Five second rule

The five second rule was a mechanic which affected mana regeneration prior to patch 4.0.1. It prevented a character's mana from regenerating 5 seconds after casting a spell. This was an important concern for mana-using classes, especially healers. Prior to patch 1.4.0, mana regeneration also stopped while casting a spell; hence many in-game references to the five second rule would be use the phrase "during casting" instead of "after casting."

Because the activation of the five second rule was dependent on mana expenditure, mana regeneration would continue if a character cast a "free" spell by the means of clearcasting. The same applied to any spell (i.e. Nature's Swiftness) which cost 0 mana. This could be useful when trying to regenerate mana, but still being able cast one free spell without interrupting mana regeneration (for instance in case of an emergency.)

The old "Mana per 5 seconds" (MP5) stat was not affected by this mechanic, and always provided the stated amount of mana regeneration.