A BMI betwen 19 and 25 is considered "normal" by the WHO/CDC. Real BMI measurements (not the online calculators) take into acount muscle/fat ratio. Since muscle weighs more than fat, the online calculators will show a higher BMI for muscular people when really their BMI is lower.

Try this link: http://www.halls.md/body-mass-index/bmi.htm

You can see how you rate (obese, overweight, normal, underweigth) based on the WHO-CDC scale or on a newer scale the page creator (Steven Halls)
put together that takes into account height/age/sex.

I had a question for Dr. Halls because his scale showed me as minimally overweight when WHO-CDC showed my weight as within the normal range.

This was his reply to my question:

"I think that the CDC criteria of BMI=25=overweight,
is a little too high for women. I think it should be a little lower. ( and I think a BMI=25=overweight, is a little too low for men, and should be a little higher for men.)

So, with the CDC criteria, when your BMI is under 25, it will call you normal, perhaps flattering you, when you may actually be a little bit overweight. But the halls.md v2 criteria will call a woman of your age and height, as "marginally overweight' at a BMI of 23.5, (approximately). As you discovered no doubt, your weight of 151 lbs, is just 1 pound above that threshold.

Another fact at work in my calculation, is an adjustment
for women's height. On this page http://www.halls.md/body-mass-index/age.htm
near the bottom, it shows that taller women tend to have
lower median BMI levels than shorter women... so I
considered that to be an effect of leg-length, that
penalizes short women, and labels greater proportions
of short women as overweight, compared to tall women.
So, I added in a little adjustment, and in you case,
being 5' 7" or 170cm, my calculation lowers the BMI
threshold by nearly 1 unit, for a woman of your height.

Thus, for a taller woman, it does become possible for
the CDC criteria to be a little more flattering, more
lenient, than the halls.md definition.

But for shorter women, and most men, the halls.md
criteria are a little less likely than the CDC criteria
to label you as overweight, or marginally overweight.

You've therefore stumbled onto one of the little oddities
of my calculator... it may seem odd, on superficial
inspection. Actually, another place my calculator
seems odd, is in the transition years from teenage
to young adult criteria. You can see that, in the
graphs that appear near the top of the page
of the URL I gave you above. There's a little kink/plateau
in the "overweight" curve for young women,
where I try to never allow the "overweight" threshold to
drop below 25, as it joins up to the pediatric definitions, that peg age=18 - BMI=25 as international standard values.


Hope that explains things. If not, I'm always happy to
receive more feedback and rebuttal.
Steve Halls"

His explanation sounds good to me.

Hope some of this helped.
Barb