How long a charge takes
Charging time comes down to how much energy you need to add and how fast the charger delivers it. The energy is the battery size times the percentage you are adding; the time is that energy divided by the charger's power, with a small adjustment for losses. Charging is not perfectly efficient — some energy becomes heat in the onboard charger and the cells — so the amount drawn from the wall is a bit more than what lands in the battery, typically about 10% more on AC.
AC versus DC, and why the model is honest for one but not the other
For AC charging — a home Level 1 or Level 2 station up to 22 kW — the car draws steady power the whole time, so the simple "energy ÷ power" calculation is accurate. DC fast charging is different: the car pulls big power when the battery is low, then tapers sharply as it fills, because pushing high current into a nearly full lithium battery would damage it. That is why fast chargers are rated for the 10–80% window and why the last 20% can take almost as long as the first 70%. This calculator's linear estimate is a reliable number for AC and a lower bound for DC — when you pick a fast-charger power, it says so.
What it costs, and versus gasoline
Cost is simply the energy drawn from the wall times your electricity rate. A 75 kWh battery charged from 20% to 80% adds 45 kWh, draws about 50 kWh from the wall, and at 15¢/kWh costs $7.50 — for roughly 200 miles of range. Per mile — counting those charging losses, since the dash's mi/kWh figure is battery-side but you pay for wall energy — that is about 4.8¢ (15¢ ÷ 3.5 mi/kWh ÷ 0.90). A 30 mpg gasoline car at $3.50/gallon costs 11.7¢/mile, well over twice as much. Public DC fast charging is priced higher than home electricity, which narrows the gap, so home Level 2 charging is where an EV's running-cost advantage really lives.
Related tools: the battery pack builder for pack internals, the unit converter for mi/km and other conversions, and the solar calculator if you charge from your own panels.