Sourced fact
No charging-loss percentage is prefilled or applied without the user's choice.
Regulation · GB
Enter home charging loss explicitly
The calculator does not insert an unreferenced charging-loss percentage. Enter your own loss assumption only when converting battery-added kWh to estimated supply kWh. If the input already measures electricity bought for charging, do not add loss again.
Ofgem: Price cap unit rates and standing charges
Reviewed
Key facts and evidence
Within the UK, this Great Britain page is reviewed as of 13 August 2026. The conclusion is that charging loss must be a visible user input rather than a silent default, and it is unnecessary when supply kWh is already measured. The dated E2 tariff window is 2026-07-01 to 2026-09-30; no universal loss percentage is asserted.
Ofgem: Price cap unit rates and standing charges
Sourced fact
A loss input converts battery-added kWh into estimated supply kWh.
Sourced fact
An existing supply-side kWh measurement is not increased by a second loss adjustment.
Treat EV charging loss as a visible user input when converting battery-added energy into estimated electricity bought from the grid.
Visible conversion
Input: battery-added kWh and a user-entered loss percentage, defined here as the share of supply energy not added to the battery. Formula: estimated supply kWh = battery-added kWh ÷ (1 − loss percentage ÷ 100), followed by supply kWh × dated unit rate. Dated rate: the selected Ofgem row effective 2026-07-01 to 2026-09-30. No loss value is supplied automatically.
When loss is not added
If the input is already a supply-side or chargepoint reading of electricity bought for the charging session, that kWh value enters the cost formula directly. Applying another loss uplift would count the same conversion effect twice, so the loss control is disabled for this input type.
What to do next
Enter a loss assumption only when its purpose and the energy measurement boundary are understood.
Immediate action: Choose either measured supply kWh or battery-added kWh with an explicit loss input.
- Stop if the kWh measurement boundary or the basis of the loss assumption is unknown.
Professional hand-off
- Ask the chargepoint or vehicle data provider to explain its energy measurement before using it.
Questions this record can answer
What does the sourced evidence say about visible conversion?
Input: battery-added kWh and a user-entered loss percentage, defined here as the share of supply energy not added to the battery. Formula: estimated supply kWh = battery-added kWh ÷ (1 − loss percentage ÷ 100), followed by supply kWh × dated unit rate. Dated rate: the selected Ofgem row effective 2026-07-01 to 2026-09-30. No loss value is supplied automatically.
What does the sourced evidence say about when loss is not added?
If the input is already a supply-side or chargepoint reading of electricity bought for the charging session, that kWh value enters the cost formula directly. Applying another loss uplift would count the same conversion effect twice, so the loss control is disabled for this input type.