Casting Speed Casting speed is the time it takes for a spell to take effect . Some spells are " instant " and take effect immediately , while some spells are " channeled " and have their effects occur over the duration of the cast . Others take effect after a specific " cast time " , with typically more powerful spells having longer cast times . Regardless of the type of spell , there is a global cooldown that prevents rapidfire spellcasting even with " instant " spells . Various factors can reduce a spell ' s " cast time " from its base " cast time " ( specified in the spell ) : Certain debuffs , such as Curse of Tongues or Mind - numbing Poison , can decrease your casting speed . Casting speed calculation . % Spell Haste at level 70 = ( Haste Rating / 15 . 77 ) % Spell Haste at level 80 = ( Haste Rating / 32 . 79 ) New Casting Time = Base Casting Time / ( 1 + ( % Spell Haste / 100 ) ) Note that " base casting time " is after talents . For example , a warlock ' s shadow bolt is 3 . 0 " base cast time " under normal usage of the term " base cast time " . However , for the purpose of this formula , you should use the improved cast time from your talents ( 2 . 5 cast time , in this example ) if you have that talent , or the formula will not give the correct result . Essentially , 1 % haste allows a player to cast 1 additional spell in the time it would normally take to cast 100 spells . If the spell is a 3 second cast , that means one can theoretically cast 101 spells in 300 seconds , or 2 . 97 seconds per spell . To determine the amount of time taken to cast a given sequence of spells , the reverse formula can be used , where Base Casting Time is the sum of all the spells in the given sequence : Haste Rating needed at level 70 = ( ( Base Cast Time / Desired Cast Time ) - 1 ) * 15 . 77 * 100 Haste Rating needed at level 80 = ( ( Base Cast Time / Desired Cast Time ) - 1 ) * 32 . 79 * 100 Example : I am a level 70 mage , and I want my Fireball ( 3s ) , Fireball ( 3s ) , Scorch ( 1 . 5s ) cast chain to take 6 . 5 seconds . Therefore , a [ 1577 * ( ( 7 . 5 / 6 . 5 ) - 1 ) = ~ 243 Haste Rating ] is required . Note : Blizz ard rounds to 4 significant digits . Pre - 3 . 0 . Haste Rating used to be split into " Haste Rating " ( which only affected attack speed ) and " Spell Haste Rating " ( which only affected spell casting speed ) . The two have been unified as of patch 3 . 0 . 2 into one universal Haste Rating stat . All gear which used to have Spell Haste Rating now has an equal amount of Haste Rating . Improving casting speed . Various sources that improve casting speed are listed on the Casting Speed improving items page . Note : Haste rating stacks additively with itself but haste stacks multiplicatively . That means that if you have 158 haste rating , you will have + 10 % haste , no matter how many sources and items that haste rating comes from . If you then use troll Berserking for + 30 % haste , you would have 110 % * 130 % = 143 % haste . Spell Pushback . Recieving a damaging attack while casting will " push back " the cast by 0 . 5 seconds . This is visible from the casting bar flinching away from completion . Only the first two attacks will cause pushback , in effect lengthening the casting time by 1 . 0 seconds . Some talents reduce the amount of pushback by 70 % . The reduction is additive to a paladin ' s concentration aura ( another 35 % ) which will negate spell pushback . Note : Before 3 . 0 , spell pushback ranged from 0 . 5 to 1 . 0 seconds per hit and was not limited to just the first two hits , which made casting extremely difficult when repeatedly taking direct damage . Global Cooldown . Haste Formula . The global cooldown for casters with no haste is 1 . 5 seconds . Haste reduces the global cooldown according to the general formula for haste : RatingConversion represents the haste rating required for 1 % haste at a given level . Percentage Reduction . The amount of haste required to reduce the global cooldown to a desired value can be calculated by : Haste Rating . Rearranging the general formula for haste : For example : 500 hasteRating = ( 10 hasteRating * 100 ) * ( ( 1 . 5s / 1s ) - 1 ) To reduce the global cooldown to an arbitrary value of 1 second , it would take 50 % haste or a haste rating of : With raid buffs such as Wrath of Air Totem and Swift Retribution , the number will be lower .