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'''Lifesteal''' is a mechanic which heals a player by a portion of the damage they deal to an opponent. There are two main types of lifesteal, each with an associated [[stats|stat]]: {{plink|Bullet Lifesteal|pic=AttributeIconBulletLifesteal}}, which returns a portion of the [[Bullet Damage|bullet damage]] dealt, and {{plink|Spirit Lifesteal|pic=AttributeIconSpiritLifesteal}}, which returns a portion of the [[Spirit Damage|spirit damage]] dealt. Bullet and Spirit Lifesteal are calculated identically, but are affected by different [[item|items]].

== Formula ==

Despite being presented in-game as +X% Bullet/Spirit Lifesteal, different sources of lifesteal stack multiplicatively, not additively. With <math>n</math> different sources of the same category of lifesteal, final lifesteal <math>L_F</math> is given by:

<math>L_F = 1 - \prod_{i=1}^n (1 - L_i)</math><br/><!--this is rounded, but the game displays two different calculations where one is rounded up, and the other is rounded down-->

where <math>L_i</math> is the lifesteal provided by the <math>i</math>th source. Bullet and Spirit Lifesteal are calculated independently of each other, but both use the same formula.

Lifesteal against creeps (non-hero units) is reduced compared to heroes:

* Bullet Lifesteal vs. creeps: 60% of the calculated value

* Spirit Lifesteal vs. creeps: 40% of the calculated value

With 22% Bullet Lifesteal from {{item|Fury Trance}} and 30% Bullet Lifesteal from {{item|Leech}}, the player's final bullet lifesteal is:

<math>L_F = 1 - (1 - 0.22) \times (1 - 0.30) = 45.4%</math><!--the stat ingame says 45%-->

This means that any time the player deals bullet damage to any opponent, they will immediately be healed by 45.4% of the damage dealt. Note that the in-game user interface is inconsistent in how it rounds the final lifesteal percentage.

The debuff applied to opponents by {{item|Spirit Shredder Bullets}} behaves differently from all other lifesteal items. It does not affect the user's Spirit Lifesteal stat, nor is it factored into the formula above; instead, it ''adds'' a flat +8% spirit lifesteal against an affected target while the debuff is active. For example, if a player has Spirit Shredder Bullets, {{item|Spirit Lifesteal}} (+16%), and {{item|Leech}} (+30%), their spirit lifesteal against a target affected by Soul Shredder Bullets would be:

<math>L_F = [1 - (1 - 0.16) \times (1 - 0.30)] + 0.08 = 49.2%</math>

Their spirit lifesteal against a target not affected by Soul Shredder Bullets would instead be 41.2% (equal to their Spirit Lifesteal stat).

Melee Lifesteal is not a stat. The item {{item|Melee Lifesteal}} and its upgrade {{item|Lifestrike}} both provide a passive ability which heals the user by a percentage of their [[Melee Damage|melee damage]] dealt, but they behave differently from Bullet and Spirit Lifesteal. These abilities activate for one melee attack, then go on cooldown for several seconds, during which no further health can be regained from melee attacks; Bullet and Spirit Lifesteal are always active and have no associated cooldowns. These items also grant a flat healing bonus on activation, and are less effective against non-[[hero|heroes]], neither of which is true of Bullet and Spirit Lifesteal.