Armor class (AC) is a number representing a creature's ability to avoid being hit in combat. An opponent's attack roll must equal or exceed the target creature's AC to hit it.
AC = 10 + armor bonus + shield bonus + dodge bonus + natural armor bonus + deflection bonus + other bonuses
Effective AC = 10 + armor bonus + shield bonus + dodge bonus + natural armor bonus + deflection bonus + other bonuses + active armour (any reductions in the opponents AB (usually as a result of an offensive action))
The average, unarmored peasant has an AC of 10.
AC Types[]
armor bonus - provided by armor slot and bracers slot (bracers only; gloves provide deflection)
shield bonus - provided by shield slot
dodge bonus - provided by boots slot
natural armor bonus - provided by amulet slot
deflection bonus - provided by all other inventory slots
Only dodge bonuses stack, up to a maximum of +20. For all other types of bonus, the single highest modifier is applied.
Active AC - negative effects upon an opponents AB as a result of feats, spells and combat tactics.
As above, there are several types of armor class in Neverwinter Nights; some will work together (i.e., stack) and some will not. Knowing what stacks and what doesn't can often mean the difference between useful equipment and useless equipment.
Below are 7 AC categories; the 5 that NWN uses (natural, armor, shield, deflection, dodge), one extra "other" category to hold the bonuses that do not fit into the 5 base categories and the AC benefits that can be gained by targetting an opponent. All these categories will stack together, and ultimately sum together to form a character's effective AC. .
Sources of natural AC[]
These will not stack with each other; the highest one is used. **
- epic spell: epic mage armor (+5)
- item: amulet AC bonus (+1-7)
- spell: mage armor (+1)
- spell: barkskin (+3-5)
- spell: shadow shield (+5)
Sources of Armor AC[]
These will not stack with each other; the highest one is used. **
- epic spell: epic mage armor (+5)
- item: armor AC bonus (+1-7)
- item: bracers AC bonus (+1-7) (same item slot as gloves)
- spell: mage armor (+1)
- spell: magic vestment (+1-5)
Sources of Shield AC[]
These will not stack with each other; the highest one is used. **
- item: shield AC bonus (+1-7)
- spell: magic vestment (+1-5)
- feat: Dual wield defence. Three feats at +2 each
- ability : Duelist canny defence bonus - maximum of duelist level or int bonus..
Sources of Deflection AC[]
These will not stack with each other; the highest one is used.
- epic spell: epic mage armor (+5)
- item: gloves AC bonus (+1-7) (same item slot as bracers)
- item: ring AC bonus (+1-7) item: belt AC bonus (+1-7)
- item: helmet AC bonus (+1-7) item: cloak AC bonus (+1-7)
- item: weapon AC bonus (+1-7)
- item: dusty rose ioun stone (+1)
- spell: shield (+4)
- spell: mage armor (+1)
- spell: shield of faith (+2-5)
- spell: protection from alignment (+2 versus selected alignment)
- spell: magic circle against alignment (+2 versus selected alignment) (few Edon Belts and Helms grant significant armour but can be runed to do so. I am not aware of any "defender" type weapons and they can't be runed to do so)
Sources of Dodge AC[]
These will stack with each other, but is limited to a +20 maximum dodge bonus. *
- effect: haste (+4) epic
- spell: epic mage armor (+5)
- feat: bard song (+2-7)
- feat: divine shield (+1-20)
- feat: defensive stance (+4)
- feat: shadow evade (+1-4)
- item: boots AC bonus (+1-6)
- spell: mage armor (+1)
- spell: undeath's eternal foe (+4)
- spell: aura versus alignment (+4 versus selected alignment)
- polymorphing: you get a different bonus for different shapes. (dragonshape gives +20)All dodge AC is lost when caught flat-footed (even if the character has the uncanny dodge feat).
Other Sources of AC[]
These are all individual sources, and stack together with no restrictions.
- ability: dexterity (+1-122, but limited by the armor's maximum dexterity bonus) *
- feat: armor skin (+2) ** feat: battle training vs. giants (+4 against giant-type enemies)
- feat: bone skin (+2-16) **
- feat: dodge (actually gives you current target or last attacker -1 AB) *
- feat: draconic armor (+1-8) ** feat: expertise/improved expertise (+5/+10)
- feat: mobility (+4 against attacks of opportunity) *
- feat: monk AC bonus from level progression (+1-8) **
- feat: monk AC bonus from wisdom (+1-122) **
- feat: small stature (+1, or more generally the size modifier)
- item: armor base (+1-8) **
- item: shield base (+1-3) **
- skill: tumble (+1-8) *:
Active AC[]
These are effective AC 'gained' by reducing your opponent's AB. A way for builds with limited AC to get effectively 70+ AC. Not confirmed to be effected by any cap (except Word of Faith / Blindness and Darkness don't stack), but it is speculated that the most negative attribute you can apply to an opponent is -20.
- Spell: Interposing Hand (-10 AB)
- Spell: Negative energy burst (-1 to -4 AB)*
- Spell: Battletide (-2AB)Spell: Prayer (-1AB)
- Spell: Word of Faith / Blindness (+ 25% to 50% enemy miss chance)**
- Spell: Darkness (+25% to 50% enemy miss chance)***
- Feat: Called Shot (-2 to -16 AB)Feat: Curse Song (-2 AB)
- Effect: Blinded (-4 AB)**** By reducing enemy strength, only against str-based opponents** 25% if opponent has
- Blindfight*** No effect if enemy has True Sight or Ultravision
- By reducing enemy strength, only against str-based opponents
** 25% if opponent has Blindfight
*** No effect if enemy has True Sight or Ultravision
Original article written by Rothbart with additons by LeFire and Tuckos