Math Reference: Haste Calculations

I’m going to try to put together some reference notes for mathy questions I get on twitter.

Percentage based haste buffs multiply together, while rating based buffs are added to your current haste rating & then converted into a single haste percentage, then treated as one of the percentage effects

Formula: (1 + Haste%) * (1 + Haste%) * (1+Haste%) … – 1

Multiplying decimal values under 1 would result in a very small number, which is why we add the haste buffs to 1, and multiply the resulting values. To return to the expected value, we subtract 1 off the end.

eg: (1+0.3) * (1+0.05) * (1+0.25) – 1 = 70.625% haste

This isn’t quite how they are applied, even if the same result is reached. Haste buffs reduce the cast time of a spell by dividing it by 1+Haste%

eg: 2/(1+0.3) = 1.538

To apply multiple haste effects you keep dividing by each additional percentage source

eg: 2/(1+0.3)/(1+0.05)/(1+0.25) = 1.172

We get the same result if we just apply our total percentage from earlier

eg: 2/(1+0.70625) = 1.172

You can even reverse calculate the haste percentage

Base cast/New Cast = 1 + Haste %

2/1.172 = 1.70625

About binkenstein
I'm a geek, living in Christchurch, New Zealand.

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