Cooldown Reduction / Ability Haste Calculator

Understanding the cooldown reduction and ability haste calculator — concept and principle

Cooldowns limit how often you can use an ability. Games express cooldown modifiers in two ways: older systems use a flat percentage of cooldown reduction (CDR), while League of Legends since its 2021 season uses ability haste (AH). This calculator turns either value into the final cooldown, the equivalent percentage reduction and the number of casts per minute.

Each star is one cast; 60 haste fits 8 casts into the minute instead of 5.

How it is calculated

With ability haste: final cooldown = base cooldown × 100 ÷ (100 + AH). Equivalent CDR = AH ÷ (100 + AH) × 100.
With percent CDR (any value above 0 overrides haste): final cooldown = base × (1 − CDR ÷ 100).
Casts per minute = 60 ÷ final cooldown.

Cooldowns are in seconds.

The principle

Ability haste is defined so that each point adds the same amount of ability uptime. With 100 haste you cast twice as often as with none, with 200 haste three times as often; casts per unit time grow as (100 + AH) ÷ 100, a straight line. The matching percentage reduction, AH ÷ (100 + AH), therefore rises with diminishing returns: 100 AH equals 50% CDR and 200 AH equals about 66.7%. Percentage CDR works the other way: each extra percent removes a fixed share of the base cooldown, so its value per point grows as you approach 100%, which is why games using it imposed a cap.

Worked example

Inputs: base cooldown 12 s, ability haste 60, % CDR 0 (so haste is used).
Final cooldown = 12 × 100 ÷ (100 + 60) = 1,200 ÷ 160 = 7.5 s.
Equivalent CDR = 60 ÷ 160 × 100 = 37.5%.
Casts per minute = 60 ÷ 7.5 = 8.

Each point is the calculator re-run with only “Base cooldown (s)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Base cooldown (s)	Final cooldown (s)
3	1.875
6	3.75
9	5.625
12	7.5
15	9.375
18	11.25
24	15

How to read the result

Compare casts per minute rather than seconds saved: going from 0 to 60 haste raises casts per minute from 5 to 8, a 60% increase, exactly matching the haste value. Every 10 haste adds 10% more casts no matter how much you already have, so haste never becomes more or less efficient per point. Real uptime is lower than the theoretical number because casting time, travel and waiting for targets add delay.

Common mistakes

Adding ability haste and percent CDR together; they are different scales.
Thinking 100 ability haste removes the cooldown; it halves it.
Forgetting ability-specific reductions, such as cooldown refunds on kills, which this calculator does not include.

Keep in mind: The haste formula follows League of Legends; other games may use different constants, caps or stacking rules. Check the current game documentation, since values change with patches.

Frequently asked questions

How much ability haste equals 40% CDR?

Solve AH ÷ (100 + AH) = 0.4, which gives AH ≈ 66.7.

Is there a cap on ability haste?

The formula has no mathematical cap, because cooldown approaches zero only as haste grows without limit.

Does haste affect summoner spells or items?

In League of Legends only specific sources affect those, such as summoner spell haste and item haste; normal ability haste does not.

Sources: League of Legends Wiki, "Ability haste" and "Cooldown reduction" articles

Checked 8 Nov 2026. Official league / federation formulas where they exist; widely used community formulas otherwise. For fun and analysis — not betting advice.

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