Larian Studios Forums Baldur's Gate III Baldur's Gate III - General Wrong number of spell slots?

Did some more testing, but I don't have enough time to fully explore this. Right now I think that the following is happening...

If you have a single class of half or third caster, the game rounds up to determine ESL (example EK 4th level rounds 4/3 up to 2).
If you have two third casters (EK and Arcane Trickster) then you sum the levels, divide by three, and round down (example, EK+Arcane doesn't get ESL 3 until the sum of the classes is 9).
If you have two half casters (Pally and Ranger) then you sum the classes and round down (ESL goes up on even levels)

EDIT:

for the original EK + Pally that inspired the thread, it appears that you add EK/3 + Pally/2 and round down. IMO it should round up to be consistent with single class pally or EK progression.