EV Charge Time Calculator

Charge time is the calculation people run first and misread most often, because two different numbers both call themselves the charger. The unit on the wall has a maximum output. Your car has an onboard AC charger with its own maximum. Charging happens at whichever is lower, and in the majority of households it is the car.

The arithmetic itself is simple. Energy needed divided by power delivered, adjusted for the fact that charging is not perfectly efficient. Getting from 20 percent to 80 percent of a 75 kWh pack means moving 45 kWh into the battery, which at 9.6 kW and 90 percent efficiency takes about five hours.

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Charge time

kWh / kW

Enter your pack size, your charger output and the state of charge you are starting from. The calculator caps power at your vehicle's onboard charger limit, because that is what actually happens.

Usable battery capacity

Usable, not gross. It is on the window sticker and in the manual.

kWh

Charger output 1.4 kW, 120 V at 12 A, Level 1 1.9 kW, 120 V at 16 A, Level 1 3.8 kW, 240 V at 16 A 5.8 kW, 240 V at 24 A, dryer circuit 7.7 kW, 240 V at 32 A 9.6 kW, 240 V at 40 A, NEMA 14-50 11.5 kW, 240 V at 48 A, hardwired 19.2 kW, 240 V at 80 A

Vehicle onboard charger limit

The ceiling your car can accept. This is usually the binding constraint.

3.6 kW, many plug-in hybrids 6.6 kW, Nissan Leaf, early Toyota bZ4X 7.2 kW 9.6 kW 10.9 kW, Hyundai Ioniq 5, Kia EV6 11.5 kW, most current EVs 19.2 kW, F-150 Lightning with the right equipment

Starting charge

%

Target charge

%

Vehicle efficiency

mi per kWh

Charging time

5.0 hours

About 5 h 0 min

Energy into the pack

45.0 kWh

Actual charging power

9.6 kW

Range added per hour

34 miles

Range added in total

158 miles

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Why the car is usually the limit, not the charger

An electric car does not plug into AC power directly. Alternating current from the wall goes through an onboard charger inside the vehicle, which converts it to the direct current the battery needs. That converter has a fixed maximum rating, and it is the smallest number in the chain in most households.

This is why the wall unit's rating is frequently irrelevant. A 48 amp station can supply 11.5 kW. A Nissan Leaf accepts 6.6. Connect the two and you charge at 6.6 kW, having paid for a 60 amp circuit to deliver power the car declines. It is the most common way people overspend on a home installation.

Read the last two columns together. For the cars limited to 6.6 kW the two figures are identical, because the extra supply changes nothing. For the rest the 48 amp circuit saves roughly 45 minutes on a full overnight charge, and the honest question is whether 45 minutes of an eight hour window you are asleep for is worth several hundred dollars. Usually it is not, unless you are wiring the circuit anyway, which is the argument made in the hardwired 48 amp buildout.

The arithmetic, in full

Four steps, none of them difficult, and worth seeing so you can sanity check any figure you are given.

1. Energy needed. Pack size multiplied by the percentage gap. A 75 kWh pack going from 20 to 80 percent needs 75 times 0.60, which is 45 kWh.
2. Power delivered. The lower of the charger output and the vehicle's onboard limit. A 9.6 kW charger and an 11.5 kW car gives 9.6 kW.
3. Efficiency. Multiply the power by roughly 0.90 for Level 2. Some energy becomes heat in the onboard charger, the cable and the thermal management system.
4. Divide. 45 kWh divided by 8.64 kW effective is 5.2 hours.

Notice that step three matters more than people expect. Ignoring efficiency understates every charge time by about ten percent, and on Level 1 the error is worse because the fixed overheads of running the vehicle's systems are a much larger fraction of a 1.4 kW input.

What each circuit size means in practice

The row that surprises people is the 24 amp one. A dryer circuit shared through a listed splitter device gives 5.8 kW, which is around 18 miles per hour, or 145 miles over an eight hour night. For a driver covering 40 miles a day that is three times more than needed, and it requires no new circuit at all.

How much charging speed do you actually need?

Work backwards from your driving rather than forwards from the hardware. The question is not "how fast can I charge" but "can I replace what I used in the window the car is parked".

An average American driver covers around 37 miles a day. At 3.5 miles per kWh that is 10.6 kWh, which takes about 70 minutes at 9.6 kW and about 7.5 hours on a standard 120 volt outlet. Both fit comfortably in an overnight window. Level 1 stops working when daily mileage passes roughly 40 miles, or when the car sits for shorter periods.

The genuinely useful figure is your worst normal day, not your average. If you occasionally drive 180 miles and come home at 8pm needing to leave at 6am, you need 51 kWh back in ten hours, which is 5.7 kW of actual charging power. A 32 amp charger covers it. Almost nobody needs the top of the range, and the Level 1 against Level 2 comparison works through where the genuine break point sits.

Things that make real charge times longer than the calculator

Cold weather

A cold pack may be heated before or during charging, and that energy comes from the same supply. In deep cold a session can take 25 percent longer. Scheduling the charge to finish shortly before departure, rather than starting it the moment you plug in, lets the car precondition on wall power instead of on the battery.

The last ten percent

Even on AC, most cars slow slightly above 90 percent, and many run cell balancing after reaching the target. If the display sits at 99 percent for twenty minutes, that is normal and it is not a fault.

Voltage drop on a long run

A charger at the end of an undersized 100 foot run sees reduced voltage, and reduced voltage at the same current is reduced power. A three percent drop costs about three percent of your charging speed, every session, forever. Check yours with the voltage drop calculator before the conductor is buried in a wall.

Shared circuits and load management

If your charger is behind a load management device, it will throttle when the house draws heavily. That is the device doing its job, and it usually costs less charging time than people fear because household peaks are short. It is also frequently what makes the circuit possible at all.

Where to go next

If the time this calculator returns fits your overnight window, you do not need a bigger circuit and you should read the plug-in buildout. If it does not, size the circuit on the breaker size calculator, check the panel with the panel load calculator, and price the job with the installation cost calculator. To know what the energy costs, use the charging cost calculator.

Common questions

How long does it take to charge an EV at home?

On a 40 amp Level 2 charger delivering 9.6 kW, a typical 75 kWh pack goes from 20 to 80 percent in roughly five hours. On a 48 amp charger at 11.5 kW the same charge takes about four and a quarter hours. On a standard 120 volt outlet at 1.4 kW it takes about 36 hours, which is why Level 1 only works for short daily commutes and plug-in hybrids.

Why does my car charge slower than the charger is rated for?

Almost always because the car, not the charger, is the limit. Every electric vehicle has an onboard AC charger with a fixed maximum, commonly 7.2, 11 or 11.5 kW, and it will only draw up to that figure no matter what the wall unit can supply. A Nissan Leaf on a 48 amp station charges at 6.6 kW because that is what its onboard charger accepts.

Should I charge to 100 percent every night?

Generally no. Most manufacturers recommend a daily limit around 80 percent for lithium-ion packs and reserve full charges for trips, because time spent at a high state of charge accelerates degradation. Lithium iron phosphate packs are the exception and several makers recommend a periodic full charge for them. Follow your own manufacturer, not a general rule.

Why does charging slow down near the top?

At AC charging speeds this effect is small, because the onboard charger is already well below the rate at which the battery management system needs to taper. You may see the last few percent slow, and the car may run cooling or balancing after reaching the target. Dramatic tapering is a DC fast charging phenomenon, not a home charging one.

Does cold weather change home charging time?

Yes, though less than it changes range. A cold pack may be warmed before or during charging, and that energy comes out of the same supply, so a session that normally takes four hours can take five or more in deep cold. Preconditioning while still plugged in is the usual fix, and it is one of the few genuinely useful features of a scheduled charge.

What efficiency figure should I use?

Charging is not lossless. Some energy is lost in the onboard charger, in cable resistance and in thermal management, so the pack receives less than the meter records. Around 90 percent is a reasonable planning figure for Level 2 and this calculator uses it. Level 1 charging is noticeably worse, often 80 to 85 percent, because the overheads are a larger share of a smaller input.

Getting your own panel and load numbers ready for an electrician? The EV Home Charging Install Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.