Complete guide
Reviewed July 2026The cost of charging an electric vehicle depends on just three things: how much energy goes into the battery, how much is lost on the way in, and what you pay per kilowatt-hour. Yet real-world answers vary enormously — home charging can cost a third of DC fast charging for the same kilometres.
This calculator computes the true cost of any charge session: enter your battery capacity, current and target charge levels, charging efficiency and electricity price, and it returns the energy drawn from the grid, the session cost, the full 0–100% cost and the cost per percentage point.
Crucially, it accounts for charging losses — the 8–15% of grid energy that becomes heat in the charger and battery rather than usable range. Calculators that skip losses understate your real cost on every session.
How EV charging cost is calculated
Energy drawn (kWh) = Battery capacity × (Target % − Current %) ÷ 100 ÷ Efficiency Charging cost = Energy drawn × Price per kWh
The battery stores the net energy, but your meter records the gross energy — everything the charger pulled from the grid, including conversion and thermal losses. Efficiency captures the ratio between the two.
Typical charging efficiency
AC charging routes power through your car's onboard charger, which converts AC to DC with some loss. DC fast chargers do the conversion in the station with bigger, more efficient hardware — but you pay a much higher per-kWh price for the speed.
| Charging method | Typical efficiency | Where losses go |
|---|---|---|
| AC slow (3-pin, 2–3 kW) | 80–88% | Onboard charger, long session heat |
| AC wallbox (7–11 kW) | 88–92% | Onboard charger conversion |
| DC fast (50–150 kW) | 90–94% | Station converts AC→DC; battery cooling |
Worked example
- Car: 40 kWh battery, charging from 20% to 80% at home, 90% efficiency, tariff ₹8/kWh.
- Energy added to battery = 40 × (80 − 20)/100 = 24 kWh.
- Energy drawn from grid = 24 ÷ 0.90 = 26.7 kWh.
- Session cost = 26.7 × 8 = ₹213.
- If the car uses 150 Wh/km, that 60% charge delivers about 160 km — roughly ₹1.33 per km, versus ₹6–7 per km for a comparable petrol car at ₹105/litre and 16 km/l.
Home vs public vs DC fast charging
The pattern holds worldwide: home charging at domestic rates is the floor, DC fast charging costs 2–3× more, and dedicated EV/night tariffs (offered by a growing number of utilities) cut home costs another 25–40%. Drivers who do 90% of charging at home and reserve DC for road trips get most of the EV savings.
| Location | Typical price | Full-charge cost | Cost per km (150 Wh/km) |
|---|---|---|---|
| Home (domestic tariff) | ₹6–9/kWh | ₹267–400 | ₹1.0–1.5 |
| Home (EV night tariff) | ₹4–6/kWh | ₹178–267 | ₹0.7–1.0 |
| Public AC charger | ₹12–18/kWh | ₹533–800 | ₹2.0–3.0 |
| DC fast charger | ₹18–25/kWh | ₹800–1,111 | ₹3.0–4.2 |
How to use this calculator
- Enter your battery's usable capacity in kWh (check the spec sheet — usable is sometimes 2–4 kWh below gross).
- Set the current and target charge percentages for the session you're planning.
- Pick a charging efficiency: 90% is a sound default for a home wallbox; use 85% for a portable 3-pin charger, 92% for DC fast charging.
- Enter your electricity price per kWh — from your utility bill for home charging, or the displayed rate at a public station.
- Read the session cost, grid energy, full-charge cost and cost per 1% — handy for comparing stations that bill by the minute.
What drives your real-world cost
- Tariff structure — time-of-use plans can make midnight charging half the price of evening charging.
- Efficiency of your charger — a quality 7 kW wallbox typically beats a trickle charger by 5–8 points, which compounds over years.
- Temperature — cold batteries accept charge less efficiently and may spend energy on heating; winter sessions cost more per km.
- Idle fees — many DC networks bill per minute after charging completes; always move the car promptly.
- Subscription plans — frequent DC users often save 15–30% with network memberships.
Common mistakes
- Using gross battery capacity instead of usable capacity — overstates energy and cost.
- Ignoring losses — the 24 kWh your battery gained cost you ~27 kWh at the meter.
- Comparing EV cost per km against petrol without including home-charger installation amortisation, if you're doing a full ownership comparison.
- Assuming DC charging speed is constant — the taper above 80% means the last 20% can take as long as the previous 40%.
Frequently asked questions
Glossary
- kWh
- Kilowatt-hour — the unit of electrical energy; EV batteries and electricity bills both use it.
- Charging efficiency
- Battery energy gained ÷ grid energy consumed; typically 85–94% depending on the charger.
- Usable capacity
- The portion of a battery's gross capacity the car allows you to cycle, protecting cell longevity.
- Onboard charger
- The car's internal AC→DC converter; its rating (e.g., 7.4 kW) caps AC charging speed.
- DC fast charging
- High-power charging where the station supplies DC directly to the battery, bypassing the onboard charger.
- Charging curve / taper
- The reduction in charging power as the battery fills, steepest above ~80%.
- Time-of-use tariff
- An electricity plan with cheaper off-peak rates, ideal for scheduled overnight EV charging.
- Wh/km
- Watt-hours per kilometre — an EV's energy consumption rate; 130–180 is typical for compact EVs.
- Idle fee
- Per-minute charge some networks apply after a session ends to keep bays available.
Key takeaways
EV charging cost is simple physics: energy added ÷ efficiency × price. The big levers are where you charge (home beats DC fast by 2–3×), when you charge (night tariffs cut 25–40%), and honest accounting for the ~10% losses most calculators ignore. Master those and a typical EV runs at a fifth of petrol cost per kilometre.
Enter your battery size, charge window and tariff above to see your true session cost — then compare it against a DC fast-charge price to see what home charging saves you.