Every time Jax attacks an enemy he gains 3.5-11% increased attack speed for 2.5 seconds. The percentage is increased every 3 levels (which is at level 1 / 4 / 7 / 10 / 13 / 16). This effect stacks up to 8 times for a maximum of 28-88% bonus attack speed (depending on level) and will still stack if the attack is dodged or missed due to blind.

Stacks fall off one at a time every 0.25 seconds after not attacking for 2.5 seconds.