Magic penetration (or spell penetration) is a champion statistic which allows the magic damage done from their abilities, enhanced attacks, etc. to ignore some or all of a target's magic resistance. All champions have 0 base magic penetration but can increase it with items, runes or abilities for a few champions. This cannot affect enemy magic resistance beyond 0 to deal bonus damage.

Magic resistance reduction is the effect of some items and champion abilities that temporarily reduces the magic resistance of one or more targets. This allows allies to benefit from the reduction of magic resistance. This can reduce magic resistance below 0, resulting in bonus damage (see Magic resistance).

## Order of calculations

Magic penetration and magic resistance reduction work exactly like armor penetration and armor reduction.

Magic penetration and magic resistance reduction are applied in the following order:

1. Flat magic resistance reduction
2. Percentage magic resistance reduction
3. Flat magic penetration
4. Percentage magic penetration

## Flat magic resistance reduction

Flat magic resistance reduction stacks additively.

Example: 20 magic resistance reduction reduces the target's magic resistance by 20, so a target with 30 magic resistance will be reduced to 10 magic resistance. (30 − 20 = 10)

Flat magic resistance reduction can reduce a target's magic resistance below zero. For example, if an enemy with 10 magic resistance has their magic resistance reduced by 25, the enemy will have −15 magic resistance.

## Percentage magic resistance reduction

The target's magic resistance is multiplied by a percentage (100% − the listed reduction). Percentage magic resistance reduction stacks multiplicatively. Percentage magic resistance reduction is ignored if the target's magic resistance is 0 or less.

Example: 20% magic resistance reduction multiplies the target's magic resistance to 80%, so a target with 30 magic resistance will be reduced to 24 magic resist. (30 × 0.8 = 24)

Percentage magic resistance reduction makes a bigger difference on targets with higher magic resistance. For instance, with 40% magic resistance reduction, a target with 200 magic resistance will lose 80 while a target with only 50 magic resistance will lose 20.

## Flat magic penetration

The target's magic resist is treated as being reduced by an amount for purposes of damage calculation, but cannot be reduced below 0. Flat magic penetration stacks additively.

Example: 20 magic penetration causes the target to take damage as if its magic resistance was 20 less, so a target with 30 magic resistance will be treated as though it had 10 for purposes of damage calculation (the target's actual magic resistance value will not change, however).

Because the target's actual magic resistance value does not change, anything else depending on that value also doesn't change.

## Percentage magic penetration

The target's magic resistance is treated as being multiplied by a percentage for purposes of damage calculation (100% − the listed penetration). Percentage magic resistance reduction stacks multiplicatively. Percentage magic penetration is ignored if the target's magic resistance is less than 0.

Example: 20% magic penetration causes the target to take damage as if its magic resistance was multiplied by 80%, so a target with 30 magic resistance will be treated as though it had 24 for purposes of damage calculation (the target's actual magic resistance value will not change, however).

Because the target's actual magic resistance value does not change, anything else depending on that value also doesn't change (e.g. ).

Percentage magic penetration makes a bigger difference on targets with higher magic resistance. For instance, with 40% magic penetration, a target with 200 magic resistance will be considered as having 80 less while a target with only 50 magic resistance will be considered as having 20 less.

## Examples

Given 20 flat magic resistance reduction and 30% magic resistance reduction, and the target is affected by 10 flat magic penetration and 40% magic penetration,

• Target A has 80 magic resistance.
1. The 80 is reduced to 60 by your 20 magic resistance reduction.
2. The 60 is reduced to 42 by your 30% magic resistance reduction.
3. Your magic penetration makes you ignore 10 of the remaining 42 magic resistance, 32 is left.
4. Your magic penetration makes you ignore 40% of the remaining 32 magic resistance, 19.2.
5. Target A takes damage as if it has 19.2 magic resistance.
• Target B has 18 magic resistance.
1. The 18 is reduced to −2 by your 20 magic resistance reduction.
2. The −2 is not affected by any further calculations because it is less than 0.
3. Target B takes damage as if it has −2 magic resistance.

## Increasing magic penetration

### Items

• : Unique passive: +20 magic penetration. +25 ability power, +200 health. 1485 gold.
• : +20 magic penetration. Unique passive: Enhanced Movement 2. 1100 gold.
• : Unique passive: +40% magic penetration. +70 ability power. 2295 gold.

### Champion abilities

Note: Only the magic penetration bonus effect of these abilities is shown here. To read more information on each of these abilities, follow the link on each of them.

• while active, grants him 16% / 22% / 28% / 34% / 40% magic penetration.

### Masteries

• Arcane Knowledge Arcane Knowledge: Your magical spells penetrate 10% of the target's magic resistance.

### Runes

• Insight runes provide flat magic penetration. Destruction runes provide flat armor penetration and magic penetration.

### Neutral buffs

• Crystal Scar's Aura grants every champion 5% magic penetration while playing on the Dominion game mode.

## Reducing magic resistance

### Items

• : Unique aura: Reduces the magic resistance of nearby enemy champions by 20. +70 ability power, +57 magic resistance. 2650 gold.
• : Unique passive: Your physical attacks shred your target doing 20 magic damage and reducing their magic resistance by 6. This debuff stacks up to 4 times and lasts for 8 seconds. +25 ability power, 50% attack speed. 1825 gold.

### Champion abilities

Note: Only the magic resistance reduction effects of these abilities are shown here. To read more information on each of these abilities, follow the link to each of them.

Flat magic reduction:

• passively makes his autoattacks reduce the magic resistance of enemies hit by Error: Parameter '3' is not accepted. for 3 seconds.
• passively reduces the magic resistance of nearby enemies by 10.
• , at rank 2 and above, reduces armor and magic resistance by 1 per hit for 2 seconds (effect stacks up to 50 times).
• reduces the magic resistance of the target by 5 / 10 / 15 / 20 / 25 for 4 seconds.
• reduces the magic resistance of all targets by 4 / 5 / 6 / 7 / 8 each second for 5 seconds.
• reduces the magic resistance of all targets by 12 / 15 / 18 / 21 / 24 magic resistance reduction for 5 seconds.
• reduces the magic resistance of all targets by 8 / 9 / 10 / 11 / 12 for 8 seconds (effect stacks up to 10 times).

Percentage magic reduction:

• steals magic resistance of the target by 15% / 20% / 25%, this amount is doubled over the next 6 seconds.
• grants his next auto attack to reduce the enemy's magic resist by 10% / 15% / 20% / 25% for 5 seconds.
• reduces the magic resistance of all targets affected by 15% for 5 seconds.
• allows her autoattacks against enemy champions reduces their magic resistance by 3% for 5 seconds (effect stacks up to 5 times).
• reduces the armor and magic resistance of enemies that step on the trap by 20% / 25% / 30% / 35% / 40% for 12 seconds.

### Summoner spells

• , when augmented by , reduces the target's magic resistance by 10 for its duration.

## Notes

• Magic penetration is a very valuable stat for casters. There are few sources for it and so Insight marks are very popular runes.
• Commonly only one of or is built depending on how much magic resistance the enemy team is using.
• provides greater benefit if targets have at least 50 magic resistance remaining after all magic resistance reduction and flat magic penetration is applied.
• Magic penetration not only affects all champion abilities that deal magic damage, but also affects magic damage items.
• The on-hit effect on items like benefit from magic penetration.
• The actives on items like benefit from magic penetration as well.