http://www.abcbodybuilding.com/ultim...stingguide.php
Follow the guide at the bottom of that article EXACTLY. No questions asked.
As for BMI it is a travesty they use it. I am 12% bf and it says i'm obese. They don't account for muscle mass. It is really a marketing scam to scare the hell out of people so they hire personal trainers. I sugges tracking your bf%. Good luck.