Body Mass Index shows up on medical forms and fitness apps constantly, but the number alone does not tell the whole story.
How BMI is calculated
BMI is weight in kilograms divided by height in meters squared, or weight in pounds divided by height in inches squared multiplied by 703. It is a simple ratio, not a direct measurement of body fat.
What the standard ranges mean
The commonly used ranges are under 18.5 for underweight, 18.5 to 24.9 for normal weight, 25 to 29.9 for overweight, and 30 or above for obese. These bands are population level guidelines, not individual diagnoses.
Where BMI falls short
BMI does not distinguish between muscle and fat, which is why athletes with high muscle mass often show as overweight despite low body fat. It also does not account for age, sex, or where fat is distributed on the body.
Using it as one data point
Check the number with the BMI Calculator, but treat it as a starting point for a conversation with a healthcare provider rather than a complete health assessment.