge (%)
$SoC_2$ — target state of charge (%)
$\eta$ — charging efficiency (%), the share of grid energy that actually reaches the battery
$E$ — energy drawn from the grid (kWh)
$P$ — charger output power (kW)
$t$ — charging time (hours)

The first equation converts the state-of-charge gap into energy that must come from the grid, with losses included. The second divides that energy by the charger's power to give the time, assuming the charger delivers constant power throughout the session.

EV Charging Time – Calculation Example

Example: an electric car with a 60 kWh battery is at 20% charge and you want to reach 80%. You plug into a 7.4 kW wall box, and charging runs at 90% efficiency.

\[ E = \frac{60 \cdot (80 - 20)}{90} = \frac{60 \cdot 60}{90} = 40 \ \text{kWh} \]

\[ t = \frac{40}{7.4} \approx 5.41 \ \text{h} \]

Result: you need to draw 40 kWh from the grid (36 kWh of which is stored in the battery), and the charge takes about 5.41 hours, or 5 hours 24 minutes.

How to Use the Calculator

Enter your Battery Capacity in kWh (or Wh) — use the usable capacity figure from your car's manual or specification sheet.
Set the Current Charge to the state of charge shown on your dashboard when you plug in.
Set the Target Charge to the state of charge you want to reach.
Enter the Charger Power in kW (or W) — for AC charging, note that the car's on-board charger may limit the actual rate to 7.4, 11 or 22 kW even on a stronger connection.
Adjust the Charging Efficiency if you know a better figure; the default 90% is typical for AC charging at 85–95%.
Read the Energy to Add, the Charging Time in hours, and the same time expressed in hours and minutes.

What Is EV Charging Time and Why It Matters

Charging time is how long a car needs to raise its battery from one state of charge to another at a given charging rate. It depends on three things: how much energy the battery still needs, how fast the charger can deliver it, and how much of that energy is lost along the way as heat in the cables, the charger electronics and the car's on-board charging hardware.

The formula assumes constant power, which describes slow and moderately fast AC charging (home sockets, wall boxes and many public AC points) very well. A 3.7 kW domestic socket adds roughly 15–20 km of range per hour, a 7.4 kW wall box about twice that, and an 11 kW three-phase connection roughly 50–60 km per hour — enough for an overnight top-up in most cases.

The result is best read as a close estimate, not an exact schedule. Real charging sessions can run a few minutes faster or slower depending on battery temperature, cable quality, grid voltage and how much of the car's systems consume power while charging. If you are planning a trip, add a small buffer of 10–20% to the estimate.

Knowing the charging time also helps you estimate the cost of a session: multiply the Energy to Add by your electricity price per kWh. If several drivers share a home charging point, our Bill Split calculator can help divide the electricity bill fairly.

Charger Power Reference

To add 40 kWh from the grid (as in the example above) at 100% utilization, the constant-power model gives:

Charger type	Power	Approx. time for 40 kWh
Domestic socket (AC)	2.3–3.7 kW	11–17 h
Wall box, single-phase (AC)	7.4 kW	5.4 h
Wall box, three-phase (AC)	11 kW	3.6 h
Public AC point	22 kW	1.8 h
DC fast charger	50 kW	48 min
DC fast charger	150 kW	16 min

Note that not every car supports 11 or 22 kW AC charging, and three-phase wall boxes require a three-phase supply at home.

Assumptions and Limitations

Constant power model. The calculator assumes the charger delivers its rated power for the whole session. In reality, DC fast chargers slow down considerably above roughly 80% state of charge to protect the battery, so real 20–80% sessions at high power often take longer than this estimate, and 80–100% sessions much longer.
On-board charger limit (AC). On AC, the car's on-board charger converts grid power to battery power, so the effective rate is the lower of the charger's output and the car's maximum AC input. A 22 kW station can only charge a car with an 11 kW on-board charger at 11 kW.
Efficiency. The default 90% suits typical AC charging. Very low-power charging (e.g. a 2.3 kW domestic socket) tends to be less efficient because fixed overheads consume a larger share of the power, while DC fast charging is often around 90–95%.
Temperature and tapering. Cold batteries charge more slowly, especially below 0 °C, and some cars deliberately limit charging power when the battery is very hot or very cold.
Usable capacity. Enter the usable capacity, not the gross figure quoted in some brochures; they can differ by a few kWh. If in doubt, use the gross value and treat the result as a slight overestimate.

For home charging, the estimate is usually accurate to within a few minutes, since AC sessions run at a nearly constant rate overnight. For public fast charging, treat the result as the theoretical best case and expect the final 20% to take longer. If you are budgeting household running costs, you may also find our Water Bill calculator useful for estimating other utility expenses in the same way.

Frequently Asked Questions

How do I calculate EV charging time by hand?

Multiply the battery capacity by the state-of-charge gap and divide by 100 to get the energy needed, then divide by charging power. For a 64 kWh battery going from 10% to 70%: $ 64 \times 0.6 = 38.4 $ kWh. At 7.4 kW that takes $ 38.4 \div 7.4 \approx 5.2 $ hours. To account for losses, divide the result by the efficiency, e.g. $ 5.2 \div 0.9 \approx 5.8 $ hours.

What is a good target state of charge for daily charging?

Most manufacturers recommend charging to 80–90% for daily use and reserving 100% for long trips, because high states of charge accelerate battery degradation. Many drivers also avoid dropping below 10–20%. A 20–80% routine keeps the battery in its comfort zone. This is a general guideline — check your car's manual, as chemistry-specific recommendations (especially for LFP batteries, which often tolerate 100%) vary by model.

How do I convert amps and volts to charging power in kW?

Power in watts equals current times voltage: $ P = U \times I $. A 16 A single-phase socket at 230 V gives $ 230 \times 16 = 3680 $ W, about 3.7 kW. For three-phase charging, multiply by 3: $ P = 3 \times U \times I $, so 16 A at 230 V per phase yields about 11 kW. Remember that the car's on-board charger may cap the actual rate below this.

Why does fast charging slow down above 80%?

Lithium-ion batteries absorb energy most easily between roughly 10% and 80% charge. Above that, the car progressively reduces charging current to prevent overheating and lithium plating, a protection step called tapering. A session that averages 150 kW up to 80% might drop to 40 kW or less near 100%, so the last 20% can take as long as the first 60%. This calculator's constant-power model can't capture that curve.

What is the difference between usable and gross battery capacity?

Gross capacity is the total energy physically stored in the cells, while usable capacity is what the car actually lets you charge and discharge — carmakers keep a small buffer to protect battery health. For example, a "64 kWh" battery may have only 60–62 kWh usable. Always use the usable figure from the specification sheet; if you only know the gross value, the calculator will slightly overestimate the charging time.

How much does it cost to charge my EV?

Multiply the Energy to Add result by your electricity price per kWh. If the calculator shows 40 kWh from the grid and you pay $0.15 per kWh at home, the session costs about $6. Public DC fast chargers typically charge two to four times the household rate, plus possible idle fees if you leave the car plugged in after charging finishes. Check your utility tariff or charging network's pricing for exact figures.

What are common mistakes when estimating charging time?

Frequent errors include using the charger's advertised power instead of the lower of the station's output and the car's on-board AC charger limit, ignoring charging losses (which add 5–15% to the time), using gross instead of usable battery capacity, and expecting a DC fast charger to hold its peak rate to 100%. Also remember that very cold weather can significantly slow charging, especially below 0 °C.