EV Charging Time and Cost Calculator

How to use this tool

Enter the usable battery capacity in kWh, the charge level you start from and the level you stop at, then pick a charger. The list fills in the power for Level 1, Level 2 and DC fast chargers. For any other charger choose an "Other" entry and type the kW, or choose volts and amps and the tool multiplies them and divides by 1,000. If the car cannot accept what the charger offers, put its limit in the optional box, because the slowest link sets the speed. Prices, fuel use and yearly distance start as examples that give round numbers, not anyone's tariff, so replace them.

The input people most often get wrong is the car's energy use. A trip computer shows what the battery supplies, but EPA label figures are measured at the wall and already include charging losses. If you type a label figure, set the box to "At the wall, with losses", or the tool takes the losses off twice. Use the usable battery capacity too, which can be lower than the headline figure.

What the calculation is doing

Energy into the battery is capacity times the change in charge: 60 × 0.60 = 36 kWh for 60 kWh from 20 to 80 percent. The wall supplies more, because the cable, charger and car lose some as heat. Wall energy = battery energy ÷ efficiency, so 36 ÷ 0.90 = 40 kWh, and that is what you pay for. On an AC charger the battery receives charger power × efficiency, so time = 36 ÷ (7.2 × 0.90) = 5.56 hours, or 5 h 33 min. Charger power is volts × amps ÷ 1,000: 240 V at 30 A is 7.2 kW.

DC fast chargers are treated differently. Their rated power is delivered at the plug, so the car receives it directly, and the 95 percent default efficiency only sets how much the wall supplies. The slowdown near full is modelled in two stages: full power up to 80 percent, then a share of it that you can edit, starting at 25 percent. No source gives that share for current cars, so 25 percent is an assumption.

Cost is wall energy × price, and range added is battery energy ÷ the car's energy use. L per 100 km = 100 × 3.785411784 ÷ (1.609344 × mpg), which is 235.215 ÷ mpg for US gallons and 282.481 ÷ mpg for imperial gallons. MPGe uses 33.705 kWh per gallon. A charger is a continuous load, so its circuit is rated at least 125 percent of the charger current: 30 A needs 37.5 A.

Why home charging is slow but cheap

Home charging is slow because it can be. A car parked for ten hours on a 7.2 kW charger takes in about 65 kWh, enough to fill a 60 kWh battery from empty. Even a 1.9 kW Level 1 outlet adds 12 kWh in 7 h 1 min, which is 75 km at 16 kWh per 100 km. The US Department of Energy puts Level 1 at about 5 miles of range per hour and Level 2 at about 25, and Natural Resources Canada gives 3 to 8 km and 16 to 50 km. A household outlet tops up, and a 240 V circuit refills.

The cost is the energy: kWh from the wall times your price. Losses are the hidden part. The Idaho National Laboratory measured 88.8 percent from wall to battery on Level 1 and 90.8 percent on Level 2 for one car, and a California study found 91 to 93 percent for AC chargers and 95 to 97 percent for DC. The German motoring club ADAC measured losses of 12.7 to 24.2 percent on a 2.3 kW household socket against 5.1 to 7.0 percent on an 11 to 22 kW wallbox. Efficiency therefore runs from about 76 to 95 percent, and the low end is slow charging.

At the default 90 percent, 4 of the 40 kWh you buy never reach the battery, which costs 0.60 at the example price. With the 24.2 percent loss ADAC saw on a socket, the same charge draws 47.5 kWh, and over 15,000 km at 16 kWh per 100 km the extra against the default is about 500 kWh a year, or 75 at 0.15 per kWh.

The slowest link sets the speed, and the last 20 percent is slow

Rated power is a ceiling. The circuit, cable, charger, onboard charger and battery each have a limit, and the lowest wins. An 11.5 kW wallbox on a car that accepts 7.4 kW delivers 7.4 kW, so the 60 kWh charge takes 5 h 24 min instead of 3 h 29 min. On DC, a 350 kW station and a car that takes 150 kW give 150 kW.

The battery also limits itself as it fills. The EPA says many current vehicles drop to extremely low rates of charge after about 80 percent, and Natural Resources Canada bases its times on an 80 percent limit. Idaho National Laboratory tests of a 2013 Nissan Leaf, an old air cooled pack, showed peaks of 20 to 40 kW but an average of 0.6 to 3.6 kW in the top off phase. Newer cars taper less harshly, but no source gives a general figure, so the tool asks you for one. With the default 25 percent, 60 kWh from 10 to 80 percent at 150 kW takes 17 min, and the last 20 percent takes another 19 min.

Range per hour is the number to plan around. At 7.2 kW and 16 kWh per 100 km the default car gains 40.5 km, about 25 miles, an hour, which matches the DOE figure. Cold changes the arithmetic. Fueleconomy.gov, citing a 2019 AAA study, says EV fuel economy at 20 °F is 8 percent lower than at 75 °F without cabin heat and about 39 percent lower with the heater on. A 39 percent drop raises energy per km by about 64 percent, so entering 26.2 kWh per 100 km instead of 16 moves the cost per 100 km from 2.67 to 4.37.

Charging time and circuit size for common chargers

The first table shows 60 kWh from 20 to 80 percent at 90 percent efficiency on AC and 95 percent on DC, with 16 kWh per 100 km and the example price of 0.15 per kWh.

The second table applies the continuous load rule at 240 V. It is a minimum, and the next standard breaker size up is used.

A worked example you can check on paper

Default view: 60 kWh usable, 20 to 80 percent, 7.2 kW Level 2, 90 percent efficiency, 0.15 per kWh. Battery energy = 60 × (80 − 20) ÷ 100 = 36 kWh. Wall energy = 36 ÷ 0.9 = 40 kWh. Power into the battery = 7.2 × 0.9 = 6.48 kW. Time = 36 ÷ 6.48 = 5.556 h = 5 h 33 min. Cost = 40 × 0.15 = 6.00.

Driving, at 16 kWh per 100 km at the battery: wall energy per 100 km = 16 ÷ 0.9 = 17.78 kWh, so cost per 100 km = 17.78 × 0.15 = 2.67. Range added = 36 ÷ 16 × 100 = 225 km, and per hour = 6.48 ÷ 16 × 100 = 40.5 km. Petrol at 8 L per 100 km and 1.60 per litre costs 8 × 1.60 = 12.80 per 100 km, so 225 km costs 28.80 and the charge saves 22.80. Over 15,000 km a year that is 400.00 against 1,920.00, a saving of 1,520.00. Petrol matches electricity at 12.80 ÷ 17.78 = 0.72 per kWh. The circuit: 7,200 W ÷ 240 V = 30 A, times 1.25 = 37.5 A, so a 40 A circuit.

DC check: 60 kWh from 10 to 100 percent at 150 kW with 25 percent of power above 80 percent. Up to 80 percent is 42 kWh ÷ 150 kW = 0.28 h = 16.8 min. Above 80 percent is 12 kWh ÷ (150 × 0.25) kW = 0.32 h = 19.2 min. The total is 36 min.

Mistakes that catch people out

Using the headline battery size. Time and cost scale with usable capacity, not the brochure figure.

Counting the losses twice. Label figures are already measured at the wall. Typing 25 kWh per 100 miles with the box on "At the battery" and 90 percent efficiency gives 27.8 kWh per 100 miles at the wall, about 11 percent too high. Switch the box to "At the wall, with losses".

Trusting the rated kW. An 11.5 kW wallbox charges a car that accepts 7.4 kW no faster than a 7.4 kW one does. Enter the car's limit.

Planning around 100 percent. With the default taper, the last 20 percent on a DC charger takes longer than the first 70. Plan a stop around range per hour up to 80 percent.

Sizing the breaker at the charger current. A 32 A charger on a 32 A breaker breaks the continuous load rule, because it needs 40 A. Wire size, panel capacity and permits are for a licensed electrician.

Popular calculations

Each opens the calculator with those figures filled in, and they can be changed once it is open. The prices in them are examples.

Level 1 overnight

Level 2 home chargers

DC fast charging examples

Battery sizes from 40 to 100 kWh

Cost per 100 km against petrol

How this was checked

The engine was tested in a separate script. Wall energy × efficiency equals battery energy, and battery energy equals capacity times the change in charge, on 5,000 random inputs with the worst error at the limit of double precision. Charge time matched an independent calculation that steps through the state of charge in 20,000 slices and adds up the time, on 5,000 random AC and DC cases, within 0.02 percent. Time rose with every extra percent and fell with every extra kW, on 2,000 cases each, and doubling the power halved it.

The constants come from NIST: the US gallon is 231 cubic inches, 3.785411784 litres, the mile is 1.609344 km, and the imperial gallon is 4.54609 litres (Handbook 44 and SP 811). L per 100 km to mpg and back returned the start on 5,000 random values in both gallons. 30 US mpg gave 7.84 L per 100 km and 30 imperial mpg gave 9.42, matching the 7.8 and 9.4 that Wikipedia gives as a cross check.

Against published data: the EPA gallon is 33.705 kWh, and applying it to the fueleconomy.gov MPGe of 137, 128, 131, 109 and 142 for five Tesla Model 3 entries gives 24.6, 26.3, 25.7, 30.9 and 23.7 kWh per 100 miles, which round to the 25, 26, 26, 31 and 24 on the site. The Idaho National Laboratory Volt test multiplies 91.7 percent by 99 percent to get 90.8, and 90.6 by 98 to get 88.8, its published totals. The DOE figures of 7.2, 2.9 and 19.2 kW are 240 V × 30 A, about 240 V × 12 A and 240 V × 80 A. The 125 percent rule turns 32 A into 40 A and 30 A into 37.5 A, which is why IAEI pairs 30 A chargers with 40 A circuits. With the 25 kWh per 100 miles label figure of a 2025 Model 3 Long Range RWD entered at the wall on 6.6 kW, the tool gives 26 miles per hour, against about 25 from the DOE and EPA.

Where sources disagree, both are shown. Natural Resources Canada lists Level 1 as 8 to 50 hours or more on one page and 8 to 16 on another, and Level 2 as 4 to 10 hours and 4 to 6. The spread is mostly battery size: 8 and 50 hours at 1.9 kW and 90 percent fill batteries of about 17 and 107 kWh to 80 percent, which is arithmetic from those two inputs, not a figure either source states. The EPA uses 6.6 kW for Level 2 and the DOE 7.2 kW. The limits are these. No source gives the share of power above 80 percent for current cars. The DC efficiency covers the charger, not battery conditioning. The circuit rule is guidance, not an installation design. The code rules are as reported by Electrical Construction and Maintenance magazine, IAEI and Electrical Industry, not read from the paywalled code books, and the ADAC and California figures come from news reports and project summaries, not the full studies.

Every address in the lists above was then opened and checked for a distinct title, the right answer, a chart that renders, and clean CSV, image and print output containing only the values entered.

Common questions

How long does it take to charge an electric car?

It is the energy going into the battery divided by the power going into it. For 20 to 80 percent of a 60 kWh battery, a 1.9 kW Level 1 outlet takes 21 h 3 min, a 7.2 kW Level 2 charger 5 h 33 min and a 150 kW DC fast charger 14 min.

How much does it cost to charge an electric car at home?

Multiply the kWh drawn from the wall by your price per kWh. Putting 36 kWh into the battery at 90 percent efficiency draws 40 kWh, so at the example price of 0.15 per kWh it costs 6.00 and adds 225 km.

Why does EV charging slow down after 80 percent?

The car cuts the charging current as the battery fills. The EPA says many current vehicles drop to extremely low rates of charge after about 80 percent. The tool lets you edit the share of rated power used above 80 percent.

What size circuit does an EV charger need?

A charger is a continuous load, so under US National Electrical Code Article 625 the circuit is rated at least 125 percent of the charger current. A 30 A charger at 7.2 kW needs 37.5 A, which means a 40 A circuit. The Canadian Electrical Code limits a continuous load to 80 percent of the rating, which is the same rule.

Is charging an electric car cheaper than petrol?

Compare the cost per 100 km. With the example figures, electricity costs 2.67 once losses are counted, against 12.80 for petrol. Petrol only matches electricity at 0.72 per kWh, and the tool works out that break even price for your own numbers.

How much does cold weather cut EV range?

Fueleconomy.gov, citing a 2019 AAA study, says range at 20 °F is about 12 percent lower than at 75 °F without cabin heat and 41 percent lower with the heater on, and that preheating while plugged in helps. The tool has no temperature box, so raise the kWh per 100 km figure and read the cost again.

Related Calculators and Reference

• Electricity Cost Calculator: what any appliance costs to run, to check your price per kWh.
• Gas Cost Calculator: the fuel cost of a petrol trip.
• Fuel Economy Converter: switch a car's figure between mpg and L per 100 km.
• Watts to Amps Calculator: turn a charger's kW into amps.
• Voltage Drop Calculator: check the wire run to the charger.
• Solar Panel Calculator: size panels for the kWh a car uses each year.
• US Department of Energy Alternative Fuels Data Center: charging levels, power and range.