Order of calculations
When attacking, armor penetration and armor reduction are considered in the following order :
- Armor reduction, flat
- Armor reduction, percentage
- Armor penetration, percentage
- Armor penetration, flat
Flat armor reduction
The target's armor is reduced by an amount. Flat armor reduction stacks additively.
- Example: 20 armor reduction reduces the target's armor by 20, so a target with 30 armor will be reduced to 10 armor (30 − 20 = 10).
Flat armor reduction can reduce a target's armor below zero. For example, if an enemy with 10 armor has their armor reduced by 25, the enemy will have −15 armor.
Percentage armor reduction
The target's armor is multiplied by a percentage (100% − the listed reduction). Percentage armor reduction stacks multiplicatively and is ignored if the target's armor is 0 or less.
- Example: 20% armor reduction multiplies the target's armor to 80%, so a target with 30 armor will be reduced to 24 armor (30 × 0.8 = 24).
Percentage armor reduction makes a bigger difference on targets with higher armor. For instance, with 40% armor reduction, a target with 200 armor will lose 80 while a target with only 50 armor will lose 20.
Percentage armor penetration
The target's armor is treated as being multiplied by a percentage for purposes of damage calculation (100% − the listed penetration). Percentage armor penetration stacks multiplicatively and is ignored if the target's armor is 0 or less.
- Example: 20% armor penetration causes the target to take damage as if its armor was multiplied by 80%, so a target with 30 armor will be treated as though it had 24 for purposes of damage calculation (the target's actual armor value will not change, however).
Percentage armor penetration makes a bigger difference on targets with higher armor. For instance, with 40% armor penetration, a target with 200 armor will be considered as having 80 less while a target with only 50 armor will be considered as having 20 less.
Due to the order of operations, percentage armor penetration negatively interacts with armor reduction.
Last Whisper is a special case in that it is a percentage bonus armor penetration. Since armor reduction is subtracted from bonus armor first, the interaction with especially percentage armor reduction is even worse. However, percentage armor penetration and percentage bonus armor penetration stack additively as opposed to different sources of percentage armor penetration stacking multiplicatively, hence they are synergistic with each other.
The interaction between different sources of bonus armor penetration is still unexplained. Currently, the only two sources of this stat in the game are Yasuo's Last Breath and Last Whisper, and preliminary tests of this combination neither fall in accordance to multiplicative nor additive stacking, but behave weirdly.
Flat armor penetration
The target's armor is treated as being reduced by an amount for purposes of damage calculation, but cannot be reduced below 0. Flat armor penetration stacks additively.
- Example: 20 armor penetration causes the target to take damage as if its armor was 20 less, so a target with 30 armor will be treated as though it had 10 for purposes of damage calculation (the target's actual armor value will not change, however).
Given 20 flat armor reduction and 30% armor reduction, and the target is affected by 10 flat armor penetration and 35% armor penetration,
- Target A has 80 armor.
- The 80 is reduced to 60 by the 20 armor reduction.
- The 60 is reduced to 42 by the 30% armor reduction.
- The 42 is considered to be 27.3 by the 35% armor penetration.
- The 27.3 is considered to be 17.3 by the 10 armor penetration.
- Target A takes damage as if it has 17.3 armor.
- Target B has 18 armor.
- The 18 is reduced to −2 by the 20 armor reduction.
- The −2 is not affected by any further calculations because it is less than 0.
- Target B takes damage as if it has −2 armor.
Increasing armor penetration
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- Unique Passive – Duskblade of Draktharr: +10 armor penetration :
- Unique Passive – Last Whisper: +30% bonus armor penetration :
- Unique Passive – Last Whisper: +45% bonus armor penetration
. +40 attack damage. Unique Passive – Giant Slayer: Grants up to +15% physical damage against enemy champions with greater maximum health than you (+1.5% damage per 50 health difference, maxing at 500 health difference).
- +10 armor penetration
. +55 attack damage, +50 magic resist. Unique Passive – Lifeline: Upon taking magic damage that would reduce health below 30%, grants a shield that absorbs 300 + (100% bonus MR) magic damage for 5 seconds (90 second cooldown). Unique Passive – Lifegrip: When Lifeline triggers, gain +25% attack speed, +10% spell vamp, and +10% life steal until out of combat.
- Unique Passive – Last Whisper: +45% bonus armor penetration :
- Unique Passive: +10 armor penetration :
- Unique Passive: +20 armor penetration :
Note: Only the armor penetration effect of these abilities is shown here, to read more information on each of these abilities, follow the link on each of them.
- Darius's Apprehend passively grants him 5 / 10 / 15 / 20 / 25% armor penetration.
- Gangplank's Powder Keg ignore 40% of targets' armor.
- Yasuo's Last Breath upon activation grants him 50% penetration to bonus armor.
- Battering Blows grants 1.4 / 2.8 / 4.2 / 5.6 / 7% armor penetration.
- Precision grants 0.6 / 1.2 / 1.8 / 2.4 / 3 flat + 0.06 / 0.12 / 0.18 / 0.24 / 0.3 per level armor penetration.
|Name||Type||Tier 1 (Lesser)||Tier 2 (Normal)||Tier 3 (Greater)|
|Armor Penetration||Mark|| 0.72
(Armor Penetration / Magic Penetration)
|Mark||X||X|| 0.9 armor penetration|
0.62 magic penetration
|Quintessence||X||X|| 1.79 armor penetration|
1.4 magic penetration
- Unique Passive: Dealing physical damage to an enemy champion Cleaves them, reducing their armor by 5% for 6 seconds (stacks up to 6 times, up to 30%)
. +300 health, +55 attack damage, +20% cooldown reduction. Unique Passive – Rage: Dealing physical damage grants 20 movement speed for 2 seconds. Assists or kills on Cleaved enemy champions or kills on any unit grant 60 movement speed for 2 seconds instead. This movement speed bonus is halved for ranged champions.
Note: Only the armor reduction effect of these abilities is shown here, to read more information on each of these abilities, follow the link on each of them.
- Jarvan IV's Dragon Strike reduces the armor of all enemies hit by 10 / 14 / 18 / 22 / 26% for 3 seconds.
- Jayce's Transform: Mercury Cannon reduces the armor and magic resistance of the enemy hit by his first attack after cast, by 10 / 15 / 20 / 25% for 5 seconds
- Kayle's Holy Fervor reduces the armor of enemies hit by her autoattacks by 3% for 5 seconds. This debuff stacks up to 5 times.
- Kog'Maw's Caustic Spittle reduces the target's armor and magic resistance by 12 / 16 / 20 / 24 / 28% for 4 seconds.
- Renekton's Slice and Dice, when empowered by having more than 50 Fury, Dice will reduce the armor of all enemies hit by 15 / 20 / 25 / 30 / 35% for 4 seconds.
- Sion's Roar of the Slayer reduces the armor of the first target hit by 20% for 2.5 seconds.
- Trundle's Subjugate reduces the armor of his target by 20% and gains for the same amount. This amount is doubled over the next 4 seconds. The armor reduction lasts for another 4 seconds after the drain completes.
- Urgot's Noxian Corrosive Charge reduces the armor of all enemies hit by 12 / 14 / 16 / 18 / 20% for 5 seconds.
- Vi's Denting Blows reduces the target's armor by 20% for 4 seconds after every third consecutive hit.
- Wukong's Crushing Blow reduces the armor of the target hit by 10 / 15 / 20 / 25 / 30% for 3 seconds.
- Xin Zhao's Challenge reduces the armor of targets hit by his basic attacks or Audacious Charge by 15% for 3 seconds. Only one target may be challenged at a given time.
- Corki's Gatling Gun fires automatically every half second, reducing enemies armor with each hit by 1 / 2 / 3 / 4 / 5 for 2 seconds up to a maximum of 8 stacks (8 / 16 / 24 / 32 / 40).
- Nasus's Spirit Fire reduces the armor of all enemies in the area by 20 / 25 / 30 / 35 / 40 for the time they are on it plus 1 second.
- Rammus's Puncturing Taunt reduces the target's armor by 10 / 15 / 20 / 25 / 30 for 1.25 / 1.5 / 1.75 / 2 / 2.25 seconds.
- Taric's Shatter reduces the armor of all enemies hit by its activation damage by 5 / 10 / 15 / 20 / 25 (+ 5% armor) for 4 seconds.
- Armor penetration is a very valuable stat for physical damage dealing champions. There are few sources for it, so armor penetration Marks and Quintessences are very popular runes.
- Armor penetration benefits all sources of physical damage including all champion abilities that deal physical damage.
- For example, Xin Zhao's Crescent Sweep will benefit from armor penetration as it deals physical damage, however his Audacious Charge will not benefit from armor penetration as it deals magical damage.
- The items that deal on-hit physical damage: , , , , and , will also benefit from armor penetration.
- Turrets are also subjected to armor penetration effects.
- ↑ If I technically had 100% armor reduction on an enemy... at League of Legend