Additional Caster Levels from more than one PrC

[TessarrianDM]

A player in my group has a Cleric 3/Wizard 3/Mystic Theurge 10/Sorcerer 1. He wants to take levels in Ultimate Magus. Do the additional caster levels gained in a prepared spellcaster class granted by the Ultimate Magus stack with those granted by Mystic Theurge?

 

[Dandu]

UM advances one prepared arcane spellcasting class and one spontaneous spellcasting class. The wizard side would receive advancement, but not the cleric.

Incidentally, that's a horrible build.

 

[Herzog]

If you mean: does a Cleric 3/Wizard 3/Mystic Theurge 10/Sorcerer 1/Ultimate Magus 10 have the spellcasting of a 20th lvl wizard: yes.
(UM spellcasting progression is 7/10 for highest class)

If you mean: does the Mystic Theurge count as a spellcasting class, implying that both cleric and wizard would gain additional spellcasting levels: no.

If you mean: does a Cleric 3/Wizard 3/Mystic Theurge 10/Sorcerer 1/Ultimate Magus 1 have the spellcasting of a 15th lvl Sorcerer (implying the Mystic Theurge adds lvls to the sorcerer class as well): no

@Dandu: Powerwise, it indeed looks like a horrible build. On the other hand, if you go for low level spellslots in abundance (and you have the stats for it), it looks interesting. Beguiler or something like that might be a better choice than sorcerer, however.

 

[TessarrianDM]

If you mean: does a Cleric 3/Wizard 3/Mystic Theurge 10/Sorcerer 1/Ultimate Magus 10 have the spellcasting of a 20th lvl wizard: yes.
(UM spellcasting progression is 7/10 for highest class)

This. So, he would wind up casting spells as a Cleric 13/Wizard 20/Sorcerer 11, correct?

 

[Herzog]

Yes.

He'd be a 27th lvl character though (assuming no Level Adjustments or Racial Hit Dice)