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Can I get a red who knows about armor pen rules?

ZerglingOne·10/19/2016, 1:32:16 AM·1 votes·236 views

Because while % total armor pen is exceedingly rare as of right now, existing only in masteries and on Darius Gangplank these champions. The rules are not clear.

I understand that when you stack sources of % armor pen or bonus % armor pen, they stack multiplicatively. That is if I had 40% bonus armor pen and 20% bonus armor pen, that would be 52% bonus armor pen which is 1 - ( (.6) x (.8) ). That is perfectly clear for me.

The interaction however is very unclear when mixed with total % armor pen.

So there are two options here as I see it. There is the chance that they stack independently, that is.

  1. Effective armor = (total armor) - (total armor) x (% armor pen) - (Bonus armor) x (% bonus armor pen) In which case, the bonus armor gets double dipped by the different sources meaning they're additive.

OR

  1. Effective armor = (total armor) - (base armor) x (% armor pen) - (bonus armor) x (multiplicative % of total and bonus armor pen)

Please let me know. This is for a DPS calculator I'm writing.

6 Comments

WoonStruck10/19/2016, 1:34:40 AM1 votes

Penetration that applies to both base and bonus armor (including armor reduction taking first priority in all cases) apply first.

Bonus armor penetration would apply last.

If you already have them under their base armor by other means (excluding flat, which applies last), bonus armor pen would not apply. Essentially, base armor is not reduced until there is no more bonus armor to be reduced by something applied to both.

Flat penetration applies after everything else, making it and excessive % armor reduction (like black cleaver) the only way to reduce base armor.

% reduction>flat reduction>% pen>% bonus pen>flat pen