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Lethality was introduced in League of Legends in Season 7 to replace flat armour penetration. It is one of the many stats in the game such as attack damage, ability power and bonus armor penetration which enhances your champion’s damage output. Assassins and certain burst damage ADCs usually build lethality items in-game to reduce enemy's armor. Supports like Pyke will also run lethality as it scales the damage on his abilities. Introducing lethality solved the problem of flat armour penetration allowing champions to snowball a little too much. Lethality is basically a scaled version of the old flat armour penetration.
How does Lethality work in League of Legends?
Lethality was introduced in the 2017 preseason of League of Legends to solve the issue of flat armor penetration putting out too much damage and allowing assassin champions like Zed to snowball. With lethality, enemy's armor is reduced by an amount through flat armor penetration. However, note that enemy armor cannot be reduced below 0. Instead of ignoring enemy armor by a flat amount (which is what flat armor penetration did before), lethality is a scaling effect that increases depending on your champion’s level.
Lethality grants flat armor penetration using the following formula:
Flat Armor Penetration = LETHALITY × (0.6 + 0.4 × level ÷ 18)
This means that at level 1, players will have at least 60 percent of the flat armor penetration any lethality item gives them. As your champion levels up, they will get 0.4 times more lethality per level, divided by 18. Lethality stacks additively and cannot reduce a target’s armor below zero. When effects stack additively, the total effect can be calculated simply by adding together each effect. For example, if you get +18 Lethality from Duskblade of Draktharr and +18 Lethality from Eclipse, your champion will now have a total of +36 Lethality. At level 10, using the Flat Armor Penetration formula given above, we can calculate lethality of your champion equipped with Duskblade of Draktharr and Eclipse as follows:
Flat Armor Penetration = 36 x (0.6 + 0.4 x 10 ÷ 18)
Thus the total flat armor penetration you get at level 10 with two lethality items is 29.599. Lethality is applied to the target after bonus armor penetration. If you have 20 flat armor penetration from lethality and 30 bonus armor penetration, the target’s damage calculation applies the 30 bonus armour penetration, before losing the flat armor penetration from lethality.
The following items currently grant lethality in League of Legends:
Apart from assassins which regularly use lethality items, some ADCs like Draven, Jhin, and Varus can take advantage of lethality to deal extra damage in the bottom lane. Most bottom lane ADCs and supports have a smaller amount of base armor. Lethality items can be used to punish enemies hard in trades as you transition to mid-game. While lethality is a great stat for certain champions, it is not very efficient against champions who build a lot of armor. Against champions with a lot of armor, going for bonus armor penetration is a better option compared to the scaled flat armor penetration derived from lethality items.
