How We Calculate EV Charging Costs

Every cost figure on this site comes out of the same formula, using sources we name. This page lays the whole thing out, so you can check our arithmetic or swap in numbers of your own.

The formula

Cost per mile works out as:

(kWh per 100 miles ÷ 100) × your electricity rate ÷ charging efficiency

Three inputs, and only one of them is really ours to estimate.

Where each input comes from

Consumption (kWh per 100 miles). Straight from the EPA’s published efficiency rating for that model and model year. We use the combined figure unless an article is specifically about highway or city driving.

Electricity rate. This is the one that makes national averages so unhelpful. Rates vary by more than a factor of three across the US, and time-of-use tariffs can vary by a factor of two within a single day. We start from your state’s published average and let you override it — because the number on your own bill is the only one that really counts.

Charging efficiency. Energy pulled from the wall is always more than energy that ends up in the battery. We assume 90% for Level 2 home charging. That is an estimate and we’d rather flag it than let it pass quietly: real losses shift with temperature, charge rate and state of charge.

What we leave out

We keep these separate rather than burying them inside a cost-per-mile figure:

• Charger installation — a one-off bill, not a running cost
• Battery degradation — real, but far too model-specific to average honestly
• Incentives and rebates — they expire and vary by location, so they get their own dated articles rather than being baked into a formula

When these numbers go stale

Tariffs get revised and incentives run out. Every figure here carries the date we checked it. If you’re reading a page where that date is more than a year old, treat the number as a starting point and go and check your current tariff — and if you spot something that’s drifted, do tell us.