Spell Hit, Spell Penetration, and Resistances

Last updated: 01/07/08, patch 2.3.

When casting a spell at a hostile target, there are effectively three things checked to see if the spell hits and how hard.

  • Can the spell hit?
    This is affected by your spell hit stat and the levels of you and your target
  • How much damage should it hit for?
    This is a calculation of crit chance and damage (if applicable)
  • Is the spell being resisted? (If so, by how much?)
    This is affected by your target’s level, spell resistances, and your spell penetration

 

 

Read on…

The First Calculation: Spell Hit

The Basics

The chance that you have to hit a hostile player or mob with a spell is dependent on the difference in your levels, and how much extra spell hit ability you have (from talents, gear, or your race).

Chance to Hit With Spells, Base Percentages

Target’s Level,
Compared to Yours
PvE PvP
3+ below yours 99% 99%
2 below yours 98% 98%
1 below yours 97% 97%
Same as yours 96% 96%
1 above yours 95% 95%
2 above yours 94% 94%
3 above yours 83% 87%
4 above yours 72% 80%
5 above yours 61% 73%

The above table gives you your base probability of hitting your target, based on level. “PvE” = Mobs. “PvP” = Other players. Bosses (whose level come up as a skull when you target them) are considered to be mobs 3 levels above you.

This is important: You can never have more than a 99% chance to hit with spells! There will always be at least a 1% chance that your spell will miss, no matter how much higher in level you are than your target.

Draenei are a bit special. Draenei priests (and shaman and mages) have a bonus 1% chance to hit with spells, for themselves and their party members.

Draenei Chance to Hit With Spells, Base Percentages

Target’s Level,
Compared to Yours
PvE PvP
3+ below yours 99% 99%
2 below yours 99% 99%
1 below yours 98% 98%
Same as yours 97% 97%
1 above yours 96% 96%
2 above yours 95% 95%
3 above yours 84% 88%
4 above yours 73% 81%
5 above yours 62% 74%

It should be noted that the draenei racial bonus to hit with spells will not allow them to have a better than 99% chance to hit.

Increasing Your Chance to Hit

You can increase your chance to hit through talents, such as the priest class talent in the Shadow Magic talent tree, Shadow Focus. Shadow Focus will increase your chance to hit with shadow spells by 2% (per rank), for a total of 10% if you max it out with 5 talent points.

The talent Focused Power (from the Discipline talent tree) can increase your chance to hit with Mind Blast, Smite, and Mass Dispel by 2% per rank (2 ranks, max of 4%).

Example #1: You are (a non-draenei) fighting a boss. You have only 2 points in the Shadow Focus talent, giving you a bonus 4% chance to hit. A boss is considered to be 3 levels above you, which means that your base chance to hit is 83%. Your bonus 4% from talents will increase your chance to hit with your shadow spells on the boss to 87%.

Example #2: Let’s say you have 5 talent points in Shadow Focus. This gives you a bonus 10% chance to hit with your shadow spells. You are trying to kill a target the same level as yourself. Your base chance to hit is 96% (or 97% if you are a draenei priest). However, you cannot just add in your bonus points from your Shadow Focus talent in this case. You cannot have more than a 99% chance to hit! It “caps out” at 99%. So, your chance to hit with shadow spells in this case is 99%.

Hit Rating

You can further increase your chance to hit will spells through gear. The “Spell Hit Rating” can be tricky to understand, as it isn’t written in clear percentages (just like spell crit).

At level 70, 12.6 spell hit rating = +1% chance to hit.

See the below table for level 70 conversions of spell hit rating to percentages.

Level 70, Spell Hit Rating Converted to Percentages

Spell Hit Rating Percent Increase
13 +1%
26 +2%
38 +3%
51 +4%
63 +5%
76 +6%
89 +7%
101 +8%
114 +9%
126 +10%
139 +11%
152 +12%
164 +13%
177 +14%
189 +15%
202 +16%

Being Hit Capped

You cannot have more than a 99% chance to hit a mob/player. If you can reach the 99% mark, that is called being “hit capped,” as no more gain in the spell hit stat will benefit you. Typically when saying you are hit capped, it means for all enemies that you would typically encounter.

So, for instances/raiding, it means that you have a 99% chance to hit mobs 3 levels higher than you are, which is a +16% chance to hit from gear and talents (and the draenei racial ability, if applicable).

DPS: In PvE (instances, raiding), the highest level mob you will have to face is level 3 levels higher than you (namely: bosses). You need a 16% bonus to your hit in order to have a 99% chance to hit a boss (or, more specifically, be hit capped for boss fights). Draenei priests would only need 15%. If you are a shadow priest with 5 points in Shadow Focus, then that is 10% less that you would need, which means you need 6% (76 hit rating) to be hit capped (or 5%, a 63 rating, for draenei).

Crowd Control: For Shackling and Mind Control in instances, likely the highest level mob you will have to keep controlled as a level 70 player will be level 72. Shackle Undead is a holy school spell that doesn’t gain the benefit of any of the priest hit talents. You need 5% spell hit (4% for draenei) in order to minimize the chances of your Shackle Undead spell from being resisted or breaking early. This would mean a 63 spell hit rating (51 for draenei).

PvP: The most you need to increase your hit by when you are fighting equal level players is 4% (or 3% for a draenei). For shadow priests, that means two points in Shadow Focus is all you would ever need.

Crowd Control Spells and Pulse Resists

It should be noted that crowd control spells will continue to make “checks” to see if the spell holds after it is cast. These are periodic “pulse resist” checks done in small intervals after the spell is successfully cast. So, when casting Mind Control and Shackle Undead, the initial check is made to be sure that the spell takes. After it does, periodic checks are continued to be made to ensure that it doesn’t break early. The chance that the spell breaks early on a pulse resist is the same for each pulse resist check (meaning, the chance that it breaks early on pulse resist #1 is the same chance that it breaks early on pulse resist #8, so reshackling every 15 seconds is as beneficial as reshackling every 40 seconds).

With Mind Control in particular, the chance that the spell breaks early increases when you move the controlled mob/player more than 20 yards away from yourself. This increased chance has nothing to do with pulse resists or spell hit, but is worth mentioning as it is a source of common misconception.

Why do we care about spell hit?

1) There are times when we have to carefully keep a mob crowd controlled, and will want to minimize the chaos that can be caused if the crowd control spell breaks early or is resisted initially.

2) At level 70, spell hit is the best way to increase the DPS of a shadow priest for raiding/instancing (until hit capped). The higher a shadow priest’s DPS, the more mana (and health) s/he can regen for the whole party. Also, with cooldowns on many of a shadow priest’s spells, a resisted spell can be quite annoying.

The Second Calculation: Damage

This is simply how much damage the spell would do, before resistances are taken into account, and also a check on if the spell crits or not. This is a computation of potential damage, nothing more.

The Third Calculation: Resistances

The Basics

The third thing that is checked when casting a spell at a hostile target is how much, if any, of the damage will be resisted. When we take resistances into consideration, a damage spell can do more than just hit or miss. It’s damage can be reduced by: 25%, 50%, or 75% as well. This shows up in the combat log as “Your <spell> hits <target> for <X> (<Y> resisted)”.

Your spell school resistances increases the chance that you will resist spells of a given spell school. When attacking other players or monsters, their spell resistances increase the chance that they will resist your spells.

You can see what your base spell school resistance is by pressing “c” and looking at your character pane. You will have values listed for Shadow Resistance, Nature Resistance, Arcane Resistance, Frost Resistance, and Fire Resistance. There is not a Holy Resistance stat for player characters.

Note: Resistances affect spell schools and not spell lines. (Click here for more information on the difference between spell schools and spell lines.)

The listed resistance stats on your character pane are a total of your:

  • Gear bonuses to resistances (including enchants and gems)
  • Class buffs that affect resistances
  • Potions/elixirs, etc.
  • And your racial bonus (if applicable)

Note that class buffs/auras/totems that increase a player’s resistances do not stack. Prayer of Shadow Protection will not stack with the paladin’s Aura of Shadow Resistance. A shaman’s Nature Resistance totem will not stack with Aspect of the Wild. You will only have the highest amount provided, so keep that in mind.

What Spell Resistance Does

Spell resistance gives a chance to resist spells of the corresponding spell school (shadow resistance for shadow school spells, etc.). How much gets resisted depends not only how much spell resistance you have, but the target’s level as well. Spell resistance can be a number anywhere ranging from 0 to 365 (it can be more than that, but 365 is the practical limit, explanation below). How the numerical stat works out is that it gives you percent chance to resist spells (and damage) of a given school.

There is a formula for this, as follows:

Average Resist Rate of Defender (as a decimal) =
0.75 * (defenderSpellResistance) / (5*attackerLevel)

It should be noted that a defender (whether mob or player) can never have a better than 75% resistance rate from spell resistance. It caps out at 75%. Since the highest level target we can encounter is effectively level 73, the practical upper limit on spell resistance is 365 (or, in terms of PvP, the practical limit is 350 since the highest level we would see is level 70). The 75% maximum in terms of spell resistance can be thought of as just being 5 times the attacker’s level (300 for a level 60 character, for instance).

Example: I am attacking another level 70 player who has a shadow protection buff for 70 shadow resistance. I am hurling every shadow spell I have at the other player. Using the formula above, I can calculate this other player should, on average, resist 15% of the my shadow spells and shadow damage.

0.75 * (defenderSpellResistance) / (5*attackerLevel) =
0.75 * (70) / 5*70 = 52.5 / 350 = 0.15 = 15%

The phrases “resistance rate” and “average resistance” (used interchangeably) may need a little elaboration: It means that spells (and spell damage) from that particular school are resisted at an average rate over time. It doesn’t mean that you will automatically only do (or take) that much less damage.

So, for instance, if a target you are attacking has enough spell resistance to have an average resistance rate of 25% against your spells (computed using the above formula), it doesn’t mean that all your damage spells will individually do 25% less damage. If you average them, then yes, you should see results like that. But some will fully hit, some will be fully resisted, some will do half damage, etc.

Binary and Non-Binary Spells

Spell Resistance functions slightly differently depending on what kind of spell you are casting. There are only two different kinds of spells in this regard: Binary and Non-Binary.

Binary spells as named as such as there are only two outcomes for them; they can either hit or miss. Spells that do no damage, or that have a snare effect built in to them (like Mind Flay or Frostbolt), are binary spells. Examples of some priest spells that are binary: Vampiric Embrace, Mind Flay, Dispel Magic, Chastise.

Everything else is non-binary. Since there is a damage component in them, the damage can be fully resisted, 75% resisted, 50% resisted, 25% resisted, or can hit for normal damage. Some priest spells that are non-binary: Mind Blast, Holy Fire, Shadowguard, Smite.

DoTs like Vampiric Touch and Shadow Word: Pain are binary in their initial cast, but each damage tick can fall victim to resists just as a non-binary spell.

Effective Resistance

There are other things that can affect spell school resistance that would not show up on a character pane. The chance that a spell is resisted depends on the amount of effective spell school resistance a mob or player has to the school of magic that you are casting after all these other factors are taken into account.

The initial effective spell school resistance is just the school resistance stat (mentioned above) corresponding to what is being cast (the target’s shadow resistance for when you are casting shadow school spells, etc.). Most mobs will have no base resistances, and most players will only have what is granted to them by racial bonuses (dwarves’ frost resistance, etc.) or from class spells (Shadow Protection, etc.). This is also modified by gear, enchants, etc., as mentioned above.

The second thing that could change a target’s effective spell resistance is the difference in level between you and your opponent. For non-binary spells only: Each difference in level gives a 2% resistance chance that cannot be negated (by spell penetration or otherwise). In other words, if you are attacking a mob three levels higher than yourself (like a boss), even if that mob has no base spell resistance to speak of, the level difference between you an it awards it a non-negatable 6% spell resist against the spell school you are casting from (a total of 24 spell resistance if you are level 60, 28 at level 70). Again, let me repeat, level-based spell resistance applies to non-binary spells only.

Here is a table illustrating how much level-based spell resistance your target would have per level, depending on your level:

Your Level Target’s Bonus SR (per level)
10 1.33
20 2.67
30 4
40 5.33
50 6.67
60 8
70 9.33

A basic formula to determine the amount of level-based spell resistance granted would be: levelDifference * bonusSRperLevel.

Example: You are level 60 attacking a target four levels higher than you. That target will then have an non-negatable 32 spell resistance against your non-binary spells.

The last thing that modifies the effective spell resistance is the amount of spell penetration the attacker has. Each point of spell penetration reduces the base spell resistance of the target by a point (but it cannot be reduced below zero, and it cannot off-set the level-based spell resistance for non-binary spells as mentioned above).

Calculating Effective Spell Resistance

The target’s effective spell resistance is equal to its base spell resistance (from racial abilities, gear, buffs, items, etc.) minus your spell penetration. For non-binary spells, it is then increased by a 2% rate in resistance per each level higher the target it than the caster.

As a formula for a target’s effective spell resistance against you:

spellpen.gif
Notes: Total cannot go below zero. Level-based spell resistance only affects non-binary spells.

Example: You have 10 spell penetration. The player you are attacking has a Shadow Protection buff for 70 shadow resistance. This player now only effectively has 60 shadow resistance against you, not 70.

Example: You are attacking mobs two levels higher than you are that have no special spell resistances to speak of. Given your level, and the level difference between you and the mobs you are fighting, they effectively have 10 spell resistance against you. Even if you have 10 spell penetration (or more), these mobs will have 10 spell resistance from being higher level. Your spell penetration cannot change this.

An important note: Blizzard has (supposedly) removed all instances and mechanics of negative spell resistances from the game. Spell penetration and level differences will never lower a player’s or mob’s spell resistance below zero; zero is the lowest effective spell resistance can be.

Resistances, and Binary Spell Hit Chance

Spell school resistances can cause a binary spell to sometimes miss. This can be calculated as a simple expression.

Your effective spell hit is:

Spell hit chance * Resistance non-mitigation chance
Or, simply: H * R

Your spell hit chance was what we discussed in section “Calculation 1: Spell Hit” above. Your “resistance non-mitigation chance” sounds complicated, but is isn’t.

We used this formula from above to calculate Average Resist Rate:

0.75 * (defenderSpellResistance) / (5*attackerLevel)

As that expression provides the average rate that spells go mitigated, for the non-mitigation chance, we just need to subtract that value from 1.

1 – 0.75 * (defenderSpellResistance) / (5*attackerLevel)

And that is your resistance non-mitigation chance.

Example: I have a 96% chance to hit (with talents, gear, etc.). The target I am attacking has a 20% chance to resist spells of that school. A 20% chance of resist, means that there is an 80% (or, 100%-20%) chance that the spell will go unmitigated. So: .96 * .8 = .768 = ~77% chance that the spell will hit.

Reminder: Since we are talking about binary spells here, the level-based spell resistance does not come into play as a part of the “defenderSpellResistance” used. That is just the base spell resist minus any spell penetration the attacker may have.

Resistances, and Non-Binary Spell Hit Chance

For non-binary spells, it is best to think of it as a two-step system. You have to pass the first barrier (spell hit), then you get a chance at the second (spell resistance). Spell resistance can cause a non-binary spell to be fully resisted, and it will show up as a miss in your combat log. There is no way to differentiate a complete resist (due to spell resistance) from a miss (due to spell hit).

Blizzard has a delightfully vague page on the Warcraft official site that illustrates that your spell hit on non-binary spells can greatly varies depending on the resistances of your target. As the function to determine effective spell hit with resistances taken into account on non-binary spells cannot be modeled in any linear fashion, it really is best thought of as two separate calculations, for simplicity’s sake.

The following table was extrapolated from the Blizzard page:

resistc.gif

It shows, based on mitigation percent, the chances of a spell being: fully resisted, 75% resisted, 50% resisted, 25% resisted, or not resisted at all.

In a general sense, looking at the above table, you can see that as mitigation percent gets smaller, the chance that the non-binary spell gets fully resisted hit zero. Thus, we can say that for non-binary spells, your spell hit chance is essentially just your base spell hit chance, provided the spell resistance of your target is adequately small.

Why Do Spell Resistances and Spell Penetration Matter?

In PvE:

  • It is important to understand that if you see a lot of partial resists on your spells that the mob you are attacking either higher in level than you are, or has a base spell resistance. If it is level-based, then it can not be overcome.  If it from base spell resistances that the mob may have, then overcoming that requires spell penetration, and not spell hit.
  • As it is very rare that you will come across mobs with dangerous amounts of spell resistance, using the spell penetration in PvE encounters is typically wasteful. Level-based spell resistance, which is what is encountered most commonly, cannot be negated by spell penetration.
  • Shadowpriests: If you encounter mobs in raids that have a decent amount of shadow resistance (beyond the level-based spell resistance), a Curse of Shadow from a warlock will typically negate the shadow resistance for you.
  • There are times in certain PvE encounters when you may need to equip yourself with spell resistance gear to survive attacks or environmental damage from mobs. (More info here.)

In PvP:

  • Players will typically have buffs that grant them spell resistance (like Prayer of Shadow Protection, Mark of the Wild, etc.). At level 70, it would take about 40 to negate Mark of the Wild, and 70 to negate Shadow Protection. Spell penetration, while a cheap stat to itemize with, is not worth the sacrifice of “defense” stats (resiliance, stamina), unless you have an adequate amount of them. You can get your (level 35+) cloak enchanted with +20 spell penetration (a prime choice for most offensive casters).
  • There is no holy spell school resistance in the game for player characters, so if you rely on holy DPS in PvP, it is not worth it for you to use spell penetration.

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One Response

  1. […] being resisted or breaking early. This would mean a 63 spell hit rating (51 for draenei). (Source: Spell Hit, Spell Penetration, and Resistances A Dwarf Priest) In short: you need hit gear, not the hit talent which does not benefit the holy school in which […]

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