EV Charging Time

Calculating Your EV Charging Time

Charging time equals the energy that still needs to be added to the battery, divided by how fast the charger can actually deliver it. Enter your EV’s battery capacity, its current and target charge levels, your charger’s rated power, and a charging efficiency estimate, and this calculator returns how long the session should take and how much energy it will add.

This is distinct from the EV Charging Cost Calculator calculator, which estimates what charging costs rather than how long it takes, and the EV Range Calculator calculator, which estimates how far the result will get you rather than how long it takes to get there.

Key Factors to Consider

• The vehicle’s own onboard charger has its own maximum power rating, separate from the charger’s rated output. For AC (home/Level 2) charging, the slower of the two limits — the wallbox’s rated power, or the car’s onboard charger limit — governs the actual charging speed. A vehicle with a lower onboard charger limit than the wallbox it’s plugged into won’t charge any faster than its own limit allows, regardless of what the charger itself is rated for.
• Battery temperature affects real charging speed, especially on DC fast chargers. A cold battery charges more slowly than a warm one — this is part of why some EVs precondition (pre-warm) the battery automatically when a fast-charging stop is set as a navigation destination, to charge faster once plugged in.
• Even within the 20-80% range, DC fast-charging speed isn’t perfectly constant. Real charging curves ramp up and taper gradually rather than holding one flat rate the whole time — this calculator’s constant-effective-rate assumption is a reasonable simplification, but an individual session’s actual timing can vary somewhat from the estimate for this reason.

The Formula

$$\vB{\text{kWh Added}} = \vA{\text{Battery Capacity}} \times \left(\frac{\vD{\text{Target Charge \%}} - \vC{\text{Current Charge \%}}}{100}\right)$$ $$\vF{\text{Effective Rate}} = \vE{\text{Charger Power}} \times (\vG{\text{Charging Efficiency \%}} \div 100)$$ $$\text{Charging Time} = \frac{\vB{\text{kWh Added}}}{\vF{\text{Effective Rate}}}$$

Worked Example

A 75 kWh battery charging from 20% to 80%, on a 7 kW charger at 90% efficiency:

1. kWh Added: $\vA{75} \times \left(\frac{\vD{80} - \vC{20}}{100}\right) = \vB{45} \text{ kWh}$.
2. Effective Rate: $\vE{7} \times (\vG{90} \div 100) = \vF{6.3} \text{ kW}$.
3. Charging Time: $\vB{45} \div \vF{6.3} \approx 7.14 \text{ hours}$, or about 7 hours 9 minutes.

Common Mistakes

• Assuming DC fast-charging speed stays constant all the way to 100%. As covered above, most EVs taper their charging rate well before a full battery to protect battery health — charging to 100% on a fast charger almost always takes noticeably longer per added kWh than the 20-80% portion of the same session.
• Using the charger’s rated power instead of the vehicle’s onboard charger limit for home (AC) charging. A wallbox rated at 11 kW plugged into a car with a 7.4 kW onboard charger will only ever charge at 7.4 kW — the slower of the two limits always wins, regardless of what the charger itself is capable of delivering.
• Ignoring charging efficiency entirely. As noted above, some energy is always lost as heat during AC-to-DC conversion — treating the charger’s rated power as the effective rate (100% efficiency) will underestimate how long a real session actually takes.
• Assuming charging speed is unaffected by temperature. A cold battery accepts charge more slowly than a warm one, particularly on DC fast chargers — a charging session on a cold morning can genuinely take longer than the same session in mild weather, even with identical inputs.

Useful to Know

• If your vehicle’s owner’s manual lists an onboard AC charger limit, use whichever of that figure or the charger’s rated power is lower as your effective charging rate — this calculator’s charger power field should reflect that smaller number for a home/Level 2 session.
• Many DC fast chargers display or publish their actual delivered kilowatts partway through a session, which is often lower than the charger’s maximum rating once other vehicles share the same station or the battery’s charge curve has started to taper.
• This calculator pairs naturally with EV Charging Cost Calculator (what that same charging session will cost) and EV Range Calculator (how far the added charge will actually take you) for a more complete picture of a single charging stop.