[3.e] Ur-Priest, Mystic Theurge, and Caster Levels

[El Chupaqueso]

So, I'm working on statting out a BBEG for a campaign, and he has a sort of unusual build which makes it rather hard to determine his caster level. He's got Dread Necromancer 5 / Ur-Priest 2 / Mystic Theurge 8. I know his caster level as a Dread Necromancer is 13, but the Ur-Priest is more complicated.

BoVD says, "To determine the caster level of and ur-priest, add the Character's ur-priest levels to one-half of her levels in other spellcasting classes."

This is where I'm unclear. Do I add his actual ur-priest levels (2) to half of his levels in Dread Necromancer and Mystic Theurge? Or do I take his ur-priest caster level including Mystic Theurge (10) and add it to half of his Dread Necromancer levels? Or do I do that, but add it to half of his Dread Necromancer levels including their advancement by Mystic Theurge as well? Also, when dividing in half, do I round up or down? BoVD doesn't say.

Since I'll probably get conflicting interpretations, it would be helpful if someone actually had some relevent errata to provide a definitive answer. Thanks in advance!

[Mongoose87]

To look at it one way, your caster level in Dread Necro = Dread Necro+ Theurge, so you'd take (Dread Necro+ Theurge)/2.

[FMArthur]

There's no errata that changes that, to my knowledge (the Complete Divine Ur-Priest has it written the same way). I would say that "other spellcasting classes" excludes the one making the reference, and since Mystic Theurge effectively inherits that statement and includes itself in Ur-priest casting advancement, I'd rule that it's half of your Dread Necro levels, plus your Ur-Priest levels, plus any other levels that advance your Ur-priest casting.

[El Chupaqueso]

I think I'll go with that second one for now, because adding (Dread Necro + Theurge)/2 would give him a caster level higher than his character level, which just doesn't seem quite right.