Related Questions:
How does 50% extra xp weekend stack with other bonuses?
Extra experience from equipment
While there is some good information in the answers to the above questions, I feel none of them give the complete picture.
In Diablo 3, there are a number of different ways to increase your exp gain. Assuming your level is fixed (at 70, most likely), we have the following effects:
- "Strength in Numbers" buff (group bonus)
- "Increases bonus experience by ..%" from equipment and/or ruby in head slot
- "Monster kills grant +... experience" from equipment and/or Gem of Ease
- Difficulty bonus (a % bonus)
These all modify the base experience received from slaying a monster (again, assuming for simplicity that player level isn't taken into account). For simplicity, I will refer to them as (in the same order).
- Group%
- Bonus%
- Bonus
- Difficulty%
Now, how these work on their own is pretty straightforward, but how do they stack when two or more are present? Knowing the exact way they stack could make a big difference when evaluating different item properties.
For example, having "Monster kills grant +... experience" on a few pieces of gear could make a big difference if the calculation is something like:
Net gain = (Base + Bonus) * Group% * Bonus% * Difficulty%
However, it would be almost useless at higher difficulties if the formula was more like:
Net gain = Base * Group% * Bonus% * Difficulty% + Bonus
The names aren't very descriptive, but if I had to guess, my guess would be something like:
Net gain = (Base + Bonus) * (Bonus% + Difficulty%) * Group%
However, this is mostly guesswork. Is there any official source (or someone doing a bunch of science) that clears this up? I also remember someone saying there was a difference in how experience gain was calculated in Greater Rifts compared to the rest of the game. Any truth to this?
(Note: When multiplying by X%, I naturally mean multiplication by 1.00 + 0.01*X. Multiplying by (X% + Y%) refers to a multiplication by 1.00 + 0.01*(X + Y))
Edit: While broad in scope, the question primarily applies to the current (as of August 2015) state of the game. So patch 2.2.1 primarily (which also applies to season 4/patch 2.3.0, since there are no changes to the exp formula planned, only base exp balancing and bonus exp being averaged over the party).