How BMI is calculated
BMI = weight (kg) ÷ height (m)². The standard adult categories are: under 18.5 underweight, 18.5–24.9 normal range, 25–29.9 overweight, and 30+ obesity range.
What BMI does and doesn't tell you
BMI is a quick population-level screen — it cannot distinguish muscle from fat, so athletes often score "overweight" while carrying little fat, and it can miss low muscle mass in older adults. Use it as one signal among many, and talk to a clinician about what it means for you personally.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5–24.9 is considered the normal range, but individual context matters — discuss your number with a healthcare provider.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so muscular people can register as overweight despite low body fat.
Does BMI differ for children?
Yes — children and teens use age- and sex-specific percentile charts, not the adult categories shown here.