EV Home Charging Cost Calculator

Understanding the EV home charging cost calculator — concept and principle

Charging an electric car at home is usually the cheapest way to run it, but the cost depends on how much energy you add, how much is lost during charging and your electricity tariff. This calculator estimates the cost of one charge, the cost per 100 km and the driving range that charge adds.

You pay for the 55.6 kWh drawn, not the 50 kWh stored: $13.89 a charge.

How it is calculated

Energy from the grid = battery energy added ÷ (efficiency ÷ 100)
Cost of this charge = grid energy × price per kWh
Cost per 100 km = consumption (kWh/100 km) ÷ (efficiency ÷ 100) × price
Range added (km) = battery energy added ÷ consumption × 100

Battery energy is the kWh you put into the pack, for example from 20% to 80% of a usable capacity. Efficiency covers losses in the charger, cables, battery and cooling. Consumption is the car's average energy use from its trip computer.

The principle

Not all electricity from the wall ends up stored in the battery. The onboard charger converts AC to DC, the battery warms slightly and cooling systems may run, so the meter records more energy than the battery gains. Dividing by efficiency converts battery energy back to metered energy. Home charging efficiency is commonly around 85–95%, and low-power charging from a standard socket tends to be at the lower end because fixed overheads last longer. Consumption, by contrast, is measured from the battery, so range uses battery energy directly.

Worked example

Inputs: 50 kWh added, 90% efficiency, $0.25 per kWh, 17 kWh/100 km.
Grid energy: 50 ÷ 0.90 = 55.56 kWh.
Cost of this charge: 55.56 × $0.25 = $13.89.
Cost per 100 km: 17 ÷ 0.90 × $0.25 = $4.72.
Range added: 50 ÷ 17 × 100 = 294.1 km.

Each point is the calculator re-run with only “Charging efficiency (%)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Charging efficiency (%)	Cost of this charge
22.5	$55.56
45	$27.78
67.5	$18.52
90	$13.89
112	$11.11
135	$9.26
180	$6.94

How to read the result

Cost per 100 km is the best figure for comparing with a petrol or diesel car: multiply that car's litres per 100 km by the fuel price. Off-peak or EV tariffs can lower the price dramatically, so enter the rate that applies at your charging time. Winter driving, motorway speeds and heating raise consumption, so expect a higher cost per 100 km and less range in cold weather.

Common mistakes

Entering the full battery capacity when you only add part of it.
Using 100% efficiency, which understates cost.
Using the daytime tariff for overnight charging.

Keep in mind: Results assume constant efficiency and consumption. Real figures vary with temperature, speed and charger type. It is not financial advice.

Frequently asked questions

How do I convert km/kWh to kWh/100 km?

Divide 100 by the km/kWh figure; 5.9 km/kWh is about 17 kWh/100 km.

Why does the wall meter show more than the car?

The difference is charging loss, which is what the efficiency input accounts for.

Is charging to 100% more expensive?

Per kWh it costs the same, but many makers recommend a lower daily limit for battery health.

Sources: International System of Units (SI), BIPM · U.S. Department of Energy, Alternative Fuels Data Center — charging electric vehicles at home

Checked 8 Nov 2026. Typical coverage rates and standard formulas. Always check the product label and local building rules; buy 5–10% extra for waste.

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