Body fat percentage formula from body mass index

Body Fat percentage Formula

Comments and Admiration of their body fat percentage formula

The formula to predict your body fat percentage, based on your current BMI, age, and gender:

Child Body Fat % = (1.51 x BMI) – (0.70 x Age) – (3.6 x gender) + 1.4

Adult Body Fat % = (1.20 x BMI) + (0.23 x Age) – (10.8 x gender) – 5.4

where male gender= 1, female=0.

Well, this is just one possible body fat formula. Others exist1 from different authors, and some are specific to different races. But this formula is OK. But you should be aware that there is considerable variation in body fat percentage at any constant Body Mass Index.


  1. Jackson AS, Stanforth PR, Gagnon J, et al. The effect of sex, age and race on estimating percentage body fat from body mass index: the Heritage Family Study. Int J Obes Relat Metab Disord, Jun 2002;26(6):789-96

David David
Thanks. The formula was exactly what I…nevermind.

Gretchen Gretchen

David David
I realized, I’m too lazy to use it.


There is a problem with this formula, and others like it. They are linear.

Tyler Tyler
The straight lines. The pink one is from the formula on this page.

Various Body Fat versus BMI formulas

But Body fat percentage has a curved distribution relative to body mass index, not linear.
body fat versus BMI

Dr. Halls Dr. Halls
If you were a slim woman with BMI under 20, the pink line formula would say you had 25 to 30% body fat, which is totally wrong.

Talking Moose Talking Moose
I’d guess about 15 percent, from the curvy chart above.

Dr. Halls Dr. Halls
That formula is even on wikipedia. The world needs something better.

Betty Betty
That DOES make me mad, when I use online fat calculators.


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