📊 BMI by Age Calculator

Body Mass Index (BMI) is a screening measure that uses height and weight to estimate body fatness. It is calculated as weight in kilograms divided by the square of height in metres. While widely used, it is a screening tool, not a direct measure of body fat or health.

In children and teens (age 2–19), body fat naturally changes as they grow, and boys and girls develop differently. Using fixed adult cutoffs would misclassify many healthy children. The CDC recommends BMI-for-age percentile charts, which compare a child's BMI to others of the same age and sex. For older adults (65+), research suggests slightly higher BMI may be protective against osteoporosis and frailty.

For children aged 2–19: below the 5th percentile = Underweight; 5th to below 85th percentile = Healthy Weight; 85th to below 95th percentile = Overweight; 95th percentile and above = Obese. This calculator uses a simplified lookup based on published CDC data.

BMI does not measure body fat directly. Muscular athletes may have a high BMI despite low body fat. It also does not account for fat distribution — abdominal fat is more dangerous than fat stored elsewhere. BMI should be used alongside waist circumference and other clinical assessments.

For adults 20+, the WHO defines: Under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. Some Asian populations use slightly lower thresholds (23 for overweight) due to higher health risks at lower BMI values.