How is Magic Pen calculated?

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Nzo

Senior Member

06-01-2011

Lets assume I have Sorcerer Shoes + Void Staff. Is flat MP calculated or is % MP calculated first?


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GoSu sAviOr

Senior Member

06-01-2011

% Reduction then Flat Reduction then Flat Pentration and finally % Penetration.

So for sorc shoes you'd bring down their total MR by 20 and then reduce that value by 40%. (55% if you have the talent in offensive)

So for example lets assume annie with magic pen reds/quints with at least 9 points in offensive for the MrP bonus and sorc shoes.

If the opponent has a base MR of 30. Then your static 15 from runes adds with your 20 from the boots giving 35 flat penetration total. This would reduce your opponents MR to 0 since penetration can't go negative.

Lets say the get a BV so now they have 80 MR.

80 - 35 = 45

45*.45 = 20 MR.

20/120 = 17% Damage Reduction

So with normal talents, runes, sorc shoes, and void staff you'll be doing 83% of your total damage to someone thinking they're safe because they bought a BV.


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Lvl 8 Psyduck

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Senior Member

06-01-2011

Quote:
This would reduce your opponents MR to 0 since penetration can't go negative.
r u sure about that cuz when i play eve and use 'e' on dragon i see his mr and def goes negative like -5 def -21 mr


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Suroboro

Member

06-01-2011

don't quote me but I think armor and MR can go negative, but i've only seen it effect physical damage.


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Sykomyke

Senior Member

06-01-2011

Quote:
Originally Posted by tOxDeLivER View Post

So for sorc shoes you'd bring down their total MR by 20 and then reduce that value by 40%. (55% if you have the talent in offensive)
49% actually. The 15% from Archaic Knowledge + 40% from Void Staff is multiplicative, not additive.


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w3ak

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Senior Member

06-01-2011

% penetration is hard-capped at 49%

Also, it goes in this order:
Reduction (such as abyssal)
Penetration (flat) (such as sorc's)
% Penetration (such as void)


Note that only REDUCTION can bring MR or ARMOR Below 0.
As it is calculated first, there are very few situations in which this will occur (I think eve's skill reduces MR/armor, and same with kogmaw?).


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malphismia

Senior Member

06-01-2011

there's a few more champs that can reduce MR/AR below 0.

Corki + Black Cleaver + Starks.
Soraka.
Fiddle.
Amumu.
Rammus.

That's all that I can think off the top of my head.


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JohnCataldo

Senior Member

06-01-2011

Quote:
Originally Posted by elBOOBOO View Post
r u sure about that cuz when i play eve and use 'e' on dragon i see his mr and def goes negative like -5 def -21 mr
Reduction can go below zero.

Penetration can't.

They are different.


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Nzo

Senior Member

06-01-2011

so basically any flat MP isn't worth it aside from runes for early harass... in which case AP might be better.

sorc shoes become worthless, or not as viable as merc threads, late game when everyone has 100+ MR


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GoSu sAviOr

Senior Member

06-01-2011

Quote:
Originally Posted by Sykomyke View Post
49% actually. The 15% from Archaic Knowledge + 40% from Void Staff is multiplicative, not additive.
Whoops, good catch.