Quick Answer

Charging a 75 kWh battery from 20% to 80% at $0.13/kWh with 90% charging efficiency draws approximately 50.0 kWh from the wall, costing approximately $6.50.

Battery Capacity (kWh)

Current Charge (%)

Target Charge (%)

Electricity Rate ($/kWh)

Charging Efficiency (%)

Compare with gas vehicle (optional)

Gas Price ($/gal)

Gas Vehicle MPG

EV Range (miles, full charge)

Common Examples

Input	Result
75 kWh battery, 20% to 80%, $0.13/kWh, 90% efficiency	Estimated 50.0 kWh, $6.50
60 kWh battery, 10% to 100%, $0.15/kWh, 90% efficiency	Estimated 60.0 kWh, $9.00
100 kWh battery, 5% to 90%, $0.12/kWh, 88% efficiency	Estimated 96.6 kWh, $11.59
40 kWh battery, 30% to 80%, $0.14/kWh, 90% efficiency	Estimated 22.2 kWh, $3.11
82 kWh battery, 15% to 95%, $0.11/kWh, 90% efficiency	Estimated 72.9 kWh, $8.02

How It Works

The Formula

EV charging cost accounts for the energy needed to fill the battery and the efficiency loss during charging:

Battery kWh Needed = Battery Capacity x (Target % - Current %) / 100

Wall kWh Needed = Battery kWh Needed / (Charging Efficiency / 100)

Cost = Wall kWh Needed x Electricity Rate

Where:

• Battery Capacity = the total energy storage of the EV battery in kilowatt-hours (kWh)
• Charging Efficiency = the percentage of energy from the wall that actually reaches the battery (typically 85% to 95%)
• Electricity Rate = cost per kilowatt-hour from your utility bill

Charging Efficiency Explained

Not all electricity drawn from the outlet reaches the battery. Some energy is lost as heat in the charger, cables, and battery management system. Level 1 (120V) chargers are typically 80% to 85% efficient. Level 2 (240V) chargers are typically 88% to 92% efficient. DC fast chargers are approximately 90% to 95% efficient at the charger level, though they can generate more heat in the battery.

Equivalent MPG (MPGe)

The EPA uses MPGe (miles per gallon equivalent) to compare EVs with gas vehicles. The calculation converts electricity cost per mile to an equivalent fuel economy: MPGe = Gas Price / EV Cost per Mile. An EV with a low cost per mile translates to a high MPGe, often 100 to 140 MPGe for modern electric vehicles.

Home vs. Public Charging Costs

Home electricity rates in the United States average approximately $0.12 to $0.16 per kWh. Public Level 2 chargers may cost $0.20 to $0.35 per kWh. DC fast chargers at public stations can cost $0.30 to $0.60 per kWh or charge per-minute fees. Charging at home during off-peak hours is typically the least expensive option.

Worked Example

For a 75 kWh battery charged from 20% to 80% at $0.13/kWh with 90% efficiency: Battery kWh needed = 75 x (80 - 20) / 100 = 75 x 0.60 = 45 kWh. Wall kWh needed = 45 / 0.90 = 50.0 kWh. Cost = 50.0 x $0.13 = $6.50. If comparing to a 25 MPG gas vehicle at $3.50/gallon with 300-mile EV range: Miles per kWh = 300 / 75 = 4.0. EV cost per mile = $0.13 / (4.0 x 0.90) = $0.036. Equivalent MPGe = $3.50 / $0.036 = 97.2 MPGe. Miles added = 45 x 4.0 = 180 miles. Gas cost for 180 miles = (180 / 25) x $3.50 = $25.20. Savings = $25.20 - $6.50 = $18.70.

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Frequently Asked Questions

What is a typical electricity rate for EV charging?

In the United States, residential electricity rates average approximately $0.12 to $0.16 per kWh. Rates vary significantly by state and utility. Some utilities offer special EV or time-of-use rates that can be as low as $0.05 to $0.08 per kWh during off-peak hours (typically overnight).

Why should I not always charge to 100%?

Most EV manufacturers recommend daily charging to 80% to preserve battery health over time. Charging above 80% slows significantly and generates more heat, which can degrade the battery faster. Charging to 100% is fine for long trips but is not ideal for daily use.

What is charging efficiency and why does it matter?

Charging efficiency is the ratio of energy stored in the battery to energy drawn from the electrical source. A 90% efficiency means 10% of the electricity is lost as heat during charging. This affects cost because the actual electricity consumed from the wall is higher than the energy stored in the battery.

How does DC fast charging compare in cost to home charging?

DC fast charging is typically 2 to 4 times more expensive per kWh than home charging. Public fast chargers often charge $0.30 to $0.60 per kWh or per-minute fees. The convenience premium makes fast charging comparable to gas costs in some cases, while home charging remains significantly cheaper.

How much does it cost to charge an EV per month?

Monthly charging cost depends on driving distance and electricity rate. At the U.S. average of 1,000 miles per month, a vehicle getting 3.5 miles per kWh at $0.13/kWh costs approximately $37 per month for electricity, compared to approximately $140 per month for a 25 MPG gas vehicle at $3.50/gallon.