 Lethality redirects here. For the 2013 Mastery, see Lethality.
Armor penetration is a champion statistic that reduces the effective armor of the target (vs. the champion with armor penetration).
Example: 10% armor penetration causes a target to take physical damage as though they had 10% less armor; 10% armor penetration is equivalent to fighting a target with 10% less armor.
The difference between armor penetration and armor reduction is that armor reduction can reduce armor below zero and affects any source of physical damage. The effects of armor penetration, on the other hand, are ignored once the target's effective armor drops to 0, and only the source of the armor penetration deals increased damage.
Lethality is a champion statistic introduced in season 2017 that is converted to flat armor penetration at a rate that increases based on your level, see formula below^{[1]}.
All champions have 0 base armor penetration, but it can be increased with items, runes, and some champion abilities.
Gold Value
Order of calculations
When attacking, armor penetration and armor reduction are considered in the following order:^{[2]}
 Armor reduction, flat
 Armor reduction, percentage
 Armor penetration, percentage
 Lethality
Note: Base armor and bonus armor are calculated separately.
Flat armor reduction
The target's armor is reduced by an amount. Flat armor reduction from different sources stacks additively and is distributed proportionally between base armor and bonus armor.
 Example: 30 armor reduction against a 20 base armor and 40 bonus armor target will reduce base armor by 10 and bonus armor by 20, so the target will be reduced to 30 armor ((20 − 10) + (40 − 20) = 30).
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). Applies to both base and bonus armor. Percentage armor reduction stacks multiplicatively and is ignored if the target's armor is 0 or less.
 Example: 30% armor reduction multiplies the target's armor to 70%, so a target with 20 base armor and 40 bonus armor will be reduced to 42 armor ((20 × 0.7) + (40 × 0.7) = 42).
Percentage armor reduction reduces more armor 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. The increase in damage on the other hand isn't that big, because of the diminish return of armor at higher levels. On a target with 50 armor the actual physical damage will be increased by around 15%, where as the physical damage on targets with 200 armor by around 36% when having 40% armor reduction.
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: 30% armor penetration causes the target to take damage as if its armor was multiplied by 70%, so a target with 20 base armor and 40 bonus armor will be treated as though it had 42 for purposes of damage (the target's actual armor value will not change, however) ((20 × 0.7) + (40 × 0.7) = 42).
Because the target's actual armor value does not change, anything else depending on that value also doesn't change (e.g.
).Percentage armor penetration reduces more armor 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. The increase in damage on the other hand isn't that big, because of the diminish return of armor at higher levels. On a target with 50 armor the actual physical damage will be increased by around 15%, where as the physical damage on targets with 200 armor by around 36% when using 40% armor penetration.
Percentage bonus armor penetration
Percentage armor penetration that applies only to bonus armor.
 Example: 30% bonus armor penetration multiplies the target's bonus armor to 70% without affecting base armor, so a target with 20 base armor and 40 bonus armor will be treated as though it had 48 for purposes of damage calculation (the target's actual armor value will not change, however). (20 + (40 × 0.7) = 48).
 If the player has multiple sources of percentage bonus penetration, they stack multiplicatively:
 Example: 10% armor penetration and 30% bonus armor penetration. (20 × 0.9)) + (40 × 0.7 × 0.9)) = 43.2).
Because the target's actual armor value does not change, anything else depending on that value also doesn't change (e.g.
).Percentage bonus armor penetration makes a big difference on targets who build armor items, but will do nothing against base armor.
Lethality
Lethality is a new statistic introduced in Season 2017 to replace flat armor penetration. It grants flat armor penetration using the following formula:
 Flat Armor Penetration = Lethality × (0.6 + 0.4 × level ÷ 18)
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 1: 20 lethality causes a target(level 18) 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).
Because the target's actual armor value does not change, anything else depending on that value also doesn't change (e.g.
).Examples
Given 30 flat armor reduction and 30% armor reduction, and the target is affected by 10 flat armor penetration and 45% bonus armor penetration,
 Target A has 300 armor (100 base and 200 bonus armor).
 The 300 is reduced to 270 (90 base and 180 bonus armor) by the 30 armor reduction.
 The 270 is reduced to 189 (63 base and 126 bonus armor) by the 30% armor reduction.
 The 189 is considered to be 132.3 (63 base and 69.3 bonus armor) by the 45% bonus armor penetration.
 The 132.3 is considered to be 122.3 by the 10 armor penetration.
 Target A takes damage as if it has 122.3 armor.
 Target B has 18 armor.
 The 18 is reduced to −12 by the 30 armor reduction.
 The −12 is not affected by any further calculations because it is less than 0.
 Target B takes damage as if it has −12 armor.
Lethality as scaling
The following have their stats improved based on the amount of lethality acquired:
Champion abilities
 , , and
Increasing lethality
Champion abilities
Items
Runes
Increasing armor penetration
Champion abilities
 bonus armor) (affects only
Items
Reducing armor
Champion abilities
 Percentage Reduction
 Flat Reduction
Items
Monsters
 Flat Reduction
Notes
 Armor penetration is a very valuable stat for physical damage dealing champions.
 Armor penetration benefits all sources of physical damage including all champion abilities that deal physical damage.
 For example, will benefit from armor penetration as it deals physical damage, however his will not benefit from armor penetration as it deals magical damage.
 The items that deal onhit physical damage: , , , , and , will also benefit from armor penetration.
 Turrets and have 30% armor penetration.
 Turrets are affected by percentage armor penetration and lethality.
Trivia
 The maximum amount of lethality any champion can obtain is 103:
 Runes:
  7
 Items (sorted in order from highest to least lethality):
 1  25
 1  21
 1  18 (including passive)
 1  12
 1  10
 1  10
 Relevant mathematics:
 Items and runes =
 The highest amount obtainable is with
 103 + (lethality fully leveled) = 115 lethality
:
+ + + + + + = 103 lethality
 The highest amount obtainable is with
 Items and runes =
 On Nexus Blitz, the maximum amount of lethality any champion can obtain becomes 119:

 This is further increased to 131 lethality with when his , which grants 12 lethality when fully leveled, is included in the equation, effectively becoming the highest amount obtainable in the game.
+ + + + + + = 119 lethality

 The highest amount of percentage armor penetration obtainable is with

 Relevant mathematics:
 (1  0.35) × (1  0.35) = 0.4225
 1  0.4225 = 0.5775 = 57.75%
 (1  0.35) × (1  0.35) = 0.4225
at max rank (35%) paired with (35%) = 57.75% armor penetration
 Relevant mathematics:
:

References
Offensive  Ability power · Attack damage · Attack speed · Critical strike chance · Critical strike damage · Armor penetration · Magic penetration · Life steal · Spell vamp · True damage 

Defensive  Heal and shield power · Health · Health regeneration · Armor · Magic resistance · Tenacity · Slow resist 
Utility  Cooldown reduction · Energy · Energy regeneration · Mana · Mana regeneration 
Other  Experience · Gold generation · Movement speed · Range 