A stacking penalty is a penalty to the effect a module has on your dropsuit or vehicle fitting. The penalty takes effect when you mount more than one module that affects the same attribute of your fit.
Not all modules have stacking penalties, so check the description tab in the module's info window to be sure. Modules with stacking penalty will have this phrase: "NOTE: Stacking penalties apply to this module: the effectiveness of each additional module (after the first) that alters the same attribute will be reduced." This means that adding another module (after the first), that that affect the same attribute, will result in a lesser bonus than the first. This mechanic is in place to prevent dropsuits and vehicles from obtaining very high effects by simply using many of the same module.
For example, if a player were to add a module that boosted their weapon damage by 10%, then a second identical module, the second module would only add about 8.7% instead of the full 10%. The total increase would be 18.7% more damage instead of the expected 20%.
As a rule of thumb, adding more than four modules of a single type with a stacking penalty results in insignificant gains.
Stacking penalties implement diminishing marginal returns (see ) for bonuses. Every additional bonus added to an attribute has its effect diminished until there is practically no incentive to add another bonus.
The formula for the stacking penalty is:
S(n) = 0.5^[((n-1) / 2.22292081)^2]
n = the nth module added
S = stacking effect for this particular module addition
From this, we can know the following:
|Modules||Effect of nth module||Cumulative bonuses with N modules, each giving 10%||Cumulative bonuses with N modules, each giving 20%|
|1||100%||10 %||20 %|
Adding more than 3 modules of same type brings only very minor bonuses - fourth module will bring only 2.83% instead of 10% bonus (or 5.66% instead of 20%).
Modules with stacking penaltiesEdit
Infantry & vehicle modules: Edit
- In EVE Online, there was originally no stacking penalty; this caused all manners of havoc with players equipping many modules of the same type. Ships with many low slots would wield many damage enhancing modules for firepower that could instantly vaporize almost anything.
- The Red Moon Rising EVE Online expansion tweaked the stacking penalty. Originally, it only diminished the second module, and didn't have much effect thereafter.