The short answer
BMI only considers your height and weight, while a DEXA scan measures your actual body composition—how much of you is fat, lean tissue and bone, and where it is.
Two people can have exactly the same BMI and very different body fat levels, muscle mass and metabolic profiles. That is why BMI can label a muscular athlete “overweight” while missing someone with a “normal” BMI who carries high body fat and low muscle—sometimes called “skinny fat.”
When BMI is useful—and when it is not
BMI is a quick population screening tool. It is free and easy, but it cannot distinguish muscle from fat, cannot tell you where fat is stored, and cannot track changes in body composition. A DEXA scan can do all three, making it far more useful for individuals who want to measure real progress.
Related questions
Body Fat USA offers $85 DEXA body composition scans and $100 RMR metabolic tests in Denver (both for $175), with reports emailed in about 5 minutes. See all FAQs
