I'm sure there are multiple variables to account for charging loss, which people more adept at engineering than me can explain.
What do you use to charge your car? I have the Chargepoint Flex and and it tells me the amount of energy 'delivered' with each charge, so I can roughly calculate energy loss based on the battery state of charge.
For example, last weekend I charged from 10% to 80%. Based on the API website made by
@segbrk, my current battery capacity is 105.25 kWh (~7% degradation over 22k+ miles). Therefore the car should have received 73.675 kWh (105.25 x 0.7). My Chargepoint said it delivered 82.23 kWh, which means there were almost 9 kWh lost. There's a chance my battery was actually at 9%, so the loss may be a little less, but it'd still be around 10%.
Is this the sort of thing you're looking for?