BMI screens populations. Body fat percentage measures individuals. Both have a place — the trick is knowing which to weight when they disagree.
Sedentary or average-activity adults with typical muscle mass — BMI usually agrees with body-fat measurements within a couple of categories.
As a fast screen before a doctor's visit.
Athletes, lifters, or anyone who trains consistently. BMI cannot distinguish 20 lbs of muscle from 20 lbs of fat.
Older adults with sarcopenia — a "normal" BMI can hide low muscle and high fat (skinny-fat).
Get your body-fat estimate with the U.S. Navy method.
Body Fat Calculator →
BMI can label muscular athletes as overweight or obese. Here's when BMI misses the mark and what to use instead.
The clearest waist guideline for women, based on the NHS and Ashwell Waist-to-Height ratio — no charts, just one rule.
How age changes your healthy weight range, and the simple WHO/CDC formula that answers "how much should I weigh?".