Penance Priest

Discipline Priest Blog

This tool is years old!! No update is coming though, I'm long out of WoW :)

Here's a little tool, something that I've wanted to do for a while but never quite got around to. It's the javascript equivalent of one of my posts: I start out with the intention to write something nice and simple. Then I get fascinated and pulled in deeper than I planned. Oh well!

It's a calculator for Power Word: Shield. The simplest way to use it is to plug in your spell power and hit calculate. You can also add a “booster,” which is used to mimic the T10 set bonus (5%) and/or the ICC zonewide bonus (5–30%).

(Until I see math indicating otherwise, I'll assume that those bonuses are applied after the normal shield value is calculated. Please link if you've done or seen this math!)

You can also compare two shields. E.g., how much of a boost would your shields get from an additional 100 spell power? The comparison shows both hit points and percentages.

The formula and some useful resources are below.

Spell power:
Boost: %
Spell power:
Boost: %

Here is the formula. For simplicity, I've assumed you're fully talented into all relevant talents.

PWS = (Base+(SP*(coeff+BT)))*(1+TD)*(1+FP)*(1+IPWS)

Base = 2230 for max rank
SP = your spell power
Coeff = 0.8068 (the spell power coefficient)
BT = 0.40 (5/5 Borrowed Time)
TD = 0.05 (5/5 Twin Disciplines)
FP = 0.04 (2/2 Focused Power)
IPWS = 0.15 (3/3 Improved PW:Shield)

Now, whether or not the formula is working as intended is an open question. The comments and bug reports on the WowWiki page are very interesting. That page also lists some tips for using PWS, as well as the history of PWS in patch notes. Highly recommended reading.

Also, Zusterke has a full-featured priest spell calculator. It does much more than this page ever will, including the ability to take less than full ranks of the relevant talents. It also does all priest spells, and works for (gasp!) holy priests too. It's a fantastic resource.

It seems to be a good time for a review of this class-defining talent. I’ve seen many questions about it recently and tons of misunderstandings about how it works. So I started writing a little “hey guys, don’t forget!” piece. It kind of got out of hand. Honest…this really did start out as a simple article, but once I got going, I realized how much there is to talk about! It’s a simple talent, but once you start thinking it through, you’ll see how valuable it is to understand its nuances and implications.

Also, as you’ll see, you can’t really discuss Divine Aegis without including Inspiration and Grace in the mix. They’re all secondary effects of your healing spells.

In fact, I confess. This isn’t an article about Divine Aegis. It’s really about taking your understanding of discipline to a higher level.

There’s a little bit of math in here, but it’s junior high school stuff. No rocket science, I promise.


First, the definition of Divine Aegis:

Critical heals create a protective shield on the target, absorbing 30% of the amount healed. Lasts 12 sec.

Here’s the update to the talent that made us go all a-flutter back in 3.1. It’s an old change at this point, but I still see people forgetting about it:

Divine Aegis effects will now stack, however the amount absorbed cannot exceed 125*level (of the target).

You can stack DA bubbles up to a max of 10k hp on a level 80 friendly. That was big news; before that change, DA was binary (on or off), and confusion was rampant about how it worked in practice. (I.e., what happens when you crit several times in a row?) The 3.1 version of Divine Aegis also takes into account overheal, which makes it just… mwah.

I’ll be using that word (“binary”) quite a lot. It’s just fancytalk for an on/off switch, something with no gray area. Shadowform is binary (you’re in it or you’re not), as is pregnancy, a coin-flip, and whether or not you’re Chuck Norris. There is no gray zone in binaryland.


Here is the definition of a very related talent, Inspiration, which you are not allowed to skip, ever, ever, for any reason, go Inspiration or go home:

Reduces your target's physical damage taken by 10% for 15 sec after getting a critical effect from your Flash Heal, Heal, Greater Heal, Binding Heal, Penance, Prayer of Mending, Prayer of Healing, or Circle of Healing spell.

The same damage-reduction buff is provided by resto shaman in their Ancestral Healing talent.

One more talent, not entirely related, but relevant for our purposes here. The tank-healing disc priest’s wannabe scaling talent, Princess Grace herself:

Your Flash Heal, Greater Heal, and Penance spells have a 100% chance to bless the target with Grace, increasing all healing received from the Priest by 3%. This effect will stack up to 3 times. Effect lasts 15 sec. Grace can only be active on one target at a time.

Only a few spells will proc Grace, but once it’s up, the healing bonus will benefit all of your healing spells. (But no one else benefits; just you.)

I haven’t forgotten that this is supposed to be an article about Divine Aegis. Sort of.

Secondary healing-effect matrix

I wish I had a catchier name for it. Let me know if you come up with one.

Let’s look at which of these secondary effects can be applied when you cast a healing spell. Entries in the table marked “crit%” will only proc when you crit, so not every cast of Flash Heal will proc Inspiration, for example. A “yes” in a column means every cast will proc the effect, not just criticals.

  Divine Aegis



Flash Heal




Greater Heal





crit% (*)

crit% (*)

Yes (*)

Binding Heal

crit% (*)

crit% (*)



crit% (*)

crit% (*)



crit% (*)

crit% (*)



crit% (glyph)







Entries with an asterisk (*) have multiple chances to proc. Other than Penance, these are multi-target heals, so each target will only get at most one application of each effect at a time. Penance, however, can proc multiple times on the same target.

Power Word: Shield cannot proc Divine Aegis, although the heal from the Glyph can. The DA bubble will be 30% of the 20% heal from the glyph. It’s not much, but it’s there. (Also, it's currently bugged so that it only procs DA on shields you cast on yourself.)

Remember the different natures of these three effects. This is important!

  • Inspiration is binary; it’s either up on your target or it ain’t.
  • Grace is a three-step platform. It has zero, one, two, or three stacks on your target, for 3%, 6%, or 9% increased healing.
  • Divine Aegis is a gradual scale from zero to 10k.

You know what? Just because I think it’s really important, I’ll make a graph.

Divine Aegis scales with ____

Quick! Fill in the blank.

If you said “crit,” you’re right!

If you said “spell power,” you’re right!

If you said “haste,” you’re still right, but the relationship is a little more complex. Haste is one of the best stats for a tank-healing disc priest, and certainly speeding up your spell-casts will speed up the application of DA bubbles. But spell power and crit will be easier for us to analyze, frankly, and haste’s effect on DA is more diffuse. We’re not going to get into issues of boss-swing timers, or how fast you can build up DA to its maximum vs. how fast a boss can clobber that bubble. For now, we’ll focus just on maximizing the DA bubble through spell power and crit, and try to assess which stat will have a bigger impact on your DA mitigation.

Average DA per cast

Let’s start with some basic calculations to figure out an average amount of DA mitigation you get for every spell you cast. We’ll use Flash Heal as a reference.

Crit Heal Size = (base heal size) * 1.5
DA Bubble = (crit heal size) * 0.3
Average DA per cast = (DA bubble size) * (your crit rate)


Average DA per cast = (base heal size) * 1.5 * 0.3 * (your crit rate)

The last line is the one that’s the most interesting. Average DA per cast shows the average amount of bubbly protection you get per cast. You won’t get a DA bubble on every cast, of course. This is just an average.

So, how do you raise your average DA per cast? More spell power, and/or more crit. Our next job is to figure out which is better, if your goal is to maximize this mitigation effect.

Spell power vs. crit

If your base Flash Heal hits for 5000, that means you’ll crit-heal for 7500. When you crit, a DA bubble will be created for 30% of that amount, or 2250. And if you have a 40% crit rate, your average DA per cast will be 900. That means: on average, every time you cast Flash Heal, you will see 900 hp of DA mitigation applied to your target. To build up 10k of mitigation (the max we can have at any one time), it will take approximately eleven casts of Flash Heal. Odds are some of that DA bubble will have been chipped away in the time it takes you to cast that many spells.

Now, consider how much your spells benefit from stacking spell power versus stacking crit. Again, I’ll be using Flash Heal as an example. I’m definitely going to ignore the bonus crit from Improved Flash Heal, and I will also ignore bonus healing effects such as Grace and Guardian Spirit.

We’ll take a nicely-geared ICC priest as our baseline, then see what happens when we add a crit gem versus what happens when we add a spell power gem.

The baseline priest will have 3400 spell power and 40% crit rating (raid buffed). Priest “A” will add a single smooth king’s amber; priest “B” will add a single runed cardinal ruby. Let’s peek at what happens, shall we? We turn to Zusterke’s excellent Spell Calculator, which, while it’s a work in progress, is awesome.


With crit gem

With SP gem

Flash Heal




Crit heal amount




Avg FH amount




DA amount




Avg DA per cast




Total Avg Heal + DA




WHOA NUMBAHS!! Let’s go through them slowly.

The first three rows show how much your Flash Heal hits for, not including Divine Aegis. The base heal, the crit heal, and an average that includes your crit rate. So our baseline priest will see an average Flash Heal of 5966, which assumes that 40% of his casts will crit. The average heal amount is in the blue-tinted row.

The next two rows show how much DA mitigation we can expect. The first row, “DA amount,” shows how much of a DA bubble you’ll see when you crit. The next row, tinted orange, shows the average amount of DA per cast, which we discussed above.

If you add the two tinted columns together, you’ll get the total amount Flash Heal will hit for, including DA mitigation. This total is in the dark gray row.

As you can see, using a crit gem will increase the size of your DA bubble more than it will if you use a spell power gem. (This is in the orange row.) However, the spell power gem will increase your average heal amount more than the crit gem will (the blue row).

The net effect? Both crit and spell power will benefit you. Crit has a bigger effect on DA, while spell power has a bigger effect on your base heal. Overall, spell power is more powerful.

Chances to proc

In every discussion I’ve seen about Greater Heal, someone makes the point that two Flash Heals have more chances to proc Divine Aegis than a single Greater Heal. Do you see the flaw in that thinking?

I sure hope so! DA is not binary. It scales. So while GH takes twice as long to cast as FH, it also has twice the average DA per cast. Over the long haul, they will create very similar amounts of DA mitigation. One will create smaller shields more often, the other will create fewer, larger shields.

(That’s a quickie generalization that doesn’t take into account Divine Fury or your use of Borrowed Time to accelerate GH, nor does it take into account the crit bonus from Improved Flash Heal. I’m merely debunking the idea that “chance to proc” is relevant at all when it comes to Divine Aegis.)

The other two secondary effects (Inspiration and Grace) both work on a chance-to-proc basis. Inspiration is binary, and can be applied by any direct heal. Grace is stair-stepped. So if you need to apply Grace quickly, you need to cast more spells (or use Penance for a triple-shot).

Here’s that graph again! So simple, but it shows so much.

Smooth vs. spiky DA

Here again is our formula, which illustrates how DA scales with spell power and crit rating.

Average DA per cast = (base heal size) * 1.5 * 0.3 * (your crit rate)

As a thought experiment, I’m going to go to the lab and create two Frankenpriests. The first one will be monstrously oversized in the spell power department, but barely have any crit rating at all. This means he will almost never crit, but when he does, the DA bubble will be tremendous because of his super-sized spell power. Spiky DA.

Frankenpriest #2 will have insane amounts of crit, but just a tiny bit of spell power. He’ll be critting on every cast, but each DA bubble will be small. Smooth DA.

Over the long term, the DA protection these two deformed priests provide might very well be equal, or close to it. However, Frankenpriest #1 will be creating huge bubbles (rarely), and Frankenpriest #2 will be creating a large number of tiny bubbles.

Which is better? Well, as long as you’re not overshooting the 10k cap (in between boss swings), either should be fine. Just get your DA up as high as you can, as quickly as you can.

But certainly having a higher crit rate is one way to take the RNG out of the equation. If you had 100% crit, you would never wonder if you got a DA bubble. You’d have one every time. So the higher your crit rate, the less of a factor RNG will be for your tank heals. And we all know that bosses don’t kill tanks; RNG kills tanks.

So in a sense, the smoother DA profile (higher crit rating) is better for maximizing your mitigation. Marginally. If you go telling anyone I just advised you to stack crit, I will deny it vehemently.  Because tank healing is not only about Divine Aegis. If at any point your tank’s green bar dips below 100% -- and it certainly will – the priest with more spell power will be helping more. Go back up to the blue row in my chart above. Spell power is still the way.

Short story: Get tons of crit on your gear, and gem for spell power.

In sum

I’m exhausted! We just covered an entire semester of Disc Priest University in under 2500 words. Your summary is this:

  • Divine Aegis is good.
  • It scales with spell power and crit rating.
  • DA scales better with crit than with SP, but overall, you benefit more from SP than from crit.
  • DA protection is not binary; it can scale up to 10k of mitigation at any time.