Effect stacking refers to the combined impact on a single effect from multiple sources, including equipment, skills, and environment. Typically, effects stack by adding the totals from all sources, however some effects are capped, some sources have their contribution capped, and other effects might combine under a more complex formula.
 Types of stacking
 Equipment bonuses
- Most armor bonuses stack, but a few upgrades do not; these are labeled as "non-stacking".
- The strongest non-stacking bonus takes precedence over the others, but all the penalties are applied.
- For example, an elementalist equipped with runes of Superior and Major Energy Storage will receive only +3 to their Energy Storage attribute (the maximum bonus), but will lose 110 of their base health (the sum of the -35 and -75 health penalties).
- Headgear attribute bonuses always stack.
- Armor rating and damage reduction bonuses from insignia on body armor do not stack; they are considered local upgrades and apply only to the part of the body protected by the piece of armor.
- Health and energy bonuses on armor stack, except for Runes of Vigor (which are non-stacking).
- Runes and inscriptions that provide condition reduction stack with each other. Runes that provide the same condition reduction do not stack.
- Health and energy bonuses on weapons stack (although: see the bug notes below).
- Runes and inscriptions that provide condition reduction stack with each other.
- Weapon upgrades that affect casting and recharge times stack, but are capped (see below).
 Skill effects
Most skill effects do not stack — the most recent or the most powerful application takes precedence.
- Effects that stack
- The beneficial effects of hex spells on different targets stack. For example, casting Life Siphon on two foes will return twice as much health to the caster as only one hex.
- Effects that do not stack
- Some skills will not stack with others of the same type: a character can only be affected by one stance, one preparation, one party bonus, one glyph, one weapon spell, and one form at a time. Activating a new one of the same type will override any existing ones.
- Animal companions can only be under the effects of a single Pet Attack buff.
- Characters can only hold one bundle at a time, so each new casting of an Item Spell causes the first urn to be dropped (triggering the when dropped effects).
- Armor rating bonuses from all skills are capped to a maximum of 25, however there are several bugs associated with this.
- Each Binding Ritual will result in the death of any allied spirit of the same type. Similarly, Nature Rituals will kill existing allied and enemy spirits of the same type.
 Non-additive stacking
- Blocking and missing stacks multiplicatively rather than additively. For example, a character enchanted with both Aegis and Guardian will have a 75% chance to block rather than a 100% chance.
 Effect caps
The game limits the maximum bonus or penalty that can be accrued from multiple sources; the effects stack, but only to a specified amount. In most cases, this cap can be exceeded by a single source.
|Chance to block or miss||100%|| Stacks multiplicatively. |
There are effects that prevent blocking or missing, but none that reduce the chances to block or miss.
|Health or energy regeneration||+10||-10||These caps also apply to single effects (not just multiple sources).|
|Recharge time||-50%||A single skill's effect can bypass this limit; item mods cannot stack beyond this limit.|
|Activation time||-25%||+150%||Fast Casting does not count toward this cap.|
|Armor rating||+25||60 AR||
|Maximum health||1||The minimum cap also apply to single effects (not just multiple sources).|
- The maximum number of maintained enchantments is limited only by your energy regeneration; you can never have your net energy regeneration at less than -10 (any maintained enchantments in excess of that cap will be lost). For example, a Monk can maintain a maximum of 14 enchantments.