Priest Theorycrafting – Haste Rating (Part 4)


  1. Introduction
  2. Mana regeneration
  3. Mana pool
  4. Haste rating
  5. Critical rating
  6. Summary

Calculation of the MP5 value of Haste Rating was a bit trickier and I feel the assumptions made are a little less robust than for mana pool, mana regen, etc.


  • Flash Heal is being spammed (1887 base heal, 80.86% co-efficient and 1.5s cast time)
  • Discipline has 1950 spell power
  • Holy has 2147 spell power
  • 32.8 Haste Rating equals 1% Haste
  • Caster currently has zero haste. The effect of moving from 0% to 1% haste is slightly greater than moving from 6% to 7% haste. However the effect on weighting is very small.
  • 30% over-heal
  • Borrowed Time and Serendipity have been ignored as only FH is being spammed.
  • Latency and Surge of Light procs are ignored.

Firstly we calculate the MP5 value of a Flash Heal. We calculate this so we can figure out how much an additional FH, enabled by haste, is worth.

Flash Heal MP5 value = (base heal + (SP * SP co-efficient)) * SP MP5 value * (1 – overheal %)
Flash Heal MP5 value is 1453.3 for discipline and 1520 for Holy.

Secondly we need to calculate the number of additional casts 1 Haste Rating allows.

Cast time for 1% Haste = Base Casting Time/(1 + (% Spell Haste / 100))
Cast time for 1% Haste = 1.5/(1 + (1 / 100))
Cast time for 1% Haste = 1.48149

Extra casts for 1% Haste = 1.5 – Caste time for 1% Haste
Extra casts for 1% Haste = 1 .5- 1.48149
Extra casts for 1% Haste = 0.014851

Extra casts for 1% Haste (%) = Extra casts for 1% Haste/ Base cast time
Extra casts for 1% Haste (%) = 0.014851 / 1.5
Extra casts for 1% Haste (%) = 0.990099%

Extra casts for 1 Haste Rating = Extra casts for 1% Haste / Haste Rating per Haste
Extra casts for 1 Haste Rating = 0.009901 / 32.8
Extra casts for 1 Haste Rating = 0.030186%

So for each 1 Haste Rating you get 0.030186% additional casts

Finally we bring the parts together to calculate how much MP5 value 1 Haste Rating brings.

Haste Rating MP5 value = FH MP5 value per second * Extra casts for 1 Haste Rating

Haste Rating MP5 value (Disc) = 1453.3 / 1.5 * 0.030186%
Haste Rating MP5 value (Disc) = 0.292463

Haste Rating MP5 value (Holy) = 1520 / 1.5 * 0.030186%

Haste Rating MP5 value (Holy) = 0.305889

I’m pretty sure this section could use some refinement and include perhaps latency at least. I generally play with latency around 300ms. This turns a 1.5s Flash Heal into a 1.8s Flash Heal. A very quick and dirty sensitivity test shows that dropping a 1.8s cast time into the equation results in a Haste Rating MP5 value of 0.243666 for Discipline and 0.254898 for Holy. The reason for this is not that the percentage of additional casts changes (it doesn’t), but that the same healing payload, and therefore equivalent MP5 value, is delivered over a longer timeframe. You get less bang for your buck. Or rather the same bang but for more bucks.

Incidentally the values for spamming Greater heal with 300ms latency are 0.321005 for Discipline and 0.335357 for Holy.

7 Responses to Priest Theorycrafting – Haste Rating (Part 4)

  1. obichad says:

    I’ve been using a haste value of 50% of SP value as it just felt right. Nice to see some calculations backing up those feelings. 🙂

  2. lasitus says:


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  3. jambolo says:

    Your computation is overly complicated (and results in small rounding errors). The value of haste rating is simply the change in healing per second (weighted by the SP MP5 value). Below is a simpler calculation (for holy). It is completely equivalent to yours:

    1 haste rating = ( 1520/(1.5/(1+.01)) – 1520/1.5 ) / 32.8

    The formula can be greatly simplified:

    1 haste rating = 1520/1.5 * 0.01 / 32.8

    I prefer pulling the SP MP5 weight out of the 1520 value for clarity:

    1 haste rating = 2533/1.5 * 0.01 / 32.8 * 0.6 = .309

  4. jambolo says:

    Here is a more troubling issue: increasing haste also increases mana usage. Spamming Flash Heal with 1% haste uses an additional 4.63 mana per second (695/1.5 vs 695/1.485), or 23.2 MP5. Thus, 1 haste rating also results in 23.2/32.8 or -0.706 MP5. Combining the benefit of increased heals and the cost of additional mana results in a negative weight for haste, meaning that increasing haste is a bad idea. The good (?) news is that these values are all inaccurate because they don’t account for crit, procs, talents, and glyphs that increase healing and lower mana cost. I expect the actual value of 1 haste rating to be more than 0, but much less than 0.309.

  5. BobTurkey says:

    @jambolo – thanks for the comments. I realised later that I had gone the long way around to calculate the haste value.

    Your calculation is far simplier than my mess and I might update the post with it at some stage.

    Your second comment is interesting. From a purely mana regen focused point of view you are right, haste is bad. Haste is never going to be a net benefit to your mana regen. The trick is to get a balance between that and throughput.

    Personally i’m not a huge fan of haste as a healer and I think it is more of a personal preference stat than the others.

    Great insight, thx Jambolo.

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