Stacking

Stacking has two meanings, the one being used can be deduced from the context. Effect stacking occurs when a single effect is applied more than once to a target. Stats stacking occurs when stats are modified by multiple effects.

Effect stacking

Champion abilities, summoner spells, items, and buffs often apply effects to characters. Different effects always stack with each other. However, if the same effect is applied several times to the same unit, sometimes it stacks and sometimes it does not stack.

When a non-stacking effect is applied to a target that already has the effect, the effect's duration is reset to the duration of the most recent application.

When a stacking effect is applied to a target that already has the effect:

• The number of stacks of that effect increases by one, unless the maximum number of stacks has been reached. For example,  Jinx's Rev'd up stacks up to 3 times.
• The duration of all stacks is reset to the duration of the most recent application.

Example: If Jinx has 1 stack of Rev'd up with 1 second left and gets another, the duration of the first stack resets to the full 2.5 seconds.

Some stacking effects are just counters building up to a different effect (e.g. Caitlyn's Headshot). Most effects, though, have their potency multiplied by the number of stacks.

Example: If Ezreal has 5 stacks of Rising Spell Force, his attack speed is increased by 50% = 5 stacks × 10%.

Aura stacking

Aura effects don't stack with themselves: If champion A and champion B are generating the same aura, and champion C is affected by both auras, champion C receives the effect of these auras only once. However, for the purposes of stacking, if the aura has two different effects based on if the target is the user or somebody else, then the auras stack with each other. A unit receives the aura effect from the aura they are creating, but also the effect from the aura created by their ally.

Champion statistic stacking

Some statistics can be modified by multiple effects. A stat may stack additively or multiplicatively

Stacks additively

When effects stack additively, the cumulative effect can be calculated simply by adding together each effect.

+100 health   +100 health

⇨

+200 health

Example: if your champion has two items granting +100 health each, your champion has 200 bonus health.

Effects that stack additively

•  Ability haste
•  Ability power
•  Armor
•  Armor penetration, flat
•  Armor reduction, flat
•  Attack damage
•  Attack speed bonuses (increases and decreases) ¹
•  Critical strike chance
•  Critical strike damage
• Damage amplification
•  Heal and shield power
•  Health
•  Health regeneration
•  Life steal
•  Magic penetration, flat
•  Magic resistance
•  Magic resistance reduction, flat
•  Mana
•  Mana regeneration
•  Omnivamp
•  Physical vamp
• Size

¹ Attack speed has an upper and a lower limit.

Stacks multiplicatively

When effects stack multiplicatively, the cumulative effect can be calculated by multiplying the effects together. Note that the game interface rounds champion statistics, so what is shown in-game may be slightly different than what is calculated.

It is important to understand that most champion statistics that stack multiplicatively are displayed as the opposite of the actual numbers that are multiplied. For example, 10% damage reduction means 90% damage taken, 25% damage reduction means 75% damage taken, etc.

10% damage reduction   10% damage reduction	⇨	19% damage reduction
↓		↑
Damage ×0.9 × Damage ×0.9	=	Damage ×0.81

Example: If your champion has armor granting 10% damage reduction and an item granting 10% damage reduction, you multiply the damage factors—0.9 and 0.9—to get 0.81, which means your champion has 19% damage reduction (against physical damage).

Effects that stack multiplicatively

• Cripples
• Damage reduction (with exceptions) ¹
•  Armor penetration, percent
•  Armor reduction, percent
•  Magic penetration, percent
•  Magic resistance reduction, percent
• Slow resist

¹ Armor and magic resistance each contribute a percentage value to the larger category of "damage reduction." Calculate the final percentage of each before combining with other sources of damage reduction. Some damage reduction status effects also stack additively due to modifying the same effect/statistic internally.

Special stacking

Please visit the respective articles for details on these statistics' stacking:

•  Movement speed
• Tenacity
• Finally, all sources of named item effects cannot stack with each other.