I don't know wher eyou came up with that formula, but I would chuck it out a window if I were you. At 5'2" I have 104 pounds of lean weight. By your formula I should only weight 110 pounds. That would put me at 5% body fat which is physically impossible. You might want to get your body fat % tested to see how much you have of lean weight (not just muscle but bone, blood, organs and so on) then set your goal according to that. To get down to where you want you may have to start starving yourself in order to lose muscle mass and bone density, and that is far fro msafe or healthy.