From what I know if you look at your BMI range, it is the top figure weight, say in my case, 78 kg. You now take your current weight, which when I started surgery was say 128 kg. Sorry I work in Metric but it works the same in imperial. 128-78 equals 50 kg. That 50 kg is my XS weight, so if mini gastric bypass has a predicted loss of 70 to 85% of the XS weight then it is 70% of 50 kg to 85% of 50 kg. I.e 35 to 59.5 kg is what I am expected to lose with the procedure.
When it comes right down to it from what I understand. If like me, you have been obese all your life. Then you will have thicker, heavier bones to support that weight, more skin to wraparound it and a larger heart to pump blood around your body, so that means no matter what the general BMI limit is it is not totally relevant and there has been some suggestions by bariatric surgeons that to aim for a BMI of 30.
BMI is intrinsically a flawed concept as it does not take into account, body muscle mass. You will know the example of the brick **** house musclebound New Zealand rugby player with no fat, looking like a crazy obese person on paper because they have a BMI of 45.
I am 52 this year, so I think I would be happy with something above the BMI range. Otherwise my skin will waft in the breeze! ?