Are "chance to cast" stackable?

[Corpfox]

Example:
Dracul's Grasp
5% Chance To Cast Level 10 Life Tap On Striking

Exile Runeword
15% Chance To Cast Level 5 Life Tap On Striking

So, can it be: 20% chance to cast level 15 life tap on striking?

OR something else?

[mackscynox]

afaik they use a completely %100 chance value so they can proc at the same time (one overriding other) or only one of them proc or none.

also levels doesnot add to each other.

ex: assume it will proc if on the high side of %100
case 1
percentage1: %96, dracs proc, L10 LT
percentage2: %10, exile not

case 2
p1: %10, dracs not
p2: %86, exile proc, L5 LT

case 3
p1: %96, dracs proc, L10 LT
p2: %86, exile proc, L5 LT
in this case one will override other. so you will either get L5 or L10 LT in the end

some maths professor can give proper percentage of LT procing

[hubb]

CTC only stacks if the skill level is the same, i.e. equipping two items with 5% Chance To Cast Level 10 Life Tap On Striking would result in a 10% ctc level 10 Life Tap.

As mack said, in your case they're procced separately and you'll end with a 19.25% chance to case either or both.

[Mare Crisium]

Just to prove it, Craft a bunch of Hit Power items. All have CTC level 4 Frost Nova. Equip one, play for a while, then equip them all and notice the difference!