Skills/Concentration

A character usually must make concentration checks whenever you might potentially be distracted, such as by taking damage, while engaged in an action that requires your full attention. Primarily this includes actions such as casting a spell, or concentrating on an active spell. If the Concentration check succeeds, you may continue with the action as normal. If the check fails, the action automatically fails and is wasted.

As a skill concentration is primarily a focus of casters, but certain classes or actions may require a concentration check.

Action
None. Making a Concentration check doesn’t take an action; it is either a free action (when attempted reactively) or part of another action (when attempted actively).

Try Again
Yes, though a success doesn’t cancel the effect of a previous failure, such as the loss of a spell you were casting or the disruption of a spell you were concentrating on.

Special
To cast a spell you must concentrate. If something interrupts your concentration while you’re casting, you must make a concentration check or lose the spell. When you make a concentration check you roll 1d20 + Concentration Skill (skill ranks, skill modifier, and any other miscellaneous bonuses to the concentration skill.)

Casting Defensively
When casting a spell you leave yourself open as you attempt the casting, you may avoid this by making a concentration check to both keep your defenses raised while casting the spell. The DC of this is 15 + the BCB of the spell. Should you succeed you cast the spell and do not provoke an attack of opportunity. Should you fail you cast the spell as normal but provoke an attack of opportunity, which in itself may be subject to a concentration check.

Injury
If you take damage while trying to cast a spell you must make a concentration check with a DC equal to 10 + the damage taken + ½ the BCB of the spell. If you fail this check you lose the spell without effect.This interrupting event strikes during spellcasting if it comes between the time you started and the time you complete a spell. Damage taken to temporary hit points still counts as damage for the purposes of determining the DC of the concentration check.

If you are maintaining an already cast spell or taking continuous damage (such as a bleed effect) the DC instead becomes 10 + ½ the damage taken + ½ the BCB of the spell you are casting. If the continuous damage dealt was the last damage the effect could deal (such as the bleed duration ending), then the damage is over and does not distract you.

Grappled, Pinned, or Entangled
If grappled or pinned the DC is The grappler’s last combat maneuver check used to establish or maintain the grappled + ½ the BCB of the spell you’re casting. If entangled the effect is simply 15 + ½ the BCB of the spell you’re casting. These effects usually restrict the motions of the caster in some way making for a distraction to their casting.

Motion
Motion is broken down between Vigorous, Violent, or Extreme motion. In vigorous motion such as a mount, wagon ride, or a boat in rough water you may be subject to a DC 10 + ½ the BCB of the spell concentration check. Violent motion such as a boat in rapids or a storm requires a DC of 15 + ½ BCB of the spell concentration check. Extreme motion such as an earthquake has a DC of 20+½ the BCB of the spell concentration check.

Weather
Blinding rain or sleet can be a distraction requiring a DC 5 + ½ the BCB of the spell concentration check to cast the spell. While hail, dust, debris can be more distracting requiring a DC 10 + ½ the BCB of the spell concentration check to cast the spell.