kWh per mile is the bridge between driving habits and home charging cost. A practical estimate divides metered charger energy by miles driven over the same period, after noting whether some miles were publicly charged. Brochure figures are a starting point only. Weather, speed, heating, load and tyre condition move the result. Once you have a stable kWh per mile, multiply by miles and by the illustrative or contract unit rate that applied to those charging hours. Keep standing charges out of the per-mile energy maths unless you are building a whole-bill model.
Two ways to estimate
Method one uses the car's trip computer efficiency readings over a representative month. Method two uses wallbox delivered kWh divided by odometer miles, adjusted for public charging sessions logged in apps.
Wallbox energy includes charging losses that trip computers sometimes present differently. For bill forecasting, metered home kWh is the more honest numerator.
Build a representative sample
A single motorway week will not match a mixed urban month. Capture at least two to four weeks that look like your normal routine, then repeat in winter if you can.
Note cabin preconditioning from plugged power. It can be efficient for comfort yet still adds home kWh that drivers forget to attribute to the car.
- Log home kWh weekly from the charger app.
- Log public kWh separately.
- Record miles from the odometer, not guesswork.
From efficiency to cost
Example: 0.28 kWh per mile and 800 miles in a month implies about 224 kWh. At an illustrative 16p per kWh off-peak blended home rate, energy is about £36. At an illustrative 30p flat rate, about £67. Your tariff file wins over these illustrations.
If half the energy was public at a higher rate, blend the cost. Do not apply the home rate to miles you did not charge at home.
Why winter changes the number
Battery chemistry, cabin heat, higher rolling resistance and more defrost cycles commonly raise kWh per mile. Range anxiety can also push drivers to charge more opportunistically at expensive locations.
Update the estimate seasonally rather than arguing with a summer figure in January.
Using the estimate in household planning
Efficiency helps size whether a time-of-use window is long enough, whether solar diversion is meaningful, and whether a second EV fits the budget.
It does not replace a surveyed install quote. Capital cost bands and running cost estimates answer different questions.
Frequently asked questions
Is WLTP enough for home cost estimates?
It is a standardised comparison tool, not a promise. Real driving and climate usually differ.
Should I use rated miles or odometer miles?
Use odometer miles for cost work. Rated range is for vehicle shopping comparisons.
Do charging losses mean my car is inefficient?
Some energy is always lost as heat in cabling and conversion. Comparing metered wallbox kWh to miles already includes that real cost of home charging.
How often should I refresh the estimate?
After major season changes, tyre changes, or a shift in commute pattern. Otherwise a quarterly check is plenty for most households.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local EV Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.