What's this character's caster level? (theurge build)

[papr_weezl8472]

I have created a horrible abomination of spellcasting. The character itself is a Bard 1/Spellthief 1/Wu Jen 3/Ultimate Magus 1/Ur-Priest 3/Sublime Chord 1/Mystic Theurge 7/Ultimate Magus +1 (total character level 18).

The character has the feats Master Spellthief and Alternative Source Spell.

The first level of UM progresses bard, the second progresses Wu Jen/Sublime Chord. Sublime Chord keys off Wu Jen level to determine caster level (unless there's a better option available).

This abomination casts spells as a 2nd-level bard, a 4th-level Wu Jen, a 9th-level Sublime Chord and a 10th-level Ur-Priest.

Its caster level for all of these classes is a complex web of interconnected cross-referencing; Ur-Priest CL receives a bonus of half my levels in other spellcasting classes, Sublime Chord treats my caster levels in both Sublime Chord and Wu Jen as the sum of my class levels in both. Ultimate Magus 1 applies a global +1 to the caster level of my arcane spells. And on top of that I have Master Spellthief, which means my levels of Spellthief and my levels of all my arcane spellcasting classes stack to determine my caster level for all arcane spells.

So I put it to you, Playground: what the hell is this character's caster level? Or perhaps I should say caster levels; I think I have many, possibly different.

And finally, is there anything you'd suggest I change in the build?

[Biffoniacus_Furiou]

Your build is not legal. You need 13 ranks in Perform before you begin taking Sublime Chord, which is accomplished at 10th level. You have only nine class levels before Sublime Chord 1.

Ur-Priest is still a divine spellcasting class, tricking the game into thinking individual spells you cast with it are arcane at the time they're cast does not change that fact. It does not benefit from anything arcane-specific, including Sublime Chord and Master Spellthief caster level calculations.

"To determine the caster level of an ur-priest, add the character’s ur-priest levels to one-half of his levels in other spellcasting classes."
Your caster level of other classes is irrelevant, only your actual class levels will factor into your Ur-Priest caster level. Mystic Theurge has some unique wording which allows it to be counted along with your other classes, as well as directly increasing your effective Ur-Priest level. Any other prestige classes that advance spellcasting are not spellcasting classes themselves and will not contribute. With your current build, your Ur-Priest caster level is 16.

"A sublime chord’s caster level for both her sublime chord spells and the spells she gains from other arcane spellcasting classes is determined by adding her sublime chord level to her level in another arcane spellcasting class."
Again, this is counting only class levels, not caster levels, so your best choice is to pick Wu-Jen so you add +3 to your Sublime Chord caster level and +1 to your Wu-Jen caster level.

"Your spellthief and arcane spellcaster levels also stack when determining your caster level for all arcane spells."
That's not caster level but spellcaster level, i.e. the level which determines your spells/day and highest level spells available. Your arcane spellcaster levels are Bard 2, Wu-Jen 4, and Sublime Chord 9, plus you add Spellthief 1. Your base caster level for Bard is 16, Sublime Chord is 19, and Wu-Jen is 17, including the Sublime Chord bonuses, but not counting other bonuses such as Ultimate Magus' caster level bonus, Practiced Spellcaster, the Krau sigil of an Illumian, etc.