You can add the same metamagic feat to a spell more than once.
Benefit: You can add some metamagic feats to a spell more than once. Only spells that increase one of the numeric values of a spell by a set amount can be stacked. Thus you can stack multiple Defensive Spell, Empower Spell, Enlarge Spell, Extend Spell, Profane Spell, Sanctified Spell, and Widen Spell feats onto the same spell. Each additional use of the metamagic feat adds the same total amount to the numeric value of the spell effected. Thus an “extended extended” spell has triple the duration of a normal spell (each Extend Spell adding a duration equal to the spell’s original value), and a “profane profane” spell deals all unholy damage, and good creatures are at a –2 penalty to saves against it.
When stacking metamagic feats, the spell uses up a spell slot equal to its normal spell level + the total number of levels added by the metamagic feats +1. Thus an “extended extended” spell uses up a spell slot three levels higher than the spell’s actual level (+2 for the two uses of Extend Spell +1).