Goal weight

How do you determine goal weight with your clients? Is it based on BMI? I ask because I was once smack in the middle of a normal BMI range for my height (I am 5’3″ and I was 123 lbs at the time). Size 2s were falling off me, I was shopping in the girls’ section and all of my bones were really sticking out. It was so weird, since according to the BMI calculations I was “normal,” but was clearly underweight. I am just starting out with my weight loss so this is not an imminent concern, but just was curious as to your process on how you advise your clients. Thank you!