Electric Vehicle (EV) Charging Time & Cost Estimator

Why you pay for more energy than actually reaches the battery

Charging 42 kWh into the battery pack using a 7.2 kW charger at 90% efficiency takes 6.48 hours and pulls 46.67 kWh from the wall -- notably more than the 42 kWh that actually reaches the battery, at a cost of $7.47.

That gap between wall kWh (46.67) and pack kWh (42) is exactly what the 90% efficiency figure describes -- some energy is lost as heat during the AC-to-DC conversion process inherent to charging, so you're always billed for more energy than the battery actually stores, which is why 'wall kWh, not pack kWh' is the number that determines your actual electricity cost.

Charging time (6.48 hours) is calculated from the pack kWh needed divided by the effective charging rate (kW x efficiency): 42 / (7.2 x 0.90) = 42 / 6.48 = 6.48 hours -- the efficiency loss doesn't just affect cost, it also means the charger takes measurably longer to deliver a given amount of usable battery energy than a naive kWh-divided-by-kW calculation would suggest.

Why efficiency and rate both matter for real charging time

Hours = kWh / (kW x efficiency). You pay for wall kWh, not pack kWh. Charging efficiency (90% here) varies by charging speed, temperature, and the specific vehicle and charger combination -- Level 2 home charging and DC fast charging often have somewhat different efficiency characteristics, so 90% is a reasonable planning estimate rather than a universal constant across every charging scenario.

The 7.2 kW charger rate is the bottleneck in this calculation -- a higher-power charger (like a DC fast charger rated well above 7.2 kW) would proportionally reduce charging time for the same kWh need, though very high charging rates can also somewhat change the efficiency percentage compared to a slower, steadier charge.

This models charging from empty to the specified kWh need in one continuous session at a constant rate -- in reality, many EVs taper charging speed as the battery approaches full, which this simplified constant-rate model doesn't capture for the final portion of a charge.

Related EV and energy-cost tools

For comparing this electric charging cost against a gas-powered vehicle's fuel cost for the same trip, the Fuel Cost & Trip Distance Calculator uses the same per-mile cost framing for gasoline.

For a related household energy-cost calculation using the same rate-times-usage logic, the Electric Bill / Appliance Wattage Calculator applies similar math to a specific appliance.

Frequently Asked Questions (FAQ)