Body mass index compares weight with height. It is convenient for broad screening, but it does not directly measure body fat or diagnose health.

Use BMI as one piece of information

For most adults, commonly used categories define a BMI below 18.5 as underweight, 18.5–24.9 as the standard healthy range, 25–29.9 as overweight, and 30 or higher as obese. These categories are population-level screening thresholds, not a complete personal assessment.

Know the limits

BMI cannot distinguish muscle from fat. It also does not show where body fat is carried, and health risk can occur at different thresholds for some ethnic backgrounds. Age, pregnancy, medical history and body composition can change how useful the number is.

  • Do not use an adult BMI calculator for children or teenagers.
  • Treat an unexpected result as a reason to seek context, not as a diagnosis.
  • A qualified professional can interpret weight alongside other health measures.

Focus on patterns you can sustain

Food quality, regular activity, sleep, stress and access to care all matter. A single measurement should not overshadow the habits and circumstances that shape long-term health.

Remember: This guide provides general education and is not a substitute for advice from a qualified health professional.