EV Charging Time Calculator
Estimate how long a charging session takes from the pack size, the state-of-charge window, and the charger you are plugged into.
Results
Charging time: 6 h
Energy added to the battery: 39 kWh
Power actually reaching the battery: 6.48 kW
Energy you pay for: 43.33 kWh
How it works
Energy needed divided by the power that actually reaches the battery. At home the charger's rating is AC, so part of it is lost in conversion; a DC fast charger's rating is already the DC power going into the pack.
kwh_to_add = battery_kwh × (target_soc − current_soc) / 100
power_to_battery = charger_kw × metered_efficiency
hours = kwh_to_add / power_to_battery
battery_kwh- Usable pack energy in kWh — not the gross or nameplate figure.
current_soc / target_soc- Start and finish state of charge, in percent.
charger_kw- Rated charger output in kW.
metered_efficiency- Share of delivered energy reaching the battery: 0.85 on Level 1, 0.90 on Level 2, 1.00 on DC fast. Shared with the charging cost tool.
power_to_battery- charger_kw × metered_efficiency — the useful power.
hours- kwh_to_add ÷ power_to_battery.
Assumptions
- The 65 kWh default is an illustrative mid-size pack, not a measurement. There is no car model dropdown because usable pack energy is not published consistently — Tesla does not publish it at all, and EPA's vehicle records return no battery figure for the EVs we checked.
- The estimate assumes steady power for the whole session. That holds well for Level 1 and Level 2: the onboard charger draws roughly constant power from nearly empty to nearly full, which is why overnight charging times are predictable.
- It does not hold on DC fast charging. Somewhere in the 70–80% region the battery management system cuts current to protect the cells, so the last stretch takes far longer than a flat estimate suggests. Peak kW is also a number most cars hold only briefly near the bottom of the curve.
- On Level 1 and Level 2 the car's onboard charger sets the ceiling. An 11 kW onboard charger will draw 11 kW from a 19.2 kW unit, not 19.2 kW. Enter whichever is lower.
- Level 1 0.85 and Level 2 0.90 are rounded from a field study of 115 real sessions. DC fast uses 1.00 because the dispenser's rating is already DC power going into the pack.
- Cold packs charge slower and spend energy on preconditioning. A freezing winter session can run well past the estimate.
FAQ
How long does it take to charge an EV at home?
Going from 20% to 80% on a 65 kWh pack means adding 39 kWh. A typical 7.2 kW home Level 2 unit delivers about 6.5 kW to the battery after conversion loss, so roughly 6 hours — an ordinary overnight charge. The same top-up on a 120 V outlet takes about 33 hours, which is why Level 1 only suits small daily top-ups.
Why does the last 20% take so long on a fast charger?
As the pack fills, cell voltage rises and the battery management system cuts current to avoid lithium plating. Charging power steps down repeatedly somewhere above 70–80%, so the final stretch can take as long as everything before it. On a road trip it is usually faster to stop at 80% and drive on.
Will a bigger home charger charge my car faster?
Only up to your car's onboard charger. That unit does the AC-to-DC conversion and sets the ceiling: a car with an 11 kW onboard charger draws 11 kW from a 19.2 kW wall unit. Check the onboard charger rating before paying for a larger circuit.
Sources
- U.S. DOE Alternative Fuels Data Center — Electric Vehicle Charging Stations (Level 1 / Level 2 / DC fast power ratings; captured 2026-09)
- Sears et al., "A comparison of electric vehicle Level 1 and Level 2 charging efficiency" (IEEE, 2014) — Level 1 83.8%, Level 2 89.4% across 115 logged sessions
- U.S. DOT Rural EV Toolkit — Charging Speeds: DC fast charging reaches 80% in 20 minutes to 1 hour, the window manufacturers quote precisely because the curve tapers above it
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