Does an EV save money? Start with the cost of 100 km
A battery refill price is not a fair comparison: two cars may travel different distances using the same energy. Start with equal distance and prices you actually pay.
Turn consumption into cost
Multiply kWh per 100 km by the price per kWh. For petrol, multiply litres per 100 km by the price per litre. Multiply either result by monthly kilometres ÷ 100. Battery capacity is not driving consumption.
Choose a representative electricity price
The U.S. Department of Energy explains charging costs using consumption and electricity prices, which can vary by charging time. Weight home and public prices by their share of energy, not the number of sessions.
References: U.S. Department of Energy — Charging electric vehicles at home
Keep the comparison honest
Metered electricity already includes charging losses. For battery-side consumption, divide by efficiency: 18 ÷ 0.90 = 20 paid kWh. Do not add losses twice. Session fees, subscriptions, the charger, insurance and maintenance need a separate ownership comparison.
Example: a mix of home and public charging
At 1500 km monthly and 18 paid kWh/100 km, charging 80% at 0.20 and 20% at 0.60 gives a weighted price of 0.28 and monthly energy cost of 75.60 currency units.
A petrol car using 7 L/100 km at 2 per litre costs 210 monthly. The difference is 134.40 monthly or 1612.80 annually if use stays constant. These are illustrative prices, not live tariffs or a promise that an EV is always cheaper.