EV charging cost calculator
Charging is not perfectly efficient — you pay for more energy than reaches the battery. This counts that loss so the number matches your bill.
The loss nobody includes
Some of the electricity drawn from the wall becomes heat in the cable, the onboard charger and the battery itself rather than stored charge. Level 2 home charging typically lands around 85 to 90 percent efficient, so a 60 kilowatt-hour top-up actually pulls closer to 67 from the meter. Most online estimates skip this entirely, which is why they read low against a real electricity bill.
The 20 to 80 percent default reflects how people actually charge. Batteries charge more slowly at the top of their range and spend less time at high state of charge if you stop at 80, which is the routine most manufacturers recommend for daily use — full charges are for road trip days.
Add your miles per kilowatt-hour and the cost-per-mile line becomes the number worth carrying around, because it is directly comparable to a petrol car's cost per mile. It is also the figure that makes home charging's advantage obvious: public rapid charging often costs several times the home rate for the same energy.
Questions
What efficiency should I use?
Around 90 percent for a Level 2 home charger. Slow charging on a standard household socket is less efficient, often nearer 80, because the overheads run for far longer.
Why charge only to 80 percent?
Charging slows considerably above 80, and most manufacturers suggest keeping daily charging below full to reduce battery ageing. Charge to 100 when you actually need the range.
Does this work for public charging?
Enter the public price per kilowatt-hour and set efficiency near 95 percent, since DC rapid charging bypasses the onboard charger. Note many networks bill by the minute instead, which this does not model.