This chart shows effective Ability Efficiency for channeled abilities.
Ability Efficiency linearly affects the energy cost of Warframe abilities. All Warframes have a base Ability Efficiency of 100%; Ability Efficiency over 100% indicates a reduction of ability cost while Ability Efficiency below 100% indicates an increase in ability cost. The Arsenal will not display an Ability Efficiency above 175% because abilities cannot consume less than 25% of their base costs.
$ \text{Final Ability Cost}=\text{Ability Cost} * Max((200%-\text{Ability Efficiency}), 25%) $
Channeled abilities drain energy at a specified rate. Ability Efficiency affects the energy drained at each tick as expected, but because Ability Duration affects the amount of time between these ticks, the formula for effective Ability Efficiency for channeled abilities is as follows:
$ \text{Final Energy Drain}=\text{Energy Drain} * Max((\frac{200%-\text{Ability Efficiency}}{\text{Ability Duration}}), 25%) $
In the case of Ability Duration under 100%, Ability Efficiency above 175% is also taken into account, even though not depicted in the Upgrade-Menu. The final drain still cannot go below 25% of its base value. (See the graph on the right for examples.)
The in-game energy bar display is rounded down to the nearest whole number, but the costs of the abilities are not. This results in the discrepancies in the apparent cost of abilities with Ability Efficiency mods. For example, an ability with 25 energy base cost will cost 17.5 energy with maxed Streamline (+30%). If this ability is used multiple times in a row, it will appear to cost 18 energy, then 17 energy, then 18 energy, then 17 energy and so on.
Energy Drain for Toggled Abilities
Edit
Some abilities are toggled on and last until the user turns them off or runs out of energy, such as 
Hildryn's 
Haven or 
Chroma's 
Spectral Scream. Energy drain for these toggled abilities depends on both Ability Efficiency as well as Ability Duration. See the related section for a full explanation.
ModifiersEdit
Streamline, Fleeting Expertise, Blind Rage, the Arcane Enhancement 
Pax Bolt, and the positive Ability Efficiency Arcane Helmets stack additively. Stacking with Trinity Meridian Helmet or Ash Scorpion Helmet does not appear to follow this formula; this suggests stacking is different when you have a helmet that reduces Ability Efficiency.
ModsEdit
Fleeting Expertise, Streamline, and System Reroute reduce ability costs linearly based on the percentage shown on the mod card. Blind Rage, instead, increases ability costs.
ArcanesEdit
Pax Bolt is currently the only Arcane Enhancement that affects Ability Efficiency.
Arcane HelmetsEdit
Arcane Helmets also reduce (or increase) ability costs linearly based on the percentage shown on the helmet. The following helmets affect Ability Efficiency:
See alsoEdit
