Casting speed calculation

% 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 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.

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.

Losing casting speed

Chance of Ignoring Spell Interruption When Damaged = 100% – Chance to Be Interrupted By Damage

The chance to have your spells delayed by damage is additive. If you have a talent for 70% chance to avoid spell interrupts, and a paladin with concentration aura (another 35%) is in your party, you will not receive any spell interrupts from damage.

NOTE: The Spell Pushback mechanics have been changed as of release 3.0. Now, only the first two damaging attacks received will cause spell pushback, and subsequent damage will not. The talents that used to reduce the odds of spell pushback occuring now instead reduce the amount of casting time lost when pushback occurs.

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:

NewCastTime = BaseCastTime * ( 1 + HasteRating / ( RatingConversion * 100 ) ) ^ 1

RatingConversion represents the haste rating required for 1% haste at a given level.

Haste Rating Required Per 1%
Level 60 Level 70 Level 80
10 15.77 32.79


Percentage Reduction

The amount of haste required to reduce the global cooldown to a desired value can be calculated by:

Haste = ( ( BaseCastTime / DesiredCastTime ) – 1) * 100
For example: 100% haste = ( ( 1.5s / .75s ) – 1) * 100

Haste Rating

Rearranging the general formula for haste:

HasteRating = ( RatingConversion * 100 ) * ( ( BaseCastTime / NewCastTime ) – 1 )

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:

Level 60 Level 70 Level 80
500 788.5 1639.5



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