Correct. Mystic Theurge levels do not count as levels in your previous classes.
Like many of the other prestige classes, levels of Mystic Theurge stack with the spellcasting features of the character's previous classes, but do not otherwise stack with the other class features.
When a new mystic theurge level is gained, the character gains new spells per day as if he had also gained a level in any one arcane spellcasting class he belonged to before he added the prestige class and any one divine spellcasting class he belonged to previously. He does not, however, gain other benefits a character of that class would have gained. This essentially means that he adds the level of mystic theurge to the level of whatever other arcane spellcasting class and divine spellcasting class the character has, then determines spells per day, spells known, and caster level accordingly.
Levels of Mystic Theurge stack with your cleric and wizard abilities as follows:
- Add your MT level to your effective caster level for cleric spellcasting and wizard spellcasting. This affects any calculation that involves "caster level", such as spellcasting range (close, medium, long), concentration checks, and caster level checks.
- Add your MT level to your cleric level to determine cleric spells per day.
- Add your MT level to your wizard level to determine wizard spells per day.
Your MT level is not added to anything else. If something specifically refers to your "cleric level" or "wizard level" (such as divine domain, arcane school, or the Command Undead feat) then you only count the levels you have in that class.
