A difficulty class, or DC, is the number that a player must meet or beat after rolling a d20 and adding modifiers to succeed in a check or saving throw. Difficulty classes are generally given in spell or item descriptions.
DC in spells
- DC = 10 + (spell level) + (spellcaster's ability modifier) + (spellcaster's feat bonuses) + (epic bonus)
The spellcaster's ability modifier is the modifier for the spellcaster's spellcasting ability: intelligence for wizards; charisma for sorcerers, bards, spirit shamans, and warlocks; and wisdom for clerics, druids, favored souls, rangers, and paladins.
The spellcaster's feat bonuses include Spell Focus (+1), Greater Spell Focus (+2), and Epic Spell Focus (+3). Spell Focus feats do not stack with each other; only the highest one applies. The Red Wizard's Enhanced Specialization is treated as a feat bonus. It, however, does stack with Spell Focus feats.
Epic Bonus: All spellcasters receive a +1 bonus to their DC's for every 3 caster levels over 20 (i.e. +1 at level 23, +2 at level 26, etc.). The source of these caster levels does not matter. Caster levels obtained from a Prestige Class or from Practiced Spellcaster both contribute to the total caster level used for the Epic Bonus.
Note: Epic Spells do not apply the spellcaster's feat bonuses. However, they do all come with an inherent +5 bonus. The DC for making a saving throw against an Epic Spell is:
- DC = 25 + (spellcaster's ability modifier).
A roll of 1 always fails a saving throw and a roll of 20 always succeeds, so saving throws always have at least a 5% chance of failure and a 5% chance of success.
Simple Example: Suppose a wizard with 18 intelligence and Spell Focus (Evocation) cast a Fireball against a goblin. To take half damage, the goblin needs to make a reflex save against a DC of 18: 10 from the base DC + 3 from Fireball's level + 4 from the intelligence modifier + 1 from the spell focus feat. If the goblin has a reflex save of 3, he has to roll at least 15 on his d20 to make the saving throw.
DC in skill checks
The DC depends on the skill. For example, the DC for tumbling is 15, the DC for casting a spell in defensive casting mode is 15 + the level of the spell, and the DC for disarming a trap depends on the trap.
In the official campaign, the DC's for dialogue skills like bluff and diplomacy are set. These values are roughly as if the user had taken 10 on the skill check, so a DC of 1 (you'd need 1 point in the skill to pass) roughly equals a normal skill check of DC11. Medium DCs range from 6-8, while hard ones exceed 15. Other modules use different systems.
In contrast to saving throws, skill checks never fail or succeed automatically. A roll of 1 may succeed if the skill is high enough and a roll of 20 may fail if the skill is too low. This means characters with enough skill will always make some skill checks, such as the concentration check for casting a spell in defensive casting mode or the tumble check for avoiding attacks of opportunity when moving past or away from enemies.