Damage calculation

Damage in Guild Wars refers specifically to an action taken by an attacker to remove a portion of an enemy's health. It does not mean the casual "damage" as in "hurt the other guy." This definition includes any attack or skill (including spells) but does not include health degeneration.

When an attacker attempts to damage a target, the following is factored in:
 * The damage type. This will determine the enemy's armor and natural resistences to that damage.
 * The attacker's ability to inflict the damage.
 * The target's ability to resist this damage.
 * Bonuses on both side. An attacker may have bonuses that augment the damage and the target may have bonuses that reduce the damage.

Below is a breakdown of these factors:

Damage Types
There are several different types of damage in Guild Wars.
 * Elemental damage
 * Fire damage
 * Cold damage
 * Lightning damage
 * Earth damage
 * Physical damage
 * Blunt damage
 * Piercing damage
 * Slashing damage
 * Armor Ignoring Damage
 * Holy damage*
 * Shadow damage
 * Untyped Damage
 * Other damage:
 * Light damage
 * Dark damage
 * Chaos damage

* Holy damage only selectively ignores armor. See the article for details.

Damage Calculation
''Note: For the purposes of simplicity, the term attack is used loosely below to describe an atempt to damage an opponent. However, whenever the word "attack" is used in skill descriptions, it refers to the attack action.''

Every damaging action has a base damage (BD) indicated in the skill or weapon description. Weapons have a range of possible values from which an attack-specific BD is selected uniformly at random. This base damage is modified by damage bonuses (or penalties) on the attacker, and the armor of the target of the attack.

Effect of Armor
Assuming the attack was not blocked or evaded, we first calculate the effective armor level (EAL) the target has against that attack. Note that this value can vary greatly depending on the attack. At one extreme are attacks that "ignore armor" – they impart the full damage regardless of armor or armor bonuses. Examples include any attack that deals shadow damage, or offensive spells such as Obsidian Flame. Most attacks, however, are resisted by some form of armor.

Every piece of armor worn by a character has a specific base armor level (BAL). The maximum BAL of spellcasters is generally 60 (Droknar's Armor or later), and rangers and warriors have armor with higher BAL. To the base AL we add any AL that is specific to the type of damage. Many warrior armors have armor bonus versus physical damage; all ranger armors have bonuses versus elemental damage; and elementalist armor sets have bonuses versus specific kinds of elemental damage. Weapons and shields can also yield AL bonuses. Enchantments such as Shield of Regeneration or Armor of Earth, and skills such as "Watch Yourself!" add temporary AL bonuses. Finally, hexes such as Weaken Armor and skills such as Healing Signet add temporary AL penalties, which are treated as negative bonuses. We thus obtain the net armor level (NAL).


 * NAL = BAL + AL bonuses - AL penalties

Next, we have to account for any armor penetration present in the attack. Lightning damage and certain kinds of holy damage, for instance, have a set amount of penetration (usually 20%). The warrior attribute Strength increases armor penetration of melee attacks. Weapons can also give armor penetration bonuses. Add up all the various bits of armor penetration to obtain the net armor penetration (NAP). We can now calculate the effective armor level (EAL):


 * EAL = NAL &times; (1 - NAP/100)

The EAL is the amount of resistance that any particular attack receives. Generally speaking, the base damage is scaled exponentially by a multiple of the EAL, but the factors differ for different kinds of damage. We call this damage scaling factor the armor effect (AE).

For damage using melee weapons, bows, and pets, the AE depends on the attrbiute rank (AR) in the corresponding weapon attribute (i.e., Marksmanship, Beastmastery, Hammer Mastery, Axe Mastery, Swordsmanship).


 * AEmelee = 2(5 &times; AR - EAL)/40 

Every 8 ranks in a physical damage attribute thus doubles the net damage. Every rank in these attributes in fact scales the damage by exactly a factor of 2(1/8), or roughly 9%. Note that the effect of cumulative ranks is compounded: 5 ranks don't give a 45% damage increase but (1.095 - 1) &times; 100 &asymp; 53% increase.

For offensive spells and attacks using wands and staves, the AE is scaled differently and corresponds to the level of the attacker (AtL):


 * AEmagic = 2(3 &times; AtL - EAL)/40 

It is important to keep in mind that certain skills such as Greater Conflagration and Judge's Insight change physical damage to nonphysical damage, and therefore change the associated AE. The articles on these skills explain their AE changes in more detail. Only in the early PvE game or in exceptional situations is the EAL actually less than the AR or AtL component of the equation, so the AE generally always reduces the effective damage. The philosophy behind the AE scale can be seen as follows: in the prototypical case where the attacker and target are roughly equal PvP players, the attacker's AR 12 physical attack or AtL 20 nonphysical attack will exactly negate the target's EAL of 60 (minimum for all spellcaster PvP armor).

Note: one can think of armor-ignoring attacks as attacks that simply set AE to 1.

Damage Modifiers
There are two kinds of damage modifiers. The first kind, which we call damage scale modifiers (DScale), reduce the BD by a set factor. We can think of them as a positive real number. The following are some examples.


 * Spells like Life Attunement (DScale = 0.7)
 * Skills like Flurry (DScale = 0.75)
 * Weapons where the attribute requirement is not met (DScale = 0.5)

The second kind of modifier, which we call a damage shift modifier (DShift), alters the final damage dealt to the target. Examples:


 * Enchantments like Strength of Honor on the attacker (DShift = +1..8)
 * Warrior equipment that have innate "damage reduction" on the target (DShift = -0..5)
 * Conditions like Weakness on the attacker (DShift = -66%)
 * Damage bonuses on attacks. For example, Power Shot has DShift = +10..18.
 * Protective enchantments such as Shielding Hands, Reversal of Fortune or Mark of Protection.

Effective Damage
The final effective damage (ED) to a target is related to the above factors in the following way:


 * ED = BD &times; AE &times; DScale + DShift

Now, the entire effective damage might actually be prevented from manifesting on the target in certain situations:


 * Enchantments such as Protective Bond or Protective Spirit cap the total received damage.
 * Damage diversion skills such as Dark Bond or Symbiotic Bond distribute the damage to multiple targets.

Illustrative Examples
[examples and graphs to be added presently]

Damage Groups
It is useful to classify damage into damage groups (especially for PvP).
 * Spike Damage
 * Damage Over Time