How much does home EV charging cost? Work it out properly

Collect the right inputs before calculating

For a battery-percentage calculation, you need usable battery capacity, starting charge, target charge, charging efficiency and a VAT-inclusive electricity rate. Use the usable capacity rather than automatically taking the largest battery number in a brochure. If your documentation gives several capacities or variants, check which applies to your car. Do not assume that two vehicles with a similar model name have the same battery.

For the price, read the tariff schedule or your current bill. Ofgem’s official price cap guidance distinguishes a unit rate, charged for each kWh, from a standing charge paid per day. A time-of-use tariff can have more than one unit price, so the hour of charging may change the answer. Headline national comparisons cannot substitute for your actual region, payment method and tariff conditions.

References: Ofgem — Understanding unit rates and standing charges

Calculate the energy stored in the battery

The starting formula is usable capacity multiplied by the change in percentage, divided by 100. A hypothetical 60kWh usable battery moving from 20% to 80% adds 36kWh: 60 × 60 ÷ 100. Moving the same battery from 50% to 80% adds only 18kWh. The target percentage alone does not tell you how much energy you need.

This simple model treats displayed battery percentage as proportional to usable capacity. It is suitable for planning, not billing verification of a specific vehicle’s battery-management system. If you are comparing recorded sessions, keep the same method and note any difference between energy reported by the car, the charger and your electricity meter.

Account for energy that does not stay in the battery

Charging efficiency is the fraction of grid electricity that reaches the battery in the model. At an assumed 90%, divide stored energy by 0.90. The 36kWh example therefore requires 40kWh from the grid. Multiplying by 0.90 would reduce the grid estimate below the battery energy and give the wrong direction of adjustment.

Use the efficiency setting to test uncertainty. At 85%, the same top-up needs about 42.35kWh; at 95%, about 37.89kWh. These values are sensitivity scenarios, not claimed measured efficiencies. At the illustrative £0.25 rate they produce the costs below. A range can be more honest than presenting one result to the penny without explaining its assumptions.

Convert the rate into the units the calculator expects

The calculator expects pounds per kWh for the UK. A rate of 25p/kWh should be entered as 0.25, not 25. For Ireland, a rate of 25 cents/kWh is €0.25/kWh. Selecting a currency changes the currency label; it does not convert a supplier’s tariff from pounds to euros. Enter a rate appropriate to the selected market.

If one session spans two prices, split the grid energy between the applicable rates. For example, 30kWh at an illustrative £0.10 and 10kWh at £0.30 costs £6 in total. Charging all 40kWh at the cheaper rate would cost £4, so treating the whole session as off-peak would understate that mixed-rate example by £2.

Estimate cost per mile and monthly driving

For a driving-based estimate, use miles per battery kWh together with charging efficiency. At an illustrative 3.5 miles/kWh and 90% charging efficiency, one grid kWh supports about 3.15 miles in this simplified model. At £0.25 per grid kWh, that is roughly £0.0794 per mile, or 7.94p. Do not divide by charging efficiency twice.

At 800 miles a month, the same assumptions imply about 228.6kWh of battery energy and 254.0kWh from the grid, costing around £63.49 if all of that driving energy is replenished at home. If only 80% is charged at home, the home portion is about £50.79. Public charging costs remain separate. You can substantially reduce this monthly cost by moving charging into an off-peak EV charging tariff.

Keep a session cost separate from the total bill

A standing charge is normally paid regardless of whether you charge the car that day. Adding the entire daily charge to every individual session can double-count it if there is more than one session. For a marginal session estimate, our tool excludes that fixed daily amount and explains the boundary.

When choosing a tariff, include it again at the household level. An illustrative difference of £0.10 per day is £36.50 over 365 days. Also include any change to the price of ordinary household electricity. The cheapest EV session can sit inside a more expensive overall tariff, which is why our annual EV tariff calculator includes separate EV and household consumption.

Compare estimates with actual use

To evaluate your setup, record a few sessions with starting and finishing percentages, duration and energy measured by the charger where available. Check what that reading includes and whether the relevant supplier rate was constant. Whole-home meter readings also include other appliances, so they cannot automatically be treated as EV-only consumption.

Use those observations to refine the assumptions rather than interpreting every difference as a fault. Temperature, auxiliary consumption, changing charging behaviour and measurement boundaries can affect comparisons. This guide offers a planning model; electrical problems or unexpected equipment behaviour should be assessed by the appropriate professional, not diagnosed from a cost calculation.

Run two scenarios before making a decision

First calculate a normal top-up with your current rate using our home EV charging cost calculator. Then change just one input: the rate, the target percentage or the efficiency assumption. Comparing scenarios one variable at a time makes the source of a saving visible.

After checking the cost, use the next-step link to estimate charging time with the same battery inputs, or explore our comparison of 7kW vs 22kW charging speeds. If you are considering a tariff switch, move on to the annual comparison and include household use and standing charges before acting.