EV Charging Calculator Methodology

1. Battery energy added

Battery energy added is usable battery capacity multiplied by the change in state of charge. A 60 kWh usable battery moving from 20 percent to 80 percent adds 36 kWh because the session adds 60 percent of the usable capacity.

Usable capacity is preferred to gross or nameplate capacity because the vehicle normally reserves upper and lower buffers that are not available to the driver. Where model pages quote a battery figure, the assumed variant and source are identified so readers can check whether their trim differs.

2. Wall energy and charging efficiency

The utility meter records energy drawn from the grid, not only energy stored in the battery. Charging losses occur in cables, AC-to-DC conversion, battery resistance, cooling or heating systems and vehicle electronics that remain active during the session.

Wall energy is therefore estimated by dividing battery energy by charging efficiency expressed as a decimal. At 90 percent efficiency, storing 36 kWh requires about 40 kWh from the wall. Users can replace the default efficiency with a measured value from their own charger or meter.

3. Charging-session cost

Session cost equals wall energy multiplied by the electricity price per kWh. With 40 kWh drawn from the wall at 0.30 per kWh, the energy portion of the session costs 12.00.

The price field should use the marginal energy rate that applies while charging. Standing charges, monthly subscriptions, connection fees, parking fees and idle fees are not automatically distributed across a session because those charges depend on the user's contract or behaviour rather than on energy consumed.

4. Cost per 100 km and cost per mile

Driving cost starts with vehicle energy consumption. For cost per 100 km, vehicle consumption in kWh per 100 km is divided by charging efficiency and multiplied by the electricity price. A vehicle using 17 kWh per 100 km at 90 percent efficiency requires about 18.9 kWh from the wall per 100 km.

Cost per mile applies the same principle using energy per mile. If a source gives miles per kWh, the reciprocal converts it to kWh per mile. When comparing vehicles, use consumption from similar driving conditions rather than mixing optimistic laboratory values with real-world averages.

5. AC charging time

For AC charging, ideal time is wall energy divided by usable charging power. Usable power is the lowest applicable limit among the electrical supply, charge point, cable and vehicle onboard charger. A car that accepts 11 kW AC will not charge at 22 kW from a 22 kW post.

This method is reasonably useful for home charging because AC power is comparatively steady through most of a session. Real time can still be longer because of balancing, thermal control, battery preconditioning and the final high-state-of-charge phase.

6. DC fast-charging time

DC fast charging cannot be estimated accurately by dividing energy by the charger peak rating. Vehicle charging power changes with state of charge and battery temperature, and the highest advertised rate may be held only briefly.

Where a manufacturer publishes a 10-to-80-percent charging time for the specified battery and conditions, that figure is more useful than theoretical peak-power arithmetic. Model pages therefore distinguish peak kW from actual session time and note that battery preconditioning and charger capability can materially change the result.

7. Electricity-price references

Country pages use residential electricity-price references from identifiable authorities or utilities such as Eurostat, Ofgem and the U.S. Energy Information Administration where applicable. The reporting period is shown beside the figure because a national average is a comparison benchmark rather than a quote for a specific household.

Users should replace the country reference with the price on their own tariff for personal budgeting, particularly when a time-of-use or dedicated EV tariff applies. The site does not convert currencies inside a country figure; each reference remains labelled in its source currency.

8. Rounding and interpretation

Intermediate calculations are kept at higher precision and display values are rounded for readability. Small differences between a displayed example and a hand calculation can therefore result from rounding rather than from a different formula.

Calculator output is an estimate for the inputs supplied. It should not be treated as a guaranteed electricity bill, laboratory efficiency measurement or charging-network quote. Temperature, tyre pressure, speed, battery conditioning, charger metering and tariff rules can all change a real result.

9. What the calculators deliberately exclude

The core calculators do not automatically model depreciation, finance, insurance, servicing, battery degradation, demand charges, solar export opportunity cost or every public-network fee. Adding those items would require assumptions that differ greatly between users and would make the result appear more precise than the available inputs justify.

Instead, the calculators isolate energy and charging variables. Broader comparisons, such as EV versus petrol running cost, state clearly when they cover energy only rather than total cost of ownership.

Common questions

Why use usable battery capacity?

Usable capacity is the energy normally available to the driver. Gross capacity can include protective buffers that cannot be charged or discharged through the dashboard range.

Why divide by charging efficiency?

Because the wall supplies more energy than the battery stores. Dividing by efficiency converts battery energy into billable wall energy.

Why not estimate DC charging time from peak kW?

DC charging power changes throughout the session. Peak power is a maximum, not a constant rate.