Home vs public EV charging: compare the real energy cost
A single p/kWh headline is useful, but most drivers use a mixture of home, off-peak and public charging. A blended cost makes that mix visible.
Start with a weighted charging price
Example: 70% at 8p/kWh, 20% at 35p/kWh and 10% at 75p/kWh gives a blended purchased-energy rate of 20.1p/kWh.
Convert the rate into cost per mile
If a car achieves 3.5 mi/kWh at the battery and charging efficiency averages 90%, it needs roughly 0.317 kWh from the charger per mile. At a blended 20.1p/kWh, energy cost is about 6.4p/mile. At 75p/kWh public charging alone, the same assumptions produce about 23.8p/mile.
When does a charging membership pay?
If a network charges a monthly fee in exchange for a lower p/kWh rate, the simple break-even quantity is:
A £7.99 monthly fee with a 12p/kWh discount breaks even at about 66.6 kWh/month. Below that, the subscription costs more than it saves on the stated rates.
Costs not captured by an energy-only comparison
Parking fees, idle fees, subscription fees and route detours can matter at public chargers. At home, charger installation and tariff effects on household electricity are separate decisions. Keep the energy calculation transparent, then add those costs only when they apply to your decision.
Use the mix you expect over a year
A driver with reliable home charging might public-charge only on occasional long trips, while a driver without off-street parking could have the opposite mix. The same vehicle therefore can have very different annual energy cost. Weight the prices by the share of energy bought at each rate, not simply by counting charging sessions: one 60 kWh rapid charge should not have the same weight as a 6 kWh top-up.
If public charging is a major share of your use, test both ordinary PAYG and any membership rate you would genuinely qualify for. Then add the membership fee separately rather than hiding it inside an assumed p/kWh number.