EV Charging Time Calculator

EV Charging Time Calculator

What this calculator does

Electric vehicle charging time depends on more than just "how big is the battery" - it depends on how much charge you're actually adding, how fast your charger can push power into the pack, and how much of that power is lost as heat along the way. This calculator estimates:

• how long a charging session will take, from your current charge level to your target
• how much energy (kWh) you'll actually draw from the wall or charging station
• what that session will cost at your electricity rate
• how your charger compares to other common charger speeds

Why efficiency matters

Not all the power a charger draws from the grid ends up in the battery. AC charging (via the car's onboard charger) and DC fast charging both lose some energy as heat during conversion, and the amount lost depends on the charger, the car, temperature, and charge level. A charging efficiency of roughly 85-95% is typical - this calculator lets you set that value so the estimate reflects what you'll actually pay for, not just what ends up in the battery.

Formula Used

$$E_{needed} = C \times \frac{T - S}{100}$$ $$E_{drawn} = \frac{E_{needed}}{\eta}$$ $$t = \frac{E_{drawn}}{P}$$ $$cost = E_{drawn} \times rate$$

Where:

• C = battery capacity in kWh
• S = current charge level (%)
• T = target charge level (%)
• E_needed = energy that must reach the battery (kWh)
• η = charging efficiency, as a fraction (e.g. 0.9 for 90%)
• E_drawn = energy actually drawn from the source, including losses (kWh)
• P = charger power in kW
• t = charging time in hours
• rate = electricity price per kWh

Example

A 50 kWh battery charging from 20% to 80% on a 7.4 kW home wall box, with 90% charging efficiency and an electricity rate of ₹8/kWh:

$$E_{needed} = 50 \times \frac{80 - 20}{100} = 30\ kWh$$ $$E_{drawn} = \frac{30}{0.9} = 33.3\ kWh$$ $$t = \frac{33.3}{7.4} \approx 4.5\ hours$$ $$cost = 33.3 \times 8 \approx ₹267$$

So this session would take roughly 4 hours 30 minutes and cost about ₹267 - and on a 50 kW DC fast charger the same energy would take under 30 minutes, which is exactly the kind of comparison the results table shows you across common charger speeds.

Notes

• Real-world charging speed often tapers as the battery approaches 100%, especially on DC fast chargers, so times above roughly 80% target charge can run a bit longer than this straight-line estimate.
• Charger power is a ceiling, not a guarantee - your car's onboard charger or battery management system may cap the rate below what the charging point can supply.
• Use your actual electricity tariff (or a public charging network's per-kWh price) for the most accurate cost estimate.