How Does Magic Resist Work in League of Legends?

We’ve talked about how Armor works in League of Legends, so I only saw fit to explain Magic Resist as well. 

They’re more or less the same mechanically, and the formulae applied to Armor also will work on Magic Resist, so let’s get started. 

Magic Resist is a base stat in League of Legends, meaning that every Champion starts with a certain amount and gets more each level. All structures, monsters, and other units have Magic Resist as well (same goes for Armor). 

Magic Resist is increased by, other than leveling up, items, abilities, and runes. Like Armor, it stacks additively, meaning that values are combined rather than multiplied. This lets you stack Magic Resist sources on top of each other for as much as you can get. 

But how does it work?

Magic Resist reduces incoming Magic Damage by a percentage. The following formula calculates the reduced damage:

This formula is identical to how Armor is calculated. 

Therefore, we can conclude that at 25 MR, you’ll get a 20% reduction in Magic Damage. At 100, that value goes up to 50%, etc. 

For each point of Magic Resist, your HP grows by 1% in effectiveness. This means that your HP numerically remains the same but can withstand a lot more – making it effectively greater than what it actually is. 

A formula calculates effective health, like with Armor: 

From this, we conclude that, at 100 Magic Resist, a unit with 1000 HP will have 2000 effective HP, meaning that it will take 2000 Magic Damage to kill them, despite their HP saying otherwise. 

Reducing Magic Resist values below 0 will amplify incoming Magic Damage. At -25 Magic Resist, the enemy’s attacks will deal 20% increased damage. 

If you’ve read our Armor article, you’ll be familiar with how it is reduced. Similarly, Magic Damage is reduced as well. So, let’s take a look. 

With Armor, we’ve had Armor Penetration, Lethality, and Armor Reduction. Three distinctive categories, both in name and mechanically. 

With Magic Resist, however, we have Magic Penetration, Magic Penetration, and Magic Resistance Reduction. Yes, there are two different Magic Penetration mechanics that both have the same name.

 To avoid confusion, I will call one Percentage Penetration and the other Flat Penetration

Magic Resistance Reduction works exactly the same as Armor reduction does. It can reduce the target’s MR by either a flat or a percentual amount.

Flat MR Reduction stacks additively, meaning that reduction values can stack on top of each other and take you below 0 Magic Resist, at which point damage dealt to you will be increased. 

Percentual MR Reduction, though more potent against high MR enemies, stacks multiplicatively. This means that, despite having high values, it will never take you below 0, and the less MR you have, the less effective it is. 

 Multiplicative stacking means that if there are two percentual reduction values, they are calculated by multiplying rather than combining. For example, if you have 2 30% reduction sources, their combined strength would net a 51% MR Reduction, rather than 60. 

Flat Penetration is exceptionally simple – you ignore a flat amount of the target’s MR. That’s about it. If the value of the MR ignored is greater than the target’s total MR, you’ll deal bonus damage based on the calculations we’ve made above. Think of flat Penetration as flat reduction that isn’t applied but rather acts passively. 

Likewise, Percentual Penetration works like Percentual MR Reduction. It ignores a percentage of the target’s MR. But it has diminishing effects the lower the target’s MR is, so make sure to combine all of the above for maximum efficiency. 

The gold value of Magic Resist is 18, lower than Armor’s 20. Most Champions in the game will have a shallow base Magic Resist stat, even when they hit level 18. It scales poorly based on level, and items/other sources are necessary to defend yourself from those pesky AP Assassins. 


Defenses in League of Legends are the most vital thing to have when faced against high damage opponents. By the end of the game, everyone will be strong enough to deal massive damage, so keep your defenses in check to avoid getting completely obliterated by anyone that dares sneeze in your direction. 

These guides take time and effort to make, so leave feedback to help us improve them. Keep a keen eye out on our website for more League of Legends-related content such as lists, guides, and articles. 

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