EV Charging Loss Calculator
Charging loss is the difference between energy drawn from the supply and energy stored by the battery over a matching session. It is not always all conversion loss because conditioning and auxiliary loads may be included.
How to use this calculator
- Enter matching wall-energy and battery-energy readings in kWh.
- Check that units, denominator definitions and time periods are consistent before comparing scenarios.
- Run a second scenario when an assumption is uncertain.
Formula used by ev charging loss calculator calculator
Energy difference = wall energy − battery energy; wall-to-battery efficiency (%) = battery energy / wall energy × 100.
- Energy difference = wall energy − battery energy; wall-to-battery efficiency (%) = battery energy / wall energy × 100.
- Use paired measurements from the same session. A result above 100% generally means the readings or energy boundaries are inconsistent.
- The tool performs arithmetic on the values entered and does not validate assumptions against outside records.
Worked examples
Worked example
63 kWh drawn from the wall and 55 kWh added to the battery.
Loss = 8 kWh; wall-to-battery efficiency = 55 ÷ 63 × 100 ≈ 87.30%.
The session shows 8 kWh difference and approximately 87.3% efficiency.
Understanding the result
Charging loss is the difference between energy drawn from the supply and energy stored by the battery over a matching session. It is not always all conversion loss because conditioning and auxiliary loads may be included.
Use paired measurements from the same session. A result above 100% generally means the readings or energy boundaries are inconsistent.
Important notes
Use paired measurements from the same session. A result above 100% generally means the readings or energy boundaries are inconsistent.
Treat this output as an estimate tied to the stated inputs. For regulated, safety-critical, tax or professional decisions, verify applicable official guidance and specifications.
Frequently asked questions
Does this measure charger efficiency alone?
No. It can include vehicle heating, cooling and other auxiliary loads.
Why can two sessions differ?
Temperature, charging power, state of charge and conditioning can change losses.
How should I interpret the result?
Use paired measurements from the same session. A result above 100% generally means the readings or energy boundaries are inconsistent.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.