Board Thread:General Discussion/@comment-91.125.83.80-20130812135504/@comment-26026175-20150125014932

My gauntlets, boots, ring and necklace each has Fortify One-Handed of 28% each. A certain sword of mine with a base damage of 95 is turned into around 201-205, I can't remember.

So if you do the math, that's a difference of 212% which is also = 100% + 28% + 28% + 28% + 28%. So to answer your question, it just stacks by addition.