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.''

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. Finally, enchantments such as Weaken Armor and skills such as Healing Signet add 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.

Now we turn to damage: every attack has a specific base damage (BD) value indicated in the skill or weapon description. (Weapons actually don't have a single BD value, but a range of possible values; at the time of attack, an attack-specific value is selected uniformly at random from this range.) We are now ready to calculate the net damage (ND). Generally speaking, the net damage is the base damage scaled exponentially by the EAL, but we can be more precise.

Net Damage Due to Melee Weapons and Bows
The attributes Marksmanship, Hammer Mastery, Axe Mastery and Swordsmanship scale the base damage exponentially by a multiple of the attribute rank (AR) corresponding to the attacker's melee or ranged weapon. Precisely, the equation is:


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

Every 8 ranks in an attribute doubles the net damage. In fact, every rank in a weapon attack attribute scales the damage by exactly a factor of 2(1/8), or an increase of 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.

As the equation makes clear, an AR of 12 against an EAL of 60 completely negates the scaling factor, making ND equal to the BD. This is the reason why you may often hear that an AR of 12 is "needed to counter armor".

Net Damage Due to Spells
Warning: This subsection of the article should be taken as mostly speculative.

Unlike melee attacks, spells always see the full 60 in the exponent of the ND equation. However, spell damages are sensitive to the character levels of the attacker and target. There is a damage bonus if the attacker is of a higher level than the target (or a damage reduction if the reverse). Precisely, for every 13 levels of difference the net damage output is doubled (or halved), giving the equation:


 * NDspells = BD &times; 2(60 - EAL)/40 + (AtL - TgL)/13 

(where AtL and TgL are the attacker and target levels respectively).

For the case of PvP the level difference is completely irrelevant. However, this difference is important for high level spellcasters in difficult PvE areas such as Sorrow's Furnace or the Realms of the Gods. Level 30 spellcasting mobs are rightly feared, as they are exponentially stronger than level 20 spellcasters in your team.

Effective Damage
The above equations for net damage hint at a basic rule of thumb for damage: assuming roughly equal opponents, if the EAL is more than 60, then the net damage will be less than the BD; dually, an EAL of less than 60 gives an actual damage of more than the BD.

Net damage is not always the effective damage dealt to the target. Certain weapons or enchantments like Judge's Insight offer a damage bonus that is added to the ND. Effective damage can also be reduced. The condition Weakness, for example, reduces net damage by melee by 66%. Certain shields and warrior armors have an innate "damage reduction", which is simply subtracted from the ND. With these final modifications taken into account, we get the effective damage (ED) dealt to the target.


 * ED = ND + damage bonuses - damage reduction

Of course, enchantments like Protective Spirit or Protective Bond might prevent the entire effective damage from actually manifesting on the target.

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