Board Thread:Game Discussions/@comment-217.42.230.51-20140607221539/@comment-24571857-20140608031732

Assuming Max guild bonuses

(Armor Stat + 316 (level 100 knight stat)) * (1.2 For Dual Element armor, 1.1 for Mono) * (1.05 HC Bonus) should get you the right answer. The number is always rounded up so if its 2399.12 it'll come out to 2400 in-game. Do it for Attack and Defense individually.

The question you have, the +13 atk would go to the Armor Stat.