Mechanic of Dota: Attack speed

ALL ABOUT ATTACK SPEED

Attack speed is a measure of how fast units attack. In game, increased attack speed (IAS) is granted by items, buffs from spells and auras, Agility, and passive abilities.

Attack speed is represented in game as a number, usually with a percentage sign (%), but sometimes not. Regardless of whether a percentage sign is included or not, the attack speed acts the same.

Each point of Agility (either base Agility or extra Agility from items/abilities) increases IAS by 1.

All sources of IAS stack additively, if a hero has 30 Agility, a Hand of Midas, and is affected by a Shiva's Guard aura from an enemy unit, the hero will have 30+30-25=35 total IAS.

Every unit in the game has a Base Attack Time (BAT), this value cannot change. If a unit has no 0 IAS, it will have an amount of seconds between each attack equal to its BAT.

There is a maximum and minimum IAS a unit can have. A unit's IAS cannot go above 400 or below -80, if it would be reduced beyond these values, it will instead be capped at them.

Attack Speed Formula

To determine how fast a unit attacks, the formula below is used:

Attacks per second = (1 + IAS)/BAT

Note: IAS in this formula is a percentage, so you must divide your actual IAS by 100 before using it in this formula.

Example of formula:
Vengeful Spirit has a BAT of 1.7
If Vengeful Spirit has a total of 160 IAS, the formula will be as follows:
Attacks per second = (1 + 1.60)/1.7 = 1.53 times per second.

Special case: Damage point

If a unit's damage point (the point at which an attack completes) is greater than the unit's BAT, the damage point will be used instead of the BAT in the formula above.

The only unit in DotA that this is true for is the Death Ward.