How do I calculate a blended home and public charging price?

Suppose 150 billed kWh costs 0.20/kWh at home and 50 billed kWh costs 0.60/kWh publicly. The energy cost is 30 + 30 = 60 for 200 kWh, or 0.30/kWh. Averaging the two displayed prices would give the wrong answer because the quantities differ.

If those sessions also incur 8 in connection and parking fees, the effective total becomes 68 ÷ 200 = 0.34/kWh. Keep an energy-only figure as well if you want to compare tariffs. Label clearly whether fees are included.

Home wall-meter kWh and public billed kWh are purchased-energy quantities. Battery-energy figures describe a different boundary. Do not mix them into the same weighted average without explaining the conversion and its uncertainty.

If the same accounting period covers 1,000 km, 68 in charging costs corresponds to 0.068 per km. A large difference between starting and ending charge can distort a single month; longer comparable periods can give a more useful running-cost picture.

Repeat the calculation with more expensive public energy if home charging becomes unavailable. That scenario answers whether the budget survives a change in routine, rather than simply reproducing the cheapest month you can imagine.