The formula, with the part most calculators skip
Charging an EV is not just battery size × electricity price. Some of what the wall meter records never reaches the battery, it is lost as heat in the onboard charger, the cable and the battery management system. The honest formula grosses the battery energy up to wall energy first:
wall energy = battery kWh ÷ (1 − losses), then cost = wall energy × price per kWh
Typical losses: about 10% for AC home charging (conversion happens in the car) and about 5% for DC fast charging (conversion happens in the station). Skip this step and every estimate runs 5–10% low, small per charge, real over a year.
Worked example
A 60 kWh battery charged at home at ₹8/kWh with 10% losses: wall energy = 60 ÷ 0.9 = 66.7 kWh, so a full charge costs about ₹533. If the car consumes 15 kWh/100 km, then 1,000 km of driving needs 150 kWh in the battery, about 166.7 kWh from the wall, costing roughly ₹1,333, or ₹1.33/km.
Home vs public charging: the 2–3× gap
Domestic electricity is one price; public DC fast charging is another economy entirely. Networks pay commercial tariffs, finance expensive hardware and charge for convenience, per-kWh rates of 2–3× the home rate are normal. The same 60 kWh charge that costs ₹533 at home can cost ₹1,100–1,600 at a highway fast charger.
| Charging scenario | Typical loss | Typical price | 60 kWh full charge |
|---|---|---|---|
| Home AC, off-peak tariff | ~10% | ₹6/kWh | ~₹400 |
| Home AC, standard tariff | ~10% | ₹8/kWh | ~₹533 |
| Public DC fast charger | ~5% | ₹18–24/kWh | ~₹1,140–1,520 |
The practical takeaway: an EV's famous running-cost advantage assumes mostly-home charging. If your situation forces mostly public fast charging, run the numbers before assuming the savings, the calculator handles both cases, just change the price and the loss figure.
Time-of-day tariffs: free savings for night owls
Where your electricity board offers time-of-day pricing, overnight rates are discounted, and overnight is when a home-charged EV sits plugged in anyway. Set the car (or wall box) to start charging in the off-peak window and your effective rate drops with no behaviour change at all. Enter the off-peak rate in the calculator to see your real cost; the difference versus the standard tariff, compounded over a year of driving, often covers the cost of the wall box.
What moves your per-km cost
- Consumption (kWh/100 km): the biggest factor. City driving with regeneration can beat the spec figure; sustained highway speeds can exceed it by 20–30%.
- Electricity price: linear, halve the tariff, halve the cost. Off-peak plans and solar change this dramatically.
- Charger type: AC vs DC changes the loss factor; where you charge changes the price far more.
- Climate: heating and cooling draw from the same battery. Expect worse winter numbers.
Comparing against a petrol car
Per-km cost is the number that makes the EV-vs-petrol comparison honest. Once you have yours, put it side by side with a petrol car's using the EV vs petrol cost calculator, for most home-charging setups the gap is dramatic. If you are costing a specific petrol trip instead, the fuel cost calculator does the same per-km arithmetic for litres and mileage.