EV Charging Calculator

Charging is two questions that share one number. How much energy has to move, and how fast can it move?

The energy is the easy part: your usable battery capacity multiplied by the percentage gap you are closing. A 75 kWh car going from 20% to 80% needs 45 kWh in the battery.

But you always pay for more than the battery receives. Converting AC from your wall into DC in the battery loses about 10%, so 45 kWh in the pack means 50 kWh off your meter — and it is the meter that bills you. DC fast chargers do the conversion in the station and lose less, about 5%.

Time depends on where the charger's rating is measured. Level 1 and Level 2 chargers are rated by what they pull from the wall, so charge time uses the grid figure. DC chargers are rated by what they push into the battery, so time uses the battery figure.

1. Step 1 Energy into the battery battery_kWh = capacity × (target% − current%) ÷ 100
2. Step 2 Energy off your meter grid_kWh = battery_kWh ÷ efficiency Efficiency is 0.90 for AC charging, 0.95 for DC fast charging.
3. Step 3 Charging time hours = grid_kWh ÷ charger_kW (AC) or battery_kWh ÷ charger_kW (DC)
4. Step 4 What it costs cost = grid_kWh × your price per kWh
5. Step 5 Cost per 100 miles (100 ÷ miles_per_kWh ÷ efficiency) × price_per_kWh The gas comparison is (100 ÷ MPG) × price per gallon.

Example: a 75 kWh car from 20% to 80% needs 45 kWh in the battery and 50 kWh from the grid. On a 7.4 kW Level 2 charger that is 6 hours 45 minutes, and at $0.17/kWh it costs $8.50 for about 158 miles of range.

Charging is two questions that share one number. How much energy has to move, and how fast can it move?

The energy is the easy part: your usable battery capacity multiplied by the percentage gap you are closing. A 58 kWh car going from 20% to 80% needs 34.8 kWh in the battery.

But you always pay for more than the battery receives. Converting AC from your wallbox into DC in the battery loses about 10%, so 34.8 kWh in the pack means 38.7 kWh off your meter — and it is the meter that bills you. DC rapid chargers do the conversion in the station and lose less, about 5%.

Time depends on where the charger's rating is measured. A wallbox is rated by what it draws from the supply, so charge time uses the grid figure. DC rapid chargers are rated by what they push into the battery, so time uses the battery figure.

1. Step 1 Energy into the battery battery_kWh = capacity × (target% − current%) ÷ 100
2. Step 2 Energy off your meter grid_kWh = battery_kWh ÷ efficiency Efficiency is 0.90 for AC charging, 0.95 for DC rapid charging.
3. Step 3 Charging time hours = grid_kWh ÷ charger_kW (AC wallbox) or battery_kWh ÷ charger_kW (DC)
4. Step 4 What it costs cost = grid_kWh × your price per kWh
5. Step 5 Cost per 100 km (kWh_per_100km ÷ efficiency) × price_per_kWh The petrol comparison is litres_per_100km × price per litre. Divide by 100 for cost per kilometre.
6. Step 6 Charging speed km_per_hour = range_added ÷ hours This is the number that actually separates a household socket from a wallbox — about 12 km/h against 40.
7. Step 7 What a year costs annual_cost = cost_per_100km × km_per_year ÷ 100 Run the same sum with the petrol figures and the difference is your yearly saving.

Example: a 58 kWh ID.3 from 20% to 80% needs 34.8 kWh in the battery and 38.7 kWh from the grid. On a 7.4 kW wallbox that is 5 hours 14 minutes, and at €0.28/kWh it costs €10.83 for about 193 km of range — roughly 37 km of range per hour on the charger, at 5.6 cents a kilometre.

• Charging is modeled at a constant rate. This is accurate for Level 1 and Level 2 charging, where the onboard charger is the bottleneck the whole way. It is optimistic for DC fast charging, which tapers steeply above roughly 60–80% state of charge.
• Charging efficiency is 90% for AC and 95% for DC. Cold batteries do worse, sometimes much worse, because the car spends energy heating the pack before it can accept a charge.
• Battery capacities are usable capacity, not gross pack size. Manufacturers reserve a buffer at both ends that you never see.
• AC charger power is the rate drawn from the grid; DC charger power is the rate delivered to the battery. This is why the time formula differs between the two.
• The station rating is treated as the actual delivered rate. In practice your car's own maximum, the number of cars sharing the station and the battery temperature all cap it lower.
• No idle, connection or session fees are included, and no time-of-use rate changes mid-session. Public networks often add both.
• The gas comparison uses fuel and electricity only. It ignores maintenance, which usually favors the EV, and depreciation, insurance and taxes, which vary far too much to model.
• Miles per kWh is taken from your trip computer, which already accounts for your driving. Highway speeds and cold weather can knock 30% off it.

• Charging is modelled at a constant rate. This is accurate for AC wallbox charging, where the onboard charger is the bottleneck the whole way. It is optimistic for DC rapid charging, which tapers steeply above roughly 60–80% state of charge.
• Charging efficiency is 90% for AC and 95% for DC. Cold batteries do worse, sometimes much worse, because the car spends energy heating the pack before it can accept a charge.
• Battery capacities are usable capacity, not gross pack size. Manufacturers reserve a buffer at both ends that you never see.
• Wallbox power is the rate drawn from the supply; DC charger power is the rate delivered to the battery. This is why the time formula differs between the two.
• A three-phase 11 kW or 22 kW wallbox only helps if your car's onboard charger accepts it. Most European EVs cap at 11 kW, and several are single-phase 7.4 kW only.
• The station rating is treated as the actual delivered rate. In practice your car's own maximum, the number of cars sharing the station and the battery temperature all cap it lower.
• No idle fees, connection fees or subscription costs are included, and no time-of-use tariff changes mid-session. European rapid networks frequently add all three.
• Electricity prices vary enormously across Europe — from roughly €0.10/kWh in Hungary to over €0.40 in Germany and Ireland. The €0.28 default is a rough EU household average including taxes; use your own bill.
• The petrol comparison uses fuel and electricity only. It ignores maintenance, which usually favours the EV, and depreciation, insurance, road tax and any congestion or emissions-zone charges.
• Consumption in kWh/100 km comes from your trip computer, which already reflects your driving. Motorway speeds and winter can add 30% or more.
• Charging speed is the average across the whole session, not the peak. On DC rapid charging the real rate is much higher at the start and much lower at the end.
• The yearly comparison assumes every kilometre is charged at the rate you entered. In practice most drivers do 80–90% of their charging at home and the rest at public prices, so the true figure sits a little above the home-only number.
• The public charging rate used in the home-versus-public comparison is a mid-range European rapid rate. Networks charge anywhere from €0.35 to €0.89 per kWh depending on country and subscription.