How Armor Penetration, Magic Pen and Lethality Work in LoL

Penetration is the most commonly misunderstood stat in the game, and the order it applies in decides whether your third item is worth buying.

The short version: reduction happens before penetration, and percentage happens before flat. Everything else follows from those two rules.

LEAGUE OF LEGENDS

PENETRATION EXPLAINED

UPDATED AUGUST 2026

Penetration is the most commonly misunderstood stat in the game, and the order it applies in decides whether your third item is worth buying.

The short version: reduction happens before penetration, and percentage happens before flat. Everything else follows from those two rules.

The order of operations

Armor and magic resist work identically here. Both run through the same four steps, in this order:

Step	What applies	Example source
1	Flat reduction	Champion abilities, mostly
2	Percent reduction	Black Cleaver
3	Percent penetration	Lord Dominik's Regards, Void Staff
4	Flat penetration	Lethality items, Sorcerer's Shoes

Reduction and penetration are not the same thing

This is the distinction that actually matters, and it is why the order above exists:

• Reduction can push a resist below zero. If a target has 20 armor and you apply 30 armor reduction, they are sitting at negative 10 and taking bonus damage.
• Penetration cannot. It never takes anyone below zero. It only ever claws back toward zero.
• Percent penetration is ignored entirely if the target is already at zero or less. Multiplying a negative resist would help them, so the game simply skips the step.

Because reduction is applied first, it is also strictly better per point than penetration against low-resist targets, and it benefits your whole team rather than just you.

Armor penetration items in Patch 26.15

Item	Type	Amount
Lord Dominik's Regards	Percent armor pen	35%
Serylda's Grudge	Percent armor pen	35%
Mortal Reminder	Percent armor pen	30%
Last Whisper	Percent armor pen	18%
Bastionbreaker	Lethality	22
Youmuu's Ghostblade	Lethality	18
Umbral Glaive	Lethality	18
Axiom Arc	Lethality	18
Black Cleaver	Percent armor reduction	Applies at step 2

Magic penetration items in Patch 26.15

Item	Type	Amount
Void Staff	Percent magic pen	40%
Cryptbloom	Percent magic pen	30%
Blighting Jewel	Percent magic pen	13%
Spellslinger's Shoes	Flat and percent	18 flat, 8%
Shadowflame	Flat magic pen	15
Stormsurge	Flat magic pen	15
Sorcerer's Shoes	Flat magic pen	12

Lethality no longer scales with level. A lot of guides still quote the old formula, Lethality × (0.6 + 0.4 × level / 18). That was removed in Patch 14.1. Since then, 1 Lethality is 1 flat armor penetration at every level, so 18 Lethality ignores 18 armor whether you are level 3 or level 18. If a site is still showing you that formula, it has not been updated in two years.

Worked examples

Magic: Void Staff plus Sorcerer's Shoes into 100 MR

Percent first, then flat. 100 × 0.60 = 60, then 60 minus 12 = 48 effective magic resist.

Damage taken goes from 100 / (100 + 100) = 50% up to 100 / (100 + 48) = 67.6%. That is roughly 35% more damage.

Physical: Lord Dominik's plus Youmuu's into 100 armor

100 × 0.65 = 65, then 65 minus 18 = 47 effective armor.

Damage taken goes from 50% up to 100 / (100 + 47) = 68%. Again roughly 36% more damage.

Why percent scales and flat does not

Flat penetration is worth the most against low-resist targets and gets progressively worse as they build armor. Percent penetration does the opposite. That is the entire reason lethality is an early game and squishy-killing stat, and why the Last Whisper line exists as a late game answer to tanks.

What Phreak said back in 2013

This post originally covered a forum explanation from RiotPhreak. The item names are long gone, but the underlying logic is unchanged, so it is worth keeping as a record:

First, % penetration works first. So if I have a Void Staff/Last Whisper, I pretend your MR/Armor is only 65% of what it really is. Then I factor in things like Brutalizer/Sorc Shoes/Haunting Guise. Those things work additively.

Note that penetration can only go so far. What I mean is that, if you have exactly 100 flat magic pen, it will only give you at most 100% bonus damage (your opponent has 100 MR). If your opponents have any more or less than 100 magic resist, you will get slightly lower returns.

RiotPhreak, 2013. The original League forums have since been retired, so the source link no longer resolves.

Where to go next

Penetration only matters once you know what you are building it on. For the champions worth picking this patch, see the solo queue tier list. For the other half of the rune page, read our stat shards guide.

Still have a penetration question? Comment below!