Ok so this is more of a question. Let's take someone my height, 5'4". Pick ANY BMI calculator out there and 107.5 lbs is 18.5, or the lowest weight in the "normal" range. Google "How much should I weigh chart" and 99% of the charts have the lowest recommended weight at 114 lbs for small frame.

It's been years without a satisfying answer. Why the difference? And is 107.5-114 healthy or not? I'm just really curious

I think it all depends on your build and the look you're going for. I kind of think going for the absolute lowest weight in the healthy range is sort of playing with fire and most people I know who are my height (and yours) would look positively gaunt at 107.5 lbs. To each their own though but I'd talk to my doctor about what he/she thinks is a healthy weight for YOU.

Keep in mind that BMI doesn't really take muscle mass into consideration, just height and weight. BMI charts are a guideline. We had a problem with this when I was in the military; a lot of really beefy dudes were failing their weight limits because of their muscles. There are other tests you can take to see where you fall on the BMI scale. In high school I was 5'10" and 117lbs., which according the charts put me at BMI 16.8. That sounds severely underweight, but I didn't look rail thin. I just looked thin. I still had a pretty good shape and pretty big bust. I ate normally and was pretty active. I was healthy. I never really cared for BMI charts because of that. I use them as a guideline, but even now I don't put too much stock in them. I think whatever is healthy is what you can easily sustain. If you get down to 107lbs., but can't sustain it, then you're just setting yourself up for failure.

For five foot two...
5 foot 2: 104 to 136

I made my goal the high end and my Doc said absolutely not! That 150 is what I should be aiming for. That 135-136 would be underweight.

What did the doctor base that on, though?

I'm 5-5 and my lowest adult weight was 135.... I looked and FELT sick. At the time I was working 40 hours a week, going to college full time AND babysitting for an alcoholic into the wee hours of the morning. I was exhausted.

I can't even imagine going below 120.

I met recently with my doctor and separately with a registered dietician. My doctor says that while a BMI of 18 is ok "on the charts" that for most people, especially women, under no circumstances should they go below 20.

The dietician told me that I am at an ideal weight which is 117 on a 5'1" frame which puts me at a BMI of 22.1.

I should probably point out again that my 117lbs. was in high school... There is no way I could sustain that now. I was able to sustain 147 for many years before I started porking out leading me to my current size. I'm aiming for 155 now since I'm older now than I was then and I think I could comfortably sustain that. If you have the willpower and self control you can get as low number-wise as you want; but if you can't sustain it, it's pointless.

I really don't put much stock in BMI guidelines at all. Muscle weight vs. fat weight and all that, plus the lines for "underweight" and "overweight" are very arbitrary and vary even by country.

All my life while eating and exercising normally, not worrying about my weight, I've weighed around 110 at about 5'6", which I think by BMI conventiosn is deemed underweight, and I have always been in perfect health. A couple years ago I got sick and totally unintentionally went into the 90's, and I stopped getting my period and was obviously to myself underweight/underfat, as was confirmed by my doctor. So by experience, I know that once I get too close to 100 it's too low. Obviously it will depend on what my body fat level is at that point, but it's just a general personal guideline.

Everyone's different!