Smart BMI Muscle-adjusted
BMI corrected for body composition — so muscle mass doesn't count against you.
Don't know your body fat? Estimate it from measurements
U.S. Navy method — measure the waist at the navel and the neck just below the larynx.
Why standard BMI fails lifters
Standard BMI treats a kilogram of muscle exactly like a kilogram of fat, so anyone carrying above-average muscle gets pushed into the "overweight" or "obese" category despite being lean and healthy. Smart BMI fixes this by splitting your weight into a fat-mass index (FMI) and a fat-free-mass index (FFMI), then answering a more useful question: what would your BMI read if you carried an average amount of muscle?
How to use it
Enter your body fat percentage if you know it. If you don't, expand the estimator and enter your waist, neck (and hip for women) — the calculator uses the U.S. Navy circumference method to estimate body fat for you. You'll get your muscle-adjusted BMI alongside your standard BMI, your FFMI (muscularity) and FMI (fat index).
Frequently asked questions
What is Smart BMI?
Smart BMI is your personal fat-mass index plus the average fat-free-mass index for your sex. In plain terms, it estimates what your BMI would be if your muscle mass were average — removing the penalty standard BMI gives to muscular people.
Why does standard BMI call me overweight when I look lean?
Because BMI only uses height and weight, it counts your extra muscle as if it were excess fat. Smart BMI separates the two, so a muscular build is no longer misread as overweight.
How do you estimate body fat without a scan?
If you do not enter a body fat percentage, the tool uses the U.S. Navy tape method, which estimates body fat from your height and a few circumference measurements (waist, neck, and hip for women).