EV Charging Time Calculator
Enter battery kWh and charger kW to get charging time, grid energy drawn (including losses), range added and cost — for Level 1 through DC fast.
Last updated: 2026-09-15
How the calculation works
- The charge window (e.g. 20→80%) selects the energy actually needed, not the whole battery.
- Charging losses (on-board charger + battery thermal management) inflate the grid draw by ~10%.
- Time divides energy by charger power; range and cost follow from vehicle efficiency and your rate.
Formula
Energy = battery kWh × charge window ÷ efficiency Time = energy ÷ charger kW
| Symbol | Meaning | Unit |
|---|---|---|
E | Energy needed | kWh |
P | Charging power | kW |
η | Charging efficiency | — |
Worked example
Interpreting the result
The 20–80% window is the EV owner's sweet spot: fastest charging, least battery wear, and DC fast-charging tapers hard above 80% (the last 20% can take as long as the first 60%). Level 1 (1.4 kW) adds only ~4–5 miles per hour — fine overnight, useless for quick top-ups.
Assumptions
- Constant charging power through the window — real DC charging tapers with SOC.
- Battery thermal conditioning is included in the efficiency figure.
Limitations
- Cold weather can halve DC charging speed until the battery warms.
- Shared circuits, derated cables and vehicle limits may reduce power below the charger's rating.
Frequently asked questions
How long to charge an EV at home?
With a 7.2 kW Level 2 charger, most EVs go 20–80% in 5–8 hours. Level 1 (wall outlet) takes 3–4× longer — fine if the car sits all night.
Why does DC charging slow down above 80%?
Lithium cells accept charge current based on their internal voltage headroom; as they approach full, that headroom shrinks and the BMS cuts current to prevent lithium plating. Charging to 100% is inherently slow.