How to Calculate EV Charging Time and Cost

• Usable battery capacity (kWh) — from the manufacturer. It is often lower than the gross capacity.
• Starting and target state of charge (%) — where the battery is now and where you will stop.
• Charger power (kW) — the rating of the home charger or public charger.
• The car's maximum charging power — a separate AC limit (its onboard charger) and DC limit.
• Charging losses — the share of energy drawn that does not end up stored in the battery.
• Price — your home unit rate, or the public network's per-kWh, per-minute, session and idle fees.

The Electric Vehicles hub collects the related tools and guides.

Energy into battery (kWh) = Usable capacity × (Target % − Start %) ÷ 100 Energy drawn (kWh) = Energy into battery ÷ Charging efficiency

Illustrative: 75 kWh usable, 20% → 80%, charging efficiency 90% Energy into battery: 75 × 0.60 = 45 kWh Energy drawn: 45 ÷ 0.90 = 50 kWh

Charging efficiency is not a fixed number. It depends on the car, the charging power, battery temperature and whether the car is heating or cooling its battery while it charges. To find your own, compare the kWh your home charger or a dedicated meter recorded with the kWh the car reports added over the same sessions. Otherwise treat it as an assumption and try a range.

Charging power is the lowest of three limits:

• The supply or charger — a home charger's setting, or a public charger's maximum (which some sites share between connectors).
• The car — on AC, the onboard charger converts AC to DC and has its own maximum; on DC, the car's maximum DC power applies.
• The battery's state — state of charge and temperature, mainly on DC.

For single-phase AC, power = voltage × current: 230 V × 32 A = 7.36 kW. For three-phase AC on a nominal 400/230 V supply, you can describe the same system two ways:

• Per phase, using the phase-to-neutral voltage: 3 × 230 V × 16 A ≈ 11.0 kW
• Using the line-to-line voltage: √3 × 400 V × 16 A ≈ 11.1 kW

Both describe the same nominal system — 400 V is √3 × 230 V, so the difference is only rounding of the nominal voltages. These nominal figures do not guarantee the power the car actually receives; the onboard charger, the supply and the conditions set the real figure. A car with a 7.4 kW onboard charger plugged into a 22 kW public AC charger still charges at no more than 7.4 kW.

Whether your home supply suits a given charger power is a separate question — see the Home Charger Sizing Tool. Installation work belongs to a qualified electrician.

On AC, power is usually close to constant for most of the session, so dividing energy by power is a reasonable first estimate. Treat it as the ideal case: power can drop near a full battery and in cold weather.

On DC, power changes throughout the session. It is usually highest at low state of charge and falls as the battery fills (tapering), so the charger's maximum rating is not the average power you get, and energy ÷ charger rating underestimates the time. The last part of the battery generally charges much more slowly than the first, which is why many manufacturers quote DC times for a window such as 10% → 80%.

Use the manufacturer's stated time for a window and the energy that window adds:

Average power (kW) = Energy into battery ÷ Time (h)

Illustrative: a stated 10% → 80% of 75 kWh (52.5 kWh) in 30 minutes means an average of 52.5 ÷ 0.5 = 105 kW over that window — even on a charger rated higher.

Other things that change real DC sessions:

• Battery temperature — a cold battery accepts less power until it warms. Many cars can precondition the battery when you navigate to a fast charger; your manual explains whether yours does.
• Start percentage — arriving at a lower state of charge usually gives a higher average.
• Site power sharing — some sites split power between cars.

Range added per hour (km) = Charging power (kW) × Charging efficiency ÷ Consumption (kWh/100 km) × 100

Illustrative: 11 kW × 0.90 ÷ 17 kWh/100 km × 100 ≈ 58 km per hour of AC charging. If your consumption is in Wh/mi, convert it with the Wh/mi to Wh/km converter (1 kWh/100 km = 10 Wh/km). Use your own trip-computer average; consumption changes with speed, temperature and driving.

• At home, you pay for the energy drawn through your meter, which includes the charging losses in the car.
• On public chargers, you pay for the energy the charger meters (where pricing is per kWh), plus any fees. On AC the car's onboard charger is on your side of the meter, so its losses are in the metered kWh. On DC the conversion happens in the charger, so the metered energy is closer to — but usually still above — what the battery stores.

In every case, use the kWh the tariff or network actually bills, not the kWh added to the battery.

Networks price sessions in different ways, sometimes combined:

• Per kWh — easiest to compare with a home rate.
• Per minute — the cost per kWh then depends on how fast the car actually charges.
• Session or connection fee — a fixed amount per session.
• Idle or overstay fees — charges for staying connected after charging ends or beyond a time limit.
• Membership — a monthly fee that lowers the per-kWh price (how that spreads across a month belongs in the EV monthly charging cost guide).

Prices vary by network, country, location, charger speed and time, and change often. Check the price shown on the charger or app before you start; this guide uses no real network prices.

Every price below is an invented round number to show the arithmetic, not a market price. The DC metered energy (55 kWh for 52.5 kWh into the battery) is also illustrative.

• The time formula assumes constant power. On DC it is a lower bound; use the car's charging curve or the manufacturer's stated window.
• Charging efficiency is an assumption unless you measure it.
• Battery heating, cabin preconditioning and the car's electronics can draw energy during a session, especially in cold weather.
• Tariffs and network prices change; recheck them rather than reusing an old figure.

The EV Charging Cost Calculator runs Steps 1–4: enter battery size, start and target charge, charger power, charging efficiency and prices to get session energy, time and cost. Its time estimate uses the constant-power formula, so for DC treat it as a lower bound. The methodology page documents the formulas.

Next questions belong to other guides:

• What does charging cost me per month? — EV monthly charging cost guide.
• What charger power do I need at home? — Home Charger Sizing Tool.
• How does an EV's running cost compare with a petrol car? — EV vs petrol running cost comparison.