Child & Teen BMI Calculator
Calculate BMI for children and teenagers aged 2 to 19. Because children's bodies change with age, the result must be interpreted using percentile growth charts.
How is child BMI different from adult BMI?
BMI is calculated the same way for children as for adults — weight divided by height squared — but it is interpreted completely differently. Children and teenagers are still growing, and their body composition changes naturally with age and differs between boys and girls. For this reason, a child's BMI cannot be judged against the fixed adult categories. Instead, it is plotted on age- and sex-specific percentile charts that compare the child to others of the same age and sex.
Understanding BMI percentiles
For children aged 2 to 19, health authorities use BMI-for-age percentiles. A percentile shows how a child's BMI compares to a reference population. Broadly, below the 5th percentile is considered underweight, the 5th to 85th percentile is a healthy weight, the 85th to 95th is overweight, and at or above the 95th percentile is obese. Because plotting on the official growth charts requires the child's exact age in months and sex, this is best done by a pediatrician. For a fuller explanation of how child and teen BMI percentiles work, see our guide to BMI in children and teenagers.
Why a doctor should interpret the result
This calculator gives you the BMI number, but turning that number into a meaningful assessment requires the official growth charts and clinical judgement. A pediatrician will plot the BMI on the appropriate chart, consider the child's growth pattern over time, and take into account factors like puberty, build and overall development. A single BMI reading is far less informative for a child than the trend across regular check-ups.
Supporting a healthy weight in children
If there are concerns about a child's weight, the focus should be on healthy habits for the whole family rather than dieting, which is generally not recommended for growing children without medical supervision. Encouraging balanced meals, plenty of fruits and vegetables, limiting sugary drinks and snacks, regular physical activity and good sleep all support healthy development. Always involve a pediatrician before making significant changes to a child's diet or activity.
Frequently Asked Questions
The calculation is the same as for adults — weight in kilograms divided by height in metres squared. However, the result for children aged 2 to 19 must be interpreted using age- and sex-specific percentile charts, not the fixed adult BMI categories, because children are still growing.
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Sources & References
- 1.Centers for Disease Control and Prevention (CDC). BMI for Children and Teens.
- 2.World Health Organization. Growth reference data for 5-19 years.
- 3.American Academy of Pediatrics. Body Mass Index (BMI) in Children.
LifeCheckIQ content is based on peer-reviewed research, recognised clinical guidelines, and authoritative medical sources, and is reviewed by Deborah Adotso, General Nurse, for clinical accuracy.
Medical Disclaimer: This tool is for informational and educational purposes only. Results are not a medical diagnosis. Always consult a qualified healthcare professional for medical advice, diagnosis, or treatment. In an emergency, call your local emergency number or visit the nearest hospital immediately.