Formulas : Magical resistance Miss Chance . When an offensive spell is cast , the target has two separate chances to resist the attack . First , there is a check based purely on the level difference between the caster and the target . This is referred to as the spell miss chance , and is affected by any Spell Hit Rating equipment that the caster is wearing . Talents that reduce the enemies ' chances to resist spells , such as Arcane Focus , are also taken into account by this check . If the target is of a significantly higher level , the spell will usually fail completely . If the target is significantly lower level , the spell will very rarely fail . This first check is why spell - casting players have such a hard time landing spells consistently on all monsters a few levels higher . In PvP combat , however , this is less of a factor ; a level 10 Mage can land polymorph on a level 70 player with some regularity . < br style = " clear : both ; " > " Note " : Level - based resistance ( not to be confused with level - based miss ) can play a factor in total resists . For every level that a mob has over the player , there is 8 resist ( believed ; the exact number may be higher ) added . For boss fights , this means there is 15 - 24 resistance added . This extra resistance means there will be partial resists on non - binary spells from the added resistance . However , this resistance has been shown to not apply to binary spells at all . This level based resistance cannot be reduced by any means , not even Spell Penetration . Magical Resistances . In addition to the miss chance , there is a roll based on the level of the caster and the resistance stat of the target . As with armor , the level of the target is not a factor in this roll . Average resistance may be no higher than 75 % . Of course , what it takes to reach 75 % average resistance depends on the spellcaster ' s level . One quirk here is that casters below level 20 are treated as if they were level 20 for purposes of calculating the resistance scaling here . So against a spellcaster of level 20 or below , it would take a resistance stat of 100 to get 75 % resistance ; level 30 would take 150 resistance ; level 50 would take 250 ; level 60 would take 300 ; and level 63 would take 315 . Why is it called " average resistance " ? For spells that have a non - damage effect such as slow , root , stun you ' ll either take the hit or avoid the hit altogether ; these are examples of binary spells . The average resistance is the chance you ' ll totally avoid the hit . Adding the word " average " is a little redundant in this case . However , when spells do only damage , it ' s not just a full hit or full miss situation . Pure damage spells can be resisted for 0 % , 25 % , 50 % , 75 % , or 100 % of their regular damage . Your average resistance can still be anywhere betweeen 0 % and 75 % . If your average resistance is maxed out , then there ' s a really good chance of having 75 % of the spell ' s damage be resisted . There ' s also a fairly good chance of having 100 % of the spell ' s damage be resisted , a slightly lower chance of 50 % of its damage being resisted , a small chances of only 25 % , or even 0 % of the damage being resisted . It ' s a weighted average . Visualize it as a bell curve around your average resistance . < br style = " clear : both ; " > Damage Absorbed . Unlike with armor , each extra point of magical resistance becomes more effective the more a character has . For example , going from 0 to 200 resistance halves the amount of damage a level 60 character takes , but to halve it again ( to 25 % ) the character only needs 100 more resistance . Similar to how melee damage reduction works , it is possible to calculate how much magical damage a character can take with a certain amount of health . This is the measure of how much damage a character can soak per point of health they have . Against a level 60 caster , a character with 200 resistance will resist 1000 damage for every 1000 damage they take , whereas with 240 resistance they will resist 1500 for every 1000 they take . So for an example , if there are two mages in a fight against Ragnaros ( boss level mobs are calculated as 3 levels higher then your current level ) , both with 3000 health , but one ( Mage A ) has just the 15 fire resist from mage armor , while the other ( mage B ) has 150 and is in a group with a paladin / shaman , so has an actual 210 resistance . Mage A will resist , on average , 111 damage before his 3k HP are gone and he dies . Mage B will resist , on average , 3000 damage before his 3k HP are gone and will likely have enough time to use a potion or something . < br style = " clear : both ; " >