What is Ability Haste in League of Legends?

Ability haste is a stat in League of Legends that reduces the cooldown of abilities. The more ability haste a champion builds, the faster their abilities will come off cooldown, allowing them to cast spells more frequently.
Unlike cooldown reduction which was capped at 40%, ability haste has no cap, meaning players can stack as much of it as they want to reach very high casting speeds. Building a lot of ability haste enables champions to spam their abilities much more often than normal in fights.

How does Ability Haste work?

Ability haste is simply calculated into cooldown reduction and your cooldown time is lower. The difference is that the more ability haste you have, the less cooldown reduction it gives. Going from 0 to 10 ability haste reduces cooldowns by 10%, but going from 90 to 100 ability haste is going to be way less than 10%.

That's the point of ability haste existing - instead of having a cap, you can still stack cooldown reduction items, but each one gives you less value. So 0-10 ability haste reduces cooldowns by 10%, but as you stack more, each additional point reduces cooldowns by progressively smaller amounts. This allows ability haste to scale infinitely rather than being capped.

How much Ability Haste can you have?

There is technically no cap on how much you can stack. At 100 ability haste, your cooldowns would be reduced by 50%, greater than the 40% cap from cooldown reduction. It is possible to reach 100 ability haste in a normal build.

Ability haste values on items tend to range from 10 to 30. Below is a list of items that give you ability haste: