BMI (Body Mass Index) is a simple screening number that uses your height and weight to flag whether you may be underweight, in a healthy range, overweight, or obese. The CDC uses BMI as a population-level screening tool — it is not a diagnosis, but it is a good starting point for a conversation with a clinician.
How BMI is calculated
The metric formula is BMI = weight (kg) ÷ height (m)². Categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and over obese. The same number does not mean the same thing for very muscular athletes or very short or tall adults — treat the categories loosely.
Worked example
A person 1.75 m tall weighing 72 kg has a BMI of 72 ÷ (1.75 × 1.75) = 23.5, which falls in the normal range.
