Methodology version 1.0 · 16 September 2026

Every number has a formula

A transparent energy comparison using your assumptions. No hidden vehicle scores or price forecasts.

1. Battery consumption to billed electricity

EV consumption means energy drawn from the battery per 100 km. Charging loss is the share of electricity measured at the meter that does not reach the battery.

Metered energy = battery consumption / (1 − loss / 100)

18 kWh from the battery with 10% loss requires 20 kWh from the meter. If your consumption figure already includes charging losses, set loss to 0. Starting values are illustrative assumptions, not specifications of a particular car.

2. Your blended electricity price

Blended price = home price × home share
              + public price × (1 − home share)

The home share is a share of energy, not charging sessions. 80% at €0.30/kWh and 20% at €0.59/kWh gives €0.358/kWh. One common loss rate is used for both charging types. Time, connection, parking and subscription fees are excluded; account for them in an effective kWh price if relevant.

3. Energy costs and savings

EV per 100 km = metered energy × blended price
Petrol per 100 km = litres per 100 km × price per litre
Annual saving = (petrol cost − EV cost) × annual km / 100

The starting example gives €7.16 versus €11.70 per 100 km. At 15,000 km, that is €681 of annual energy savings. A negative saving means the EV uses more money on energy under those assumptions.

4. Purchase difference and payback

Premium = EV price − petrol price + additional charger cost
Balance = annual saving × years − premium
Payback km = premium / saving per 100 km × 100

Payback requires a positive upfront premium and positive energy savings. Payback in years also requires positive annual mileage. If the EV is already cheaper upfront, we show the period balance rather than a misleading negative payback time. Consumption and prices remain constant, and future payments are not discounted.

5. Electricity break-even price

Break-even electricity price = petrol cost per 100 km / metered energy per 100 km

This is the average price across your whole charging mix. Below it, EV energy costs are lower. It does not account for a vehicle purchase premium or other ownership costs.

What is missing?

Depreciation, resale value, interest, leasing payments, insurance, maintenance, vehicle taxes, subsidies and individual repairs. This is therefore not a full total-cost-of-ownership comparison. Winter, speed, route and load change consumption; enter figures appropriate to your driving. We do not calculate emissions or claim environmental benefits.