Magic resistance

Magic Resistance (MR) reduces the damage a champion receives from magical attacks. It reduces the damage of incoming magical attacks by a percentage. The total amount of Magic Resistance can be decreased by Magic Penetration. You can either gain Magic Resistance by Runes, Masteries or Items you buy.

At level 18, magic resistance ranges from and 's 30 MR (23% damage reduction), to the 54 MR of  (35% damage reduction).

Damage Reduction
This percentage of reduction is determined by the formula:
 * Damage Reduction Percent = 100 * (Effective MR) / (100 + ABS(Effective MR))

For example, a champion with 150 points of magic resistance would take (100 * 150) / (100 + 150) = 60% reduced damage from magical attacks, while a champion with -25 effective magic resistance would receive (100 * -25) / (100 + 25) = -20% reduced damage from magical attacks or, in other words, 20% increased damage from magical attacks. The effective magic resistance is determined by your personal magic resistance and the attacker's Magic Penetration.

|x|%29+from+-500+to+500 A graph of damage reduction (y) against total magic resistance (x).

Effective Health
Another relevant calculation is the amount of bonus effective health. This refers to the amount of health that would have to be added to be equivalent to the damage reduction. For example, if damage is reduced by 50%, essentially health has been doubled since it now takes double the damage to kill that target. The calculation for this percentage of bonus effective health is as follows (EFR = Effective MR):
 * Bonus Effective Health Percentage = (100 / (1.0 - (EFR / (100 + EFR)))) - 100
 * Bonus Effective Health Percentage = EFR (by simplifying the equation above)

|x|%29%29%29%29-100+from+0+to+1000 A graph of bonus effective health percent (y) against total magic resistance (x).

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% of the champion's HP. For example, 100 magic resist gives 50% damage reduction and so 100% more damage is required to kill the champion.

This table lists damage reduction and effective health bonuses granted by various levels of magic resistance. The effective health numbers are based on a champion that has 1000 HP. Note that the amount of bonus effective health gained is constant. Increasing MR from 0 to 10 gives 100 additional effective health. Increasing from 500 to 510 gives the same 100 additional effective health. No matter how much MR is present, the next 10 would provide 100 additional effective health. This is because magic resistance does not have diminishing returns. This can also be seen in the second graph linked above which is straight line showing the constant increase.

Items

 * +24 MR. 400 Gold.
 * +24 MR, +270 Health +18 Armor UNIQUE Aura: +12 Armor / +15 MR / +8 Damage to nearby allied champions. 1925 Gold.
 * +25 MR, UNIQUE Passive: Enhanced Movement 2. Reduces the duration of Movement inhibiting effects by 35%. 1200 Gold.
 * +30 MR, +40% Attack Speed UNIQUE Passive: Physical Attacks deal 42 bonus magic damage and remove up to 42 mana from the target. 2150 Gold.
 * +30 MR, +7.5 Mp5 UNIQUE Passive: Increases your Mana Regen by 1% per 1% Mana you're missing. 890 Gold.
 * +30 MR, +350 Mana +80 Ability Power +7% Movement Speed UNIQUE Passive: 100% chance when an ability is used that your next physical attack deals an additional 100% of your Ability Power in damage. This effect has a 2 second cooldown. 3470 Gold.
 * +30 MR, +35 Damage UNIQUE Passive: If you would take Magic Damage which would leave you at less than 30% of your Maximum Health, you first gain a shield which absorbs 300 Magic Damage for 4 seconds. 60 second cooldown. 1800 Gold.
 * +30 MR, +250 Health UNIQUE Passive: Reduces ability cooldowns by 10% and increases healing and regeneration by 15%. 1550 Gold.
 * +38 MR, +68 Armor UNIQUE Passive: Revives your Champion upon death, restoring 750 Health and 375 Mana. This effect can only occur once every 5 minutes. 2600 Gold.
 * +48 MR. 740 Gold.
 * +50 MR, +375 Health +375 Mana UNIQUE Passive: Blocks one negative spell every 45 seconds. 2715 Gold.
 * +56 MR, Active: Removes all debuffs from your champion. 105 second cooldown. 1440 Gold.
 * +57 MR, +70 Ability Power UNIQUE Aura: Reduces the Magic Resist of nearby enemy champions by 20. 2650 Gold.
 * +76 MR, +40 Hp5 +8% Movement Speed UNIQUE Passive: Restores 0.35% of your champion's health every second. 2610 Gold.

Champion Abilities

 * lays down a cover of smoke for 8 seconds where she gains 10/20/30/40/50 magic resistance while in.
 * 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 3.5 seconds.
 * increases his magic resistance by 0.5 per kill with a maximum of 5/10/15/20/25.
 * increases his magic resistance by 20/35/50 + his Dodge Percentage for 5/6.5/8 seconds.
 * increases his magic reistance by 10/20/30/40/50 for 4 seconds.
 * 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
 * increases his magic resistance by 50/75/100/125/150 for 6 seconds.
 * 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 25 (+7/10/13 for each enemy champion hit) for 8 seconds.

Masteries

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

Runes

 * Shielding and Warding runes may also increase magic resistance.

Champions MR gain
There are champions who gain and not gain Magic Resistance during leveling.

Those who do not gain
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Those who do gain
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Updates
Due to recent updates this article may not be up-to-date. It was last updated during Patch V1.0.0.107. If there is a new version out, please check the data frequently.