Threat

Threat is a measure of an NPC's aggression towards a player. Each NPC has a threat table, and the character at the top of the list is usually the target of its aggression. In-game, this is known as having aggro from that particular NPC. The NPC will attack that character if possible, unless another character manages to change the NPC's target.

Negative threat
Threat does not determine whether or not a mob will attack, only what it will attack if it does. A player's threat value cannot drop below 0, and reaching 0 threat does not remove a player from combat with the mob.

Changes to threat levels
Several abilities and effects increase a character's threat level against a mob. Note that the effective amount of threat generated can be modified by talents and spells. See the Threat Tables below for details.

Basic NPC attacks on a player do not modify threat; a character being attacked is neither gaining nor losing threat from it. However, some NPCs have special moves that affect threat.

Damage is the most basic form of threat generation. Threat measurements are normalized so that 1 point of damage generates 1 point of threat (the in-game threat meter treats 1 damage as 100 threat, as explain below).

Many abilities generate additional threat that is not tied to their effect (damage dealt, buffs, debuffs). The bonus threat values are listed below.

Threat caused by beneficial effects is divided amongst all NPCs that are aware of the character. This global threat applies to heals, bonus threat from buffs (such as Battle Shout or Arcane Brilliance), and power gains (such as a Mana Potion or Rage Potion).

Healing threat is global, and is normally .5x of the amount healed. Healing effects cause no threat if the target is already at full health.

Example: Player 1 is involved in combat with 5 mobs. Player 2 (priest) heals Player 1 for 1000 health, and has no threat reduction talents. A 1000 heal generates 500 threat, however that 500 threat is split amongst the 5 mobs. Each of the 5 mobs now has 100 threat towards Player 2.

If a power gain (Rage/Mana increase) shows up in the combat log, the effect usually counts as a buff with bonus threat attached to the event. There are no Energy-increasing effects that appear to cause bonus threat. Normal power regen does not generate threat. Normal health regen also does not generate threat.

For debuffs and attacks, any bonus threat is divided amongst the affected targets. For example, the bonus threat of Cleave is divided between the 2 targets of the attack, while the bonus threat of Sunder Armor is applied directly to the target of the attack. Many abilities, particularly tanking abilities such as Shield Slam and Rune Strike, have a threat multiplier instead of or in addition to a bonus threat value.

Tank threat bonus
Classes that are designed to fulfill a tanking role now gain additional threat when they are in that mode. This mode is triggered by Death Knights with Blood Presence active, Druids in Bear Form, Paladins with Righteous Fury active, and Warriors in Defensive Stance. Bear form doesn't specify that it increases threat, but the threat increase is still active.

While in tanking mode, the character's threat is further multiplied by 3.0x. This was done in order to simplify threat modifying buffs, and allowed for the removal/change of Blessing of Salvation and Tranquil Air Totem.

In-game threat values
With the release of v3.0, WoW now provides the players with threat values on your target. These values are normalized differently: they are 100x damage done instead of 1-to-1. This is most likely done to optimize for integer calculations, rather than slower floating-point math. For the purposes of this article, all the values shown still use the 1:1 normalization for simplicity.

Threat tables per class
Threat auras affect the threat value of all abilities under their jurisdiction of effect that are used while the threat-modifying aura is active (which is always, in the case of passive modifications). Threat-modifying abilities have a direct effect on the threat level of one or more characters. Note that static values added to the threat an ability generates are added before threat auras are applied, and thus are increased or decreased by any threat auras that may be active when the ability is used. The static values listed in the chart below are the base values before threat auras.

An increase in threat by X% is equal to multiplying the current modifier (which begins at 1.0) by (1 + X%/100); for example, a threat increase of 20% would be a multiplier of 1.20. Likewise, a decrease in threat by X% is a multiplier of (1 - X%/100); a threat decrease of 30% would be a multiplier of 0.70.

Threat modifiers stack multiplicatively when calculating the threat for an ability affected by more than one modifier. The final threat modifier for an ability is determined by multiplying all the active modifiers together; if the previous two examples were active simultaneously, the total threat caused would be 1.00 (baseline) * 1.20 * 0.70 = 0.84, or 84% of the threat that you would have caused without multipliers.

NOTE: The threat system was heavily overhauled again for Cataclysm and Patch 4.0.3. The numbers in these tables have been updated to the extent of understanding that community research has achieved so far; any pre-Cata values that have not been verified or updated for the post-4.0 game are currently italicized to indicate that their values may be incorrect or outdated. Also, be aware that many ability pages have not been properly updated for the post-Cata values and may contradict the values in this table.

Finally, note that the in-game threat meter (introduced in Wrath) does not use the decimal notation the table does; instead, the baseline modifier is considered to be 100. For example, causing 100 damage would cause (100 * 1.0) = 100 threat by this page's system. The in-game threat meter, however, would consider 100 damage as causing (100 * 100) = 10000 threat. Likewise, the 300% threat modifier of Defensive Stance would be 3.0x for all threat caused, while the in-game threat meter would consider all threat to be multiplied by 300 while in Defensive Stance.

Stacked threat auras
Threat auras stack in a multiplicative fashion. A common but wrong assumption is that due to this mechanic, threat reduction effects provide less benefit the more a player has; in fact, threat reduction is always equally powerful, no matter how much a player has.

Example: You are a Priest casting a Binding Heal. Threat is normally 0.5x healing done, and Binding Heal has an additional 0.5 modifier built in:

Your healing threat would be: 0.5 * 0.5 = 0.25x healing done.

Videos
EOIMvEVCtxU

Additional notes

 * Being noticed by an aggressive NPC does not generate any threat. This behavior places that character on the NPC's threat list, but with a threat value of 0.
 * Threat doesn't decay (passively degenerate over time) unless a specific encounter is designed that way. The exception to this rule is threat generation by abilities such as Misdirection or Tricks of the Trade.  Threat generated from these abilities disappears after 30 seconds.
 * A character's threat level is reset if the character leaves combat with the mob (dies, moves far enough away).
 * A character's threat level cannot be negative.