Cooldown Reduction (abbreviated as CDR) is a champion statistic that reduces the cooldown of abilities, or the amount of time before an ability can be used again after activation, by a percentage. There are some items that separately reduce the cooldown for summoner spells or item active abilities, but do not grant cooldown reduction.
Cooldown reduction can be granted by items, 
buffs, runes, and masteries. CDR stacks additively and is capped at 40%, which can be increased to 45% with the 
Intelligence mastery.
Cooldown reduction is determined at the moment an ability is activated. Increasing/decreasing cooldown reduction while the skill is on cooldown will not affect the cooldown.
Cooldown reduction does not apply to:
- Static cooldowns
- Item active abilities (e.g.
Locket of the Iron Solari) - Item passive effects with cooldowns (e.g.
Guardian Angel) - Summoner spells. Ionian Boots of Lucidity provides a separate cooldown reduction for spells.
Although not a basic item, 
Fiendish Codex is the item from which the cooldown reduction gold value of 
24.75 per % cooldown reduction is derived.
Sources
- Items
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- Runes
Champion Abilities
Some champions have abilities that decrease their cooldowns by a flat amount, either their base cooldown or current cooldown, or entirely refresh their cooldown. Base reduction occurs before cooldown reduction takes effect while flat reduction occurs after cooldown reduction takes effect. By using those, a champion can circumvent the 40% cooldown reduction cap.
- Depending on built-in reduction type:
- Base (applies before CDR)
- Flat (applies after CDR)
- Percent (applies to base / current / total cooldown)
- Refresh (cooldown is immediately reduced to 0)
Base reduction
- Darius' Crippling Strike base cooldown is halved if it kills the target.
- Hecarim's Rampage base cooldown is reduced by 1 second if it hits a target, stacking up to 2 times.
- Kindred's Dance of Arrows base cooldown is reduced to 4 / 3.5 / 3 / 2.5 / 2 seconds while casting inside of Wolf's territory.
Flat reduction
- Amumu's Tantrum cooldown is reduced by 0.5 seconds each time Amumu is hit by an attack.
- Ezreal's Mystic Shot reduces all of Ezreal's cooldowns by 1 second if it strikes an enemy unit.
- Gragas' Body Slam cooldown is reduced by 3 seconds if it hits an enemy unit.
- Graves' Quickdraw cooldown is reduced by 1 second for every autoattack.
- Karma's Mantra cooldown is reduced by Error: Parameter '3' is not accepted. seconds every time she damages an enemy champion with an ability, and by Error: Parameter '3' is not accepted. seconds for a basic attack.
- Katarina's Voracity reduces all her abilities' cooldowns by 15 seconds whenever an enemy champion dies within 3 seconds of Katarina dealing damage to them.
- Lucian's Relentless Pursuit cooldown is reduced by 1 second for each of Lightslinger's strikes, and by 2 seconds against champions.
- Master Yi's Alpha Strike cooldown is reduced by 1 second for every autoattack.
- Miss Fortune's Strut cooldown is reduced by 2 - 1.1 seconds by marking a new target with Love Tap.
- Nocturne's Umbra Blades innate cooldown is reduced by 1 second for every autoattack.
- Olaf's Reckless Swing cooldown is reduced by 1 second for every autoattack.
- Undertow cooldown is reduced by 4.5 seconds if he manages to pick up his axe after using the ability.
- Shyvana's Twin Bite cooldown is reduced by 0.5 seconds for every autoattack.
- Skarner's Crystal Slash cooldown is reduced by 0.5 seconds for each successful autoattack, and by 1 second against champions.
- Syndra's Force of Will cooldown is reduced by 1 second if she throws the Template:Moi.
- Taric's Bravado's basic attacks reduce the cooldowns of his basic abilities by 1 - 0.55 seconds, increased to 6 - 3.3 seconds for Starlight's Touch's recharge time.
- Thresh's Death Sentence cooldown is reduced by 3 seconds upon hitting an enemy.
- Tryndamere's Spinning Slash cooldown is reduced by 1 second for every critical strike.
- Xin Zhao's Three Talon Strike reduces his other abilities' cooldowns by 1 second for each strike (for a maximum of 3 seconds reduction).
- Zed's Living Shadow cooldown is reduced by 2 seconds when his hits an enemy champion.
- Ziggs' Short Fuse innate cooldown is reduced by 4 seconds whenever he uses an ability.
- Zilean's Rewind on activation, reduces all of Zilean's other basic abilites' cooldowns by 10 seconds.
Percentage reduction
- Gnar's Boomerang Throw cooldown is reduced by 45 / 50 / 55 / 60% if he can catch it when its return (scales with GNAR!'s level).
- Boulder Toss cooldown is reduced by 60% if he picks up his boulder after using the ability.
- Master Yi's Highlander's passive component allows him to reduce the current cooldown on all of his basic abilities by 70% for every kill or assist he scores.
- Nidalee's Pounce base cooldown is reduced by 70% while it's currently higher if it kills a unit, or if Pounce hits an enemy marked as Hunted.
- Sona's Crescendo decreases cooldowns of her basic abilities by 10 / 25 / 40%.
- Yasuo's Steel Tempest's cooldown is reduced by 1% for every 1.6725% bonus attack speed he has.
Cooldown refreshing
- Diana's Lunar Rush cooldown is refreshed if the target is afflicted with the Moonlight debuff from Crescent Strike.
- Darius' Noxian Guillotine (rank 3) cooldown is refreshed if it kills enemy champion.
- Draven's Blood Rush cooldown is refreshed if Draven catches a Spinning Axe.
- Evelynn's Dark Frenzy cooldown is refreshed if Evelynn gets a champion kill or assist.
- Irelia's Bladesurge cooldown is refreshed if it kills a unit.
- Kalista's Rend cooldown is refreshed if it kills at least one target.
- Kha'Zix's Evolved Wings cooldown is refreshed if Kha'Zix gets a champion kill or assist.
- Ryze's Overload cooldown is refreshed by using his other abilities.
- Tristana's Rocket Jump cooldown is refreshed whenever Tristana gets a champion kill or assist.
- Twitch's Ambush cooldown is refreshed if an enemy dies while affected by Deadly Venom.
Other cooldown reducing effects
Active Ability Items
- Ruby Sightstone's passive reduces active item cooldowns by 20%.
- Multiple copies of the same active ability item share a global cooldown.
- Purchasing yet another copy while the already owned ones are still on CD will make the newest one's sync up with the others'.
Summoner Spells
- Only affected by Insight and by Ionian Boots of Lucidity's passive.
| Offensive |  Ability power ·  Attack damage ·  Attack speed ·  Critical strike chance ·  Critical strike damage ·  Armor penetration ·  Magic penetration ·  Life steal ·  Omnivamp · Physical vamp ·  True damage
|
|---|---|
| Defensive |  Heal and shield power ·  Health ·  Health regeneration ·  Armor ·  Magic resistance ·  Tenacity ·  Slow resist
|
| Utility |  Ability haste ·  Energy ·  Energy regeneration ·  Mana ·  Mana regeneration  Movement speed ·  Range
|
| Other |  Experience ·  Gold generation
|