What BMI does and doesn't tell you
Body Mass Index is your weight in kilograms divided by your height in metres squared. It's a fast population-level screen, but it can't tell muscle from fat — so very muscular people often read as "overweight" while looking lean. Use it alongside, not instead of, measures like waist circumference and body composition.
The standard categories
Under 18.5 is underweight, 18.5–24.9 is a healthy weight, 25–29.9 is overweight, and 30+ is classed as obese. If you want to change where you land, start with your calorie target.
Frequently asked questions
Is BMI accurate for athletes?
Often not — extra muscle inflates the number. Lifters and athletes should lean on body-fat and performance measures instead.
Does BMI differ for men and women?
The formula and adult categories are the same. Body-fat percentage, which differs by sex, is a more nuanced measure.