Spontaneous Metamagic

A spellcaster can choose to use the “Spontaneous Metamagic: Daily Uses” Variant in Unearthed Arcana, page 152, when using metamagic feats. A character can still prepare metamagic spells in the normal fashion if they prefer. All uses of a specific metamagic feat for the day must be either “Spontaneous” or “Normal” method. They cannot be mixed within the same feat. However, if a spellcaster has access to multiple metamagic feats, he can choose to apply “Spontaneous” or “Normal” to each independently.

Spontaneous: Daily Uses

With this variant, a character who selects a metamagic feat gains three daily uses of that feat that she can opt to use “on the fly” without previous preparation, increased spell level, or extended casting time. The character must decide when casting the spell if she wishes to apply the effect of one of her metamagic feats to the spell.
The maximum level of spell to which a caster can apply a metamagic feat is equal to the maximum spell level she is capable of casting (based on her level and ability scores), minus the spell level adjustment of the metamagic feat. If the result of this calculation is less than 0, the character can’t apply the metamagic feat to any of her spells.
For instance, a 5th level wizard is normally capable of casting spells of up to 3rd level. If she chooses to apply her Silent Spell metamagic feat (which uses a spell slot one level higher than normal) to a spell, the maximum level of spell that she can apply it to is equal to 3 minus 1, or 2nd. Thus, she may make any of her 0, 1st, or 2nd level spells silent. If she had the Maximize Spell feat, she could apply it only to 0-level spells (since a maximized spell is normally cast as a spell three levels higher, and 3 minus 3 is 0). Quicken Spell would be of no use to this wizard, since she couldn’t even apply it to 0-level spells.
A caster can apply more than one metamagic feat to a spell, or even the same metamagic effect more than once (if allowed by the feat’s description). However, to determine the maximum level of spell that can be so affected, add together all the spell level adjustments given for the various feats. A 9th level wizard could enlarge and empower any spell of 2nd level or lower (since her maximum spell level is 5th, and the total spell level adjustment for Empower Spell and Enlarge Spell is 3). If a feat may be applied more than once to the same spell (such as Empower Spell), each application counts as one of the caster’s three daily uses.
Each time a character selects a metamagic feat, she gains three daily uses of that feat. Multiple selections of the same feat are cumulative. For instance, if a caster selects Empower Spell twice, she may use the feat six times per day rather than three.
In this variant system, the Heighten Spell feat functions slightly differently from other metamagic feats. You may use the Heighten Spell feat to increase a spell’s effective level (for purposes of such factors as save DCs and so on) up to the maximum spell level you are capable of casting. For instance, a 3rd level cleric could heighten a 0 or 1st level spell to 2nd level, while a 17th level druid could heighten a 0 through 8th level spell to 9th level. The spell is treated as a spell of that level for purpose of save DC and similar effects, but doesn’t require a higher-level spell slot.