Your car and tariff
Finding your car's mi/kWh figure
Efficiency (miles per kWh) is the EV equivalent of MPG, and it's usually shown on the trip computer as a long-term average, sometimes labelled "efficiency" or given in the reverse unit kWh/100mi. A typical family EV manages 3 to 4 mi/kWh; smaller cars and gentle driving can exceed 4.5, while larger SUVs or motorway-heavy driving can drop below 3. As with MPG, use your own real-world average rather than the WLTP brochure figure, which is measured under ideal lab conditions.
Why your tariff changes everything
Electricity price is the single biggest lever in this calculator, and it varies more than fuel does at the pump. A standard variable rate sits around 24 to 30p/kWh as of mid-2026, but EV-specific tariffs with cheap overnight rates can bring that down to around 7p/kWh for charging scheduled in a set window, roughly a third of the standard-rate cost per mile. If you're serious about EV running costs, switching to an off-peak EV tariff and charging overnight is the highest-value change available, well ahead of driving style.
What this tool doesn't model
Cold weather increases energy use for cabin heating and reduces battery efficiency, so winter miles per kWh commonly runs 10 to 25% worse than the summer figure entered here. Battery degradation over the car's life very slowly reduces usable capacity, not modelled here since it's a multi-year trend rather than a per-charge cost. Standing charges on your electricity tariff, and any subscription fees for public charging networks, aren't included either; this tool prices the energy itself, per the tariff you enter.
Comparing against petrol or other tariffs
To see this figure next to a petrol car's running cost, use the EV vs petrol cost comparator. If you mix home and public charging, or want to see rapid charging's true cost per mile, the home vs public charging comparator lays out several tariffs side by side.