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How to Estimate How Long an EV Charge Takes
Heshan Fernando
Co-founder & COO
The charger says 50 kW. The battery is 64 kWh. So charging from 20% to 80% should take about 46 minutes — 38.4 kWh divided by 50.
In practice it’ll be nearer 50 minutes, and if you stay plugged in to 100% you’ll add almost as long again for the last fifth. Neither is a fault. Both follow from how batteries accept charge.
The basic calculation
time (hours) = capacity × (target% − start%) ÷ charger power
64 kWh from 20% to 80% needs 38.4 kWh. At 7.4 kW that’s 5.2 hours before losses.
Then add roughly 10% for conversion and thermal losses — energy that goes into heat in the charger, the cables and the battery rather than into storage. So about 5 hours 45 minutes for a home AC charge.
Why AC charging is slower than the charger’s rating
On AC, the limit is usually the car, not the charger. Every EV has an onboard charger that converts AC to DC, and its capacity is a fixed property of the vehicle. An 11 kW three-phase wall box delivers 7.4 kW to a car whose onboard charger is single-phase, and no cable, tariff or setting will change that.
Check the car’s onboard charger rating before assuming a faster wall box will help.
Why DC rapid charging tapers
On a rapid charger, the car’s battery management system controls the rate, and it reduces power as the battery fills to protect the cells and manage heat. The curve is steep at low states of charge and drops off substantially above about 80%.
That’s why road-trip advice is to charge to 80% and move on. The last 20% can take as long as the previous 60, and you’d generally cover more distance by driving to the next charger.
Cold weather compounds it: a cold battery accepts charge more slowly and may spend the first several minutes warming itself before rates climb at all.
| Charger | Power | 20→80% on 64 kWh |
|---|---|---|
| Home 3-pin | ~2.3 kW | ~17 hours |
| Home wall box | 7.4 kW | ~5h 45m |
| Rapid DC | 50 kW | ~50 minutes |
| Ultra-rapid DC | 150 kW+ | 20–30 min, if the car accepts it |
Why people get stuck here
- Charger rating taken as delivered power. Limited by the car on AC, by the taper on DC.
- Usable versus total capacity. Manufacturers reserve a buffer, so usable capacity is a few kWh below the headline figure.
- Losses ignored. Around 10%, more in cold weather.
- Ultra-rapid expectations. A 350 kW charger doesn’t help a car that peaks at 100 kW.
Common mistakes to avoid
- Assuming a faster wall box will speed up AC charging without checking the onboard charger.
- Planning a road trip around charging to 100% at every stop.
- Using total rather than usable battery capacity in the calculation.
- Forgetting preconditioning — many cars will warm the battery en route to a rapid charger if you navigate to it, which meaningfully improves winter charging.
- Judging a charger as faulty because it’s delivering less than its rating when the car is limiting.
How to do it with EV Charging Time Calculator
The EV Charging Time Calculator accounts for losses and flags where DC tapering makes estimates optimistic.
- Enter the usable battery capacity, a little below the headline figure.
- Set the real delivered power — for AC, that’s the car’s onboard charger limit.
- Enter the start and target state of charge.
- Treat DC estimates as optimistic above 80%, and plan road trips around 20-80% stops.
Other vehicle and energy calculators are in the tools directory.
Frequently asked questions
Why is the last 20% so slow?
Because charging tapers to protect the cells. On a rapid charger, 20 to 80% often takes less time than 80 to 100%, which is why road-trip advice stops at 80.
Why is my AC charge slower than the charger’s rating?
The car’s onboard charger sets the ceiling. An 11 kW wall box delivers 7.4 kW to a car with a single-phase onboard charger, and nothing external changes that.
Does cold weather matter?
Yes, considerably. A cold battery accepts charge more slowly and may spend the first minutes heating itself. Preconditioning on the way to a rapid charger helps if your car supports it.
Final thought
Plan around 20 to 80%, on both AC and DC. It’s where charging is fastest, where the arithmetic is most reliable, and where the battery is happiest.