Electric Car Charging Calculator: Cost & Time

This calculator works out how much it costs to charge an electric vehicle and how long the charge takes, based on your battery size, charger power, electricity rate, and starting and target charge levels. You enter your car’s usable battery capacity, the charger’s power output, your electricity price per kWh, and your current and desired state of charge; you get back the energy needed, the charging time, and the total cost. It uses the standard physics of battery charging, so you can compare home, workplace, and public charging scenarios.

Formula

The core formula is simple: energy needed (kWh) equals battery capacity (kWh) multiplied by the percentage increase in state of charge (as a decimal). Then time equals energy divided by charger power, and cost equals energy multiplied by the electricity rate.

E = energy needed (kWh)
C = usable battery capacity (kWh)
S_start = starting state of charge (%)
S_target = target state of charge (%)
P = charger power (kW)
R = electricity rate ($/kWh)
t = charging time (hours)

E = C × (S_target − S_start) / 100

t = E / P

Cost = E × R

Worked Example

Using the default values: a 60 kWh battery, charging from 20% to 80% on a 7.4 kW home charger at $0.15/kWh.

Charge percentage increase: 80 − 20 = 60%
Energy needed: 60 kWh × 60 / 100 = 36 kWh
Charging time: 36 kWh ÷ 7.4 kW = 4.86 hours (about 4 hours 52 minutes)
Cost: 36 kWh × $0.15/kWh = $5.40

The calculator shows 4.86 hours, 36.0 kWh, and $5.40, matching the hand calculation.

Understanding the Inputs

Each input matters, and getting them right avoids surprises.

Battery capacity (kWh): Use the usable capacity, not the total. Many EVs reserve a small buffer to protect the battery, so the usable figure is often 2–5 kWh lower than the advertised total. Check your owner’s manual or the vehicle’s display.
Starting and target charge (%): Most drivers charge from around 20% to 80% for daily use, because charging above 80% slows down significantly on DC fast chargers and is harder on the battery if left that way for long periods. For a road trip, you might target 100%.
Charger power (kW): This is the output of the charger, not the input. A standard home outlet (120 V) delivers about 1.2–1.9 kW; a Level 2 home charger is typically 7.4 kW (240 V, 32 A) or 11 kW (three-phase in some regions); public DC fast chargers range from 50 kW to 350 kW.
Electricity rate ($/kWh): Your home rate may be a flat rate or a time-of-use rate (cheaper at night). Public chargers often charge per kWh, per minute, or a combination. Use the actual rate you pay.

How to Choose Your Charging Setup

Use the calculator to decide what charger fits your routine. For example, if you drive 40 miles per day and your car uses about 0.25 kWh per mile, you need roughly 10 kWh per day. On a 7.4 kW charger, that’s about 1.4 hours. A 3.7 kW charger would take 2.7 hours. If you have an overnight window of 8 hours, even a 3.7 kW charger is plenty for typical daily driving.

For occasional long trips, DC fast charging time matters. Charging from 20% to 80% on a 60 kWh battery needs 36 kWh. On a 50 kW charger, that’s 43 minutes; on a 150 kW charger, about 14 minutes (but real fast charging tapers, so it will be longer). The calculator gives the ideal lower bound—actual times are higher because the charging power drops as the battery fills.

Common Mistakes and Real-World Limits

The formula assumes constant power, but real charging is not perfectly linear. Three factors make actual times longer:

Charging taper: Lithium-ion batteries charge fastest in the middle of their range. Above 80%, power drops significantly to protect the battery. A 150 kW charger might deliver only 50 kW at 90% state of charge.
Losses: About 5–15% of energy is lost as heat during AC charging. The calculator’s energy figure is what goes into the battery; the wall will draw more. For cost, multiply by 1.1 to 1.15 for a realistic estimate.
Temperature: Cold batteries charge slower. In winter, expect 20–30% longer times on DC fast chargers unless the battery is pre-conditioned.
Rated vs. actual power: A 7.4 kW charger may deliver 7.0 kW due to voltage drop and onboard charger limits.

Another common mistake is using the car’s total battery capacity instead of usable capacity. If you use 75 kWh instead of 70 kWh, your time and cost are about 7% too high.

Cost Comparisons: Home vs. Public

The calculator lets you compare scenarios side by side. For a 60 kWh battery charging from 20% to 80%:

Home at $0.15/kWh: $5.40
Home at $0.30/kWh (peak time-of-use): $10.80
Public Level 2 at $0.30/kWh: $10.80
DC fast charger at $0.48/kWh: $17.28

Home charging is almost always cheaper, especially overnight. Some utilities offer special EV rates as low as $0.08/kWh. Public fast charging is convenient but can cost more than gasoline per mile in some regions.

To compare with a gasoline car, use the energy cost per mile. If your EV gets 3.5 miles per kWh (about 0.29 kWh/mile), then at $0.15/kWh, the cost per mile is $0.043. A gas car getting 30 mpg at $3.50/gallon costs $0.117 per mile. The EV is about 2.7 times cheaper.

Frequently Asked Questions

How long does it take to charge an electric car at home?
On a typical 7.4 kW Level 2 charger, a 60 kWh battery from 20% to 80% takes about 4.9 hours. On a standard 120 V outlet (1.2 kW), the same charge would take about 30 hours, which is impractical for daily use. Most owners install a Level 2 charger for overnight charging.

Why does my car charge slower than the calculator says?
Because the calculator assumes constant power. In reality, charging speed tapers above 80% and can be reduced by cold weather, battery temperature, and the car’s onboard charger limit. Also, AC charging has energy losses of 5–15%, so the wall power draw is higher than the battery receives.

How much does it cost to fully charge an electric car?
Multiply your battery capacity (usable kWh) by your electricity rate. For a 60 kWh battery at $0.15/kWh, a full charge from empty costs $9.00. If you charge from 20% to 80%, it costs $5.40. Use the calculator with your specific numbers.

Is it cheaper to charge at home or at a public station?
Home charging is almost always cheaper, especially with time-of-use rates. Public Level 2 chargers often cost $0.25–$0.40 per kWh, and DC fast chargers can be $0.40–$0.60 per kWh. The calculator shows the difference: for a 36 kWh charge, $0.15/kWh vs. $0.50/kWh means $5.40 vs. $18.00.

Should I charge to 100% every night?
For daily driving, most manufacturers recommend charging to 80–90% to reduce battery wear. Charging to 100% is fine for road trips, but avoid leaving the car at 100% for long periods, especially in hot weather. The calculator can show you the time difference: charging from 20% to 80% on a 7.4 kW charger takes 4.9 hours, while 20% to 100% takes 6.5 hours.

What does “kWh” mean for an electric car?
It’s a unit of energy. Think of it like gallons of fuel. A 60 kWh battery holds 60 kilowatt-hours of energy. One kWh is the energy used by a 1,000-watt appliance running for one hour. Your electricity bill charges you per kWh.

Safety and Accuracy Notes

This calculator is for educational estimation. Always follow your vehicle manufacturer’s charging recommendations and your local electrical codes. For home charger installation, consult a licensed electrician to ensure your circuit can handle the load. Never exceed the charger’s rated capacity. The formula assumes ideal conditions; real-world results vary. For precise cost, use your actual electricity bill rate and account for losses.

Formula used

in batt | Battery capacity | kWh | 60 | 1 | 200
in start | Starting charge | % | 20 | 0 | 100
in target | Target charge | % | 80 | 0 | 100
in power | Charger power | kW | 7.4 | 0.5 | 350
in rate | Electricity rate | $/kWh | 0.15 | 0.01 | 1
out hours | Charging time | h | (batt * (target - start) / 100) / power | 2
out energy | Energy needed | kWh | batt * (target - start) / 100 | 1
out cost | Cost | $ | batt * (target - start) / 100 * rate | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.