Difficulty class (DC) is a number that describes how hard a particular action is, with higher numbers indicating harder actions. When a character's action has a DC, a die roll determines whether or not that action is successful. If the roll of a d20 plus applicable modifiers is at least the DC, then the action succeeds; if it is less than the DC, then the action fails.
One action associated with a DC is the use of a skill. The DCs for these skill checks are determined using various methods, as indicated in each skill's description. Two common methods are opposed checks and explicit formulas. For most other skills, the DC is set (or left as the default) by the module designer.
Another action associated with a DC is an attempt to avoid a harmful effect. This attempt is called a saving throw. Saving throw DCs for spells, non-spell item properties, monster special abilities, feats, traps, and creature auras are described below. Saving throws provide an exception to the success/failure rule: if the die roll is a natural 20, then the save is successful, even if the DC is not met. On the other hand, if the die roll is a natural 1 and the game's settings have auto-fail turned on, then save fails, even if the DC is met.
When a spell allows a saving throw, the DC is determined by the spell level, the caster's primary ability modifier (for the ability on which their spells are based), and the caster's feats, as follows:
- DC = 10 + spell level + ability modifier + feat modifier.
The feat modifier is +2 for spell focus, +4 for greater spell focus and +6 for epic spell focus. The feat modifiers are not cumulative. Spells cast from items do not factor in the caster, instead assuming a standard combined ability/feat modifier of +3; that is, the DC is 13 plus the spell's innate level.
Item properties that are not spells often have a preset DC that depends on which property is being considered. Some of these properties list their DCs in the name of the property, as in "on-hit: stun (DC=14)".
- 10 + innate level + charisma modifier.
Abilities given by feats, if not otherwise specified, have a DC of
- 10 + class level + ability modifier.
The ability in question is the primary ability for the class granting the feat. In a few special cases, a negative primary ability modifier triggers a bug that causes the DC to become rather large (127 or more). These special cases are fear (feat), shadow daze, sleep (feat), and custom feats whose script combines
When a trap allows a saving throw, the difficulty class is determined by the type and strength of the trap.
- The DC for the planar binding spell is the above formula plus 2.
- The DC for the implosion spell is the above formula plus 3.
- The DC for the hold animal spell is the above formula plus 4.
- The DC for the greater planar binding spell is the above formula plus 5.
- The DC for the dismissal spell is the above formula plus 6.