Magic Penetration lower than what it should be (bug)

GanthorIII·3/9/2016, 7:17:42 PM·1 votes·545 views

if you have piercing thoughts masteries at max it is 7% magic penetration. if you buy void staff thats 35% magic penetration. total should be 42% but you only get 40%. it is only this combination though. because when you start you have 7% magic pen and if you dont have these masteries on then void staff gives 35% magic pen

2 Comments

Zombiemaster3/9/2016, 8:59:58 PM1 votes

It's actually not a bug. % penetration doesn't stack additively, it stacks multiplicatively. It's not simply just 7% plus 35%.

The actual formula is 1 - [(1 - .07) * (1 - .35)], which equals .3955, or 39.55%, which the game rounds up to 40%.