Magic resistance

Magic resistance (MR) reduces the magic damage a champion receives by a calculated percentage. A portion of an enemy's magic resistance can be ignored with magic penetration. You gain magic resistance from runes, masteries, items, and abilities, and some champions naturally gain it as they level.

All champions begin with 30 base magic resistance. No ranged champions save gain magic resistance per level, but many melee champions do, with 52.5 being the maximum magic resistance possible without items, runes, or masteries.

Damage reduction
Incoming magic damage is multiplied by a specific factor based on your Magic Resistance:
 * Damage multiplier100(100magic resistance) when magic resistance ≥ 0

Example: 25 magic resistance &rarr; damage multiplier100(10025)1001250.8, so incoming magic damage is reduced by 20 percent.

It is important to note that the amount of health you have is irrelevant to the effectiveness of magic resistance. For example: 25 magic resistance always reduces magic damage by 20 percent.

A graph showing the damage multiplier decrease as magic resistance increases.

Effective health
You can also view magic resistance as a sort of "extra health," where each point of magic resistance gives your champion 1 percent additional health against magic damage. For example: if your champion has 100 magic resistance, you could calculate the damage multiplier as being 0.5, or that your champion has 100 percent more health against magic damage. No matter how you view it, the end result is that your champion lasts twice as long against magic damage.

This extra health, combined with your normal health, is called effective health. A champion's effective health against magic damage can be calculated as:
 * Effective healthhealth(100magic resistance)100 when magic resistance ≥ 0

Example: 500 health and 25 magic resistance &rarr; effective health500(10025)100500125100 = 5001.25625.

A graph showing effective health increase as magic resistance increases. (Effective health represented as a multiplier of base health.)

Negative magic resistance
Effects that reduce magic resistance (not to be confused with Magic Penetration) can bring magic resistance into negative values, causing magic damage to be more effective. Negative magic resistance does not follow the same formula as positive magic resistance, however (see the next section for why). Negative magic resistance &minus;x increases incoming magic damage by the same percentage that positive magic resistance x reduces incoming magic damage by. The damage multiplier is calculated as follows:
 * Damage Multiplier2100(100MR) when magic resistance ≤ 0

Example: &minus;15 magic resistance &rarr; damage multiplier2100(100(&minus;15))2100(115) ≈ 20.87 ≈ 1.13, so incoming magic damage is increased by ~13 percent.

As a result, the formula for effective health is different as well:
 * Effective health0.525(magic resistance50) when magic resistance ≤ 0

Reasoning
If the original damage multiplier formula is followed back into negative numbers, the multiplier begins to increase dramatically, literally approaching infinity when magic resistance reaches &minus;100 and being negative when magic resistance is less than that. In order to keep this from happening, a different formula is used that does not have such an asymptote; with this new formula having &minus;100 magic resistance adds 50 percent magic damage instead of making it infinite, and the damage increase softly maxes out at 100 percent damage.

Diminishing returns
Magic resistance does not have diminishing returns from an effective health perspective; each point of magic resistance increases the amount of magic damage required to kill the champion by 1 percent of the champion's health. For example: 100 magic resistance reduces magic damage by 50 percent, so 100 percent more magic damage is required to kill the champion.

This table lists damage reduction and effective health bonuses granted by various magic resistance levels. The effective health entries are based on a champion that has 1000 health. Note that the effective health increase is constant as magic resistance increases; increasing magic resistance from 0 to 10 gives 100 additional effective health, and increasing from 500 to 510 gives the same 100 additional effective health. No matter how much magic resistance is present, the next 10 points provide 100 additional effective health. This can also be seen in the graph linked above (see section: Effective health, showing a straight line that represents the constant increase.)

Champion abilities

 * lays down a cover of smoke for 8 seconds where she gains 10/20/30/40/50 magic resistance while inside.
 * increases her magic resistance by 10/20/30/40/50 for 15 seconds.
 * increases an allied champion's magic resistance by 30/45/60/75/90 for 4 seconds.
 * increases his magic resistance by 0.5 per kill with a maximum of 25.
 * increases his magic resistance by every second he remains in combat. This bonus stacks up to 10 times. Graves is considered in combat if he has dealt or received damage in the last 3 seconds.
 * increases his magic resistance by 20/35/50 (+ his dodge percentage) for 5/6.5/8 seconds.
 * increases his magic resistance by 10/20/30/40/50 for 4 seconds.
 * increases her magic resistance by 30/40/50/60/70 for 3 seconds. The duration of the buff is doubled if any enemies are damaged by the ability.
 * increases his magic resistance by 100/150/200/250/300 for 5 seconds.
 * increases an allied unit's magic resistance by 10/15/20/25/30 for 6 seconds.
 * grants her 10/20/30 magic resistance while in Cougar form.
 * increases an allied champion's magic resistance by 10/15/20/25/30 as long as the ball is attached to it.
 * increases his magic resistance by 50/75/100/125/150 for 6 seconds.
 * passively increases her magic resistance by 15/20/25. This bonus is doubled while she is in Dragon Form.
 * increases his magic resistance by 35/50/65 for 25 seconds.
 * increases nearby allied champions' magic resistance by 8/11/13/17/20 while active.
 * increases nearby allied champions' magic resistance by 16.
 * increases his magic resistance by 15/20/25% of the target enemy's magic resistance, and doubles the amount over the next 6 seconds.
 * increases his magic resistance by 80/105/130 for 4 seconds.
 * grants him 4/6/8 magic resistance for each nearby enemy champion.
 * increases his magic resistance by 25 (+7/10/13 for each enemy champion hit) for 8 seconds.

Masteries

 * increases your champion's magic resistance by 2/4/6.

Runes

 * and runes may also increase magic resistance.

Ways to reduce magic resistance
Note that magic penetration and magic resistance reduction are different. See the below article for more information.