Cooldown Reduction Calculator

Cooldown Reduction (CDR) in video games reduces the wait time between uses of abilities or skills. Two systems are in common use, and they behave in opposite ways once you stack them. Getting them mixed up is how people end up buying the wrong item.

Percentage CDR: Effective Cooldown = Base Cooldown × (1 − CDR%/100)

Ability Haste (the additive system): Effective Cooldown = Base Cooldown × 100 ÷ (100 + Haste)

Casts per minute formula: Casts Per Minute = 60 ÷ Effective Cooldown

What each variable means:

• Base Cooldown: the ability’s reset timer before any reduction (in seconds).
• CDR%: the total Cooldown Reduction percentage from items, talents, buffs, or character stats.
• Effective Cooldown: the actual time you wait between casts after CDR is applied.
• Casts Per Minute (CPM): how many times you can use the ability per minute; a key damage-per-second metric.

Worked example (League of Legends style): Ability base cooldown: 12 seconds. You have 30% CDR from items. Effective CD = 12 × (1 − 0.30) = 12 × 0.70 = 8.4 seconds Casts per minute = 60 ÷ 8.4 = 7.14 casts/min vs. 60 ÷ 12 = 5.0 without CDR.

Which system has diminishing returns? Neither, and that is the surprise

Almost every guide gets this backwards, so here are the numbers on a 12-second ability.

Percentage CDR, in seconds saved:

• 0% to 10%: 12.0s becomes 10.8s, saving 1.2s
• 30% to 40%: 8.4s becomes 7.2s, saving 1.2s

Identical. Percentage CDR is perfectly linear in seconds. But seconds are not what you care about. Casts per minute is what turns into damage, and there the same two steps look nothing alike:

• 0% to 10%: 5.00 casts/min becomes 5.56, a gain of 0.56
• 30% to 40%: 7.14 casts/min becomes 8.33, a gain of 1.19

The second ten points are worth more than twice the first ten. Percentage CDR has accelerating returns, not diminishing ones, and it runs to infinity as you approach 100%. That is exactly why every game using it slaps a hard cap on top, historically 40% in League of Legends.

Ability Haste is the fix for that problem. Run the same test:

• 0 to 40 haste: 5.00 casts/min becomes 7.00, a gain of 2.00
• 40 to 80 haste: 7.00 becomes 9.00, a gain of 2.00

Every point of haste buys exactly the same amount of casting, forever. That is what “additive” means here, and it is why haste needs no cap at all. Riot switched League of Legends from CDR to Ability Haste in the 2021 preseason for precisely this reason: the old system made the last few points absurdly strong and the cap did the balancing instead of the math.

Converting between the two

Haste = 100 × CDR ÷ (100 − CDR), and CDR = 100 × Haste ÷ (100 + Haste).

So the old 40% cap is 67 haste, and 40 haste is only 28.6% CDR. The result panel prints the equivalent for whatever you enter, which is handy when a wiki quotes one system and your game shows the other.

Hard caps: check your specific game. Percentage systems nearly always cap somewhere between 40% and 50%. Haste systems usually do not cap, though individual items still stop existing at some point.