This calculator, designed and constructed by @astrology-addict, uses the method created by @geministereo as described here and quoted below.
Ever wondered why everyone says they're Aquarius dominant? That's because most people use the calculator on astro.com to determine their dominants. Unfortunately, this isn't the most accurate system because it weighs generational dominance (meaning outer planets) over personal dominance. So, pretty much everyone who has Uranus and Neptune in Aquarius thinks they're Aquarius dominant.
But are they really most like the sign of Aquarius? Chances are, no. They won't really relate to Aquarius if they do not have any personal Aquarius or 11th house planets. Their entire generation will. But "Aqua dom" is practically in everyone's tumblr bio as if it is a personal thing.
I think personal planets should be taken into account a lot more when determining dominants. That's why I created this system here - in hopes of calculating dominants realistically so everyone can relate to them more - and so dominants can more accurately depict your personality!
*DISCLAIMER* This is my personal idea of how dominants should be calculated so to better represent personal planets, and I realize that it is not the traditional way to calculate them.