Suppose a 64 kWh usable battery rises from 20% to 95%. The battery gain is 64 × 0.75 = 48 kWh. With 90% charging efficiency, meter energy is 48 ÷ 0.90 = 53.33 kWh. At $0.28/kWh, multiply 53.33 by 0.28 for $14.93. The EV charging cost calculator performs this sequence with editable capacity, percentage, tariff, and efficiency.
Worked example with numbers
Use the rate shown on the bill for the time and tariff that actually apply. A flat rate is simple; a time-of-use tariff requires the rate for the charging interval. For a monthly estimate, sum the meter energy of each session instead of multiplying battery capacity by the number of charges. A car that normally charges from 45% to 75% does not receive a full battery each night.
How to make the calculation
Separate three energy terms in notes: usable battery energy in kWh, energy delivered by the charging equipment, and grid energy recorded by the meter. The battery percentage gives stored energy; it does not report wall energy. If a vehicle app reports 40 kWh added and the utility interval meter records 44 kWh, the difference can include conversion losses and equipment standby use.
Check the units and assumptions
Do not multiply 64 kWh by the tariff when only 48 kWh was added. Do not treat a percentage point as a kWh value without battery capacity. Another frequent error is entering cents as dollars: 28 cents/kWh is $0.28/kWh, not $28/kWh. Check the currency and whether tax or fixed charges are already included in the stated rate.
Common mistakes
This calculation estimates variable electricity energy cost. It does not determine an electrician’s work, equipment installation, demand charges, public-station session fees, or the exact loss rate in cold weather. A vehicle may reserve battery capacity outside the displayed range, so use the manufacturer’s usable-capacity figure when the goal is accuracy.
When this result does not apply
The U.S. Department of Energy Alternative Fuels Data Center states that EV cost per mile depends on electricity price and vehicle efficiency, and gives a worked 54 kWh, 200-mile example in its home charging guide. It also notes that time of use can change residential cost.
Source for the external fact
Compare household and public scenarios with the home-versus-public charger tool, and use the appliance energy calculator for other kWh-based household loads.
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