Why is actual DC fast charging sometimes slower?

Power tapers at higher SOC and depends on temperature and vehicle acceptance. This model assumes constant power.

Can I use this for Level 1 or Level 2?

Yes. Enter the charger kW (e.g., ~1.4 kW for Level 1 at 120V/12A, ~7–12 kW for many Level 2 setups).

What about usable vs gross battery?

Use usable capacity for a closer match; gross capacity may overstate available energy.

Does weather affect losses?

Cold weather can increase losses and slow charging. Increase loss % if charging in cold conditions.

Does this include preconditioning time?

No. It only models the charge energy/time, not preconditioning duration.

tech calculator

EV Charging Time Calculator

Estimate how long it takes to charge an EV from a start % to a target % at a given charger power.

Results

Energy needed (kWh): 52.50
Energy including losses (kWh): 58.33
Estimated charge time (hours): 5.30
Estimated charge time (minutes): 318.18

How to use this calculator

Enter your EV battery capacity in kWh.
Set start % and target % for the charge.
Enter charger power (kW) and an estimated loss %, then view charge time in hours/minutes.

Inputs explained

Battery capacity: Gross/usable battery size in kWh.
Start/Target SOC: Current and desired battery percentage.
Charger power: AC Level 1/2 or DC fast charge power in kW.
Charging loss: Percent energy lost to heat/conversion; 5–15% is common.

How it works

Energy needed = Battery capacity × (Target % − Start %) / 100.

We add a loss factor to account for charging inefficiency.

Charge time = Energy (with loss) ÷ Charger power.

Formula

Energy needed = Battery kWh × (Target − Start)/100
Energy incl. loss = Energy needed ÷ (1 − Loss)
Charge time (hours) = Energy incl. loss ÷ Charger kW

When to use it

Planning home Level 2 charging overnight.
Estimating DC fast charge time from a low state of charge.
Checking how long a top-up to 80% might take on a road trip.

Tips & cautions

DC fast charging often tapers above ~60–80%; this simple model assumes constant power—real times may be longer at high SOC.
Use the charger’s advertised kW, but actual power can be lower depending on vehicle acceptance and temperature.
Adjust loss % based on your car/charger; cold weather and AC charging may have higher losses.
Does not model charging taper; actual fast-charge times at high SOC may be longer.
Assumes constant charger power and fixed loss rate.
Ignores preconditioning and battery temperature effects.

Worked examples

75 kWh pack, 10% to 80% on 11 kW AC, 10% loss

Energy needed = 75 × (80−10)/100 = 52.5 kWh
With loss ≈ 52.5 ÷ 0.9 ≈ 58.3 kWh
Time ≈ 58.3 ÷ 11 ≈ 5.3 hours (≈ 319 minutes)

82 kWh pack, 20% to 70% on 150 kW DC, 8% loss

Energy needed = 82 × 0.5 = 41 kWh
With loss ≈ 44.6 kWh
Time ≈ 44.6 ÷ 150 ≈ 0.30 hours (≈ 18 minutes, taper not modeled)

Deep dive

Estimate EV charging time by entering battery size, start/target %, charger kW, and loss to see hours and minutes required.

Use it for home Level 2 planning or quick DC fast-charge estimates (taper not modeled).

FAQs

Why is actual DC fast charging sometimes slower?: Power tapers at higher SOC and depends on temperature and vehicle acceptance. This model assumes constant power.
Can I use this for Level 1 or Level 2?: Yes. Enter the charger kW (e.g., ~1.4 kW for Level 1 at 120V/12A, ~7–12 kW for many Level 2 setups).
What about usable vs gross battery?: Use usable capacity for a closer match; gross capacity may overstate available energy.
Does weather affect losses?: Cold weather can increase losses and slow charging. Increase loss % if charging in cold conditions.
Does this include preconditioning time?: No. It only models the charge energy/time, not preconditioning duration.

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Simplified constant-power estimate. Real-world charging varies with taper, temperature, and vehicle limits. Use manufacturer data for trip-critical planning.