Stacking penalties

Stacking penalties refer to an effectiveness reduction that is incurred when using two or more modules or rigs that affect the same attribute. The more modules or rigs affect the same attribute, the less effective each additional module is; in practice, having more than three or four modules/rigs affecting the same attribute is not worth it.

Normally, the benefits of additional modules/rigs would be multiplicative. So if fitting one Speed Booster (a fictional module with nice round numbers to make the math easier to understand) module increases a ship's speed by 10%, fitting two of them would increase a ship's speed by 21% ((1 + 10%) × (1 + 10%) = 1.1 × 1.1 = 1.21), and fitting three would increase it by 33% (1.1 × 1.1 × 1.1 = 1.33).

However, due to the stacking penalties effect, the second, third, and fourth Speed Booster modules' effects are only partially effective (86.9%, 57.1%, and 28.3% respectively - see below for details), and would therefore only increase a ship's speed by:

• 10% × 86.9% = 9% for the second module
• 10% × 57.1% = 5.7% for the third module
• 10% × 28.3% = 2.8% for the third module

Therefore, the actual speed increase for the ship would be:

• One Speed Booster module: +10%
• Two Speed Booster modules: (1 + 10%) × (1 + (10% × 86.9%)) = (1 + 10.5%) × (1 + 9%) = +19.8%
• Three Speed Booster modules: (1 + 19.8%) × (1 + 5.7%) = +26.7%
• Four Speed Booster modules: (1 + 26.7%) × (1 + 2.8%) = +30.3%

However, the modules' bonuses still multiply, so even if the percentage increase of each subsequent module decreases sharply, the absolute increase of each subsequent module drops off more slowly. If we take a ship with a nominal speed of 100 m/s:

• Adding one Speed Booster module: 100 + 10% = 110 m/s, an increase of +10 m/s
• Adding a second Speed Booster module: 110 m/s + 9% = 120 m/s, an additional increase of +10 m/s
• Adding a third Speed Booster module: 120 m/s + 5.7% = 127 m/s, an additional increase of +7 m/s
• Adding a fourth Speed Booster module: 127 m/s + 2.8% = 130 m/s, an additional increase of +3 m/s

Most (but not all) modules and rigs have show in their description if they are subject to stacking penalties.

Note that it is the stat bonus that is affected, not the module itself. For example, if you fit both a Nanofiber Internal Structure (boosts agility and velocity) and an Overdrive Injector System (boosts velocity), the Nanofiber's velocity bonus would suffer a stacking penalty, but not its agility bonus. Similarly with armour or shield resistance modules: if you fit an EM hardener, an explosive hardener and an omni-hardener (Adaptive Invulnerability Field or Adaptive Nano Plating): the EM/Explosive resistances from the omni-hardener would be stacking-penalized but the Kinetic/Thermal resistances would not.

Also of note is that module drawbacks (negative effects) can also be stacking penalized.

The Formula

Stacking-penalized modifiers are applied one at a time, in descending order of strength.

The n-th modifier is multiplied by S(n-1), as follows:

S(u) = e^{-(u / 2.67)2}

The Numbers

• 1st mod: 100.0% effectiveness
• 2nd mod: 86.9% effectiveness
• 3rd mod: 57.1% effectiveness
• 4th mod: 28.3% effectiveness
• 5th mod: 10.6% effectiveness
• 6th mod: 3.0% effectiveness

As is clear, stacking more than 3 or 4 modules or rigs - unless you really have nothing else at all that you could fit there - that affect the same stat is fairly pointless, as your benefit is so tiny.

What suffers stacking penalties?

1. Absolute effects are never stacking-penalized, only percentage effects. That is to say, things like +1 warp core strength, +1000 structure HP, +15 m signature radius, +400 GJ capacitor are not stacking-penalized because they are not percentage (%) effects.
2. Only modules, rigs, Leadership-category skills (such as Skirmish Command), and Warfare/Mining Links are stacking-penalized. Non-Leadership skills, ship bonuses from ship skills, implants, hardwirings, and boosters (such as Synth Blue Pill, Strong X-Instinct, and others) are not stacking penalized.
3. Negative and positive effects are stacking-penalized separately. So, one +% and one -% effect to an attribute suffers no penalties, whereas with two +% and two -% effects, one of each would only be 86.9% effective. An example might be velocity modifiers: if you have one Overdrive Injector System on your ship (to increase your speed) whilst at the same time being slowed by a single Stasis Webifier from an enemy ship - both velocity modifers are 100% effective. If you are then affected by second Stasis Webifier (from the same or another ship) that second web will be only 86.9% effective.

It can be hard to tell exactly what suffers stacking penalties and what does not. For instance, the Overdrive Injector System II gives +12.5% velocity at a cost of -20% cargo capacity, and the description claims it suffers stacking penalties. The velocity bonus is stacking-penalized, but the cargo drawback is actually not. Similarly, the Warp Core Stabilizer II gives you one extra warp core strength at a cost of -40% targeting range and -40% scan resolution. It doesn't mention stacking penalty in the description, but the drawbacks are actually stacking-penalized.

We can learn from this that it is not the module itself which determines whether its effects are stacking-penalized, but rather the attribute affected.

Assuming the attribute they affect is actually stacking penalized, warfare link modules are stacking penalized as normal, along with the rest of your modules and rigs.

Here's a handy table of what ship effects are stacking-penalized and which aren't; there are some weird exceptions which are further discussed below the table. Remember, it is only percentage effects from modules/rigs that are penalized.

Is <insert attribute> stacking-penalized?

Ship attribute	Stacking-penalized
Powergrid (including reduced-PG-need effects)	no
CPU (including reduced-CPU-need effects)	no
Cargo capacity	no
Capacitor capacity	no
Capacitor recharge rate	no
Module capacitor use	no
Shield recharge rate	no
Shield / armor / hull hit points	no
Shield / armor / hull resistances	yes
Shield boost / armor repair bonus	yes
Sensor strength	yes
ECM jammer strength	yes
Scan probe sensor strength	yes
Scan resolution	yes
Targeting range	yes
Signature radius	yes
Velocity	yes
Inertia modifier (agility)	yes
Mass	yes
Duration (cycle time) bonuses (except weapons)	no
Missile launcher rate of fire	yes
Missile damage	yes
Missile explosion velocity	yes
Missile explosion radius	yes
Missile flight time	yes
Missile velocity	yes
Turret rate of fire	yes
Turret damage modifier	yes
Turret tracking speed	yes
All optimal range (modules/turrets)	yes
All falloff (modules/turrets)	yes
Mining laser yield (including mining drone yield)	no
Drone damage	yes
Salvaging probability	no

See also

• Module Stacking and Speed Modules.