I was never entirely clear on how it works for spells.


1 Answer 1


Concentration is used to resist being interrupted, cast without provoking attacks, or get a spell out in a difficult situation.

According to the SRD, when you take damage while casting a spell (typically from an attack of opportunity or from a readied attack), you have to make a concentration check DC of 10+ the damage that you took while casting.

Defensive Casting lets you roll before you cast, to not provoke attacks of opportunity for casting the spell, with a DC of 15 + The level of the spell you're trying to cast.

On the page I linked, there is also a table of examples of situations that would require a concentration check to cast a spell, such as bouncing around on a horse, being Grappled, or in the middle of a storm.

The Concentration skill is not required to cast spells, but it is very, very useful.

  • 5
    \$\begingroup\$ It might be useful to mention that failing the Concentration check when casting on the defensive does not mean that the caster provokes an attack of opportunity but, instead, that the caster loses the spell! A caster really wants to succeed on those checks. \$\endgroup\$ Jan 13, 2017 at 9:51

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