BMI Calculator for Kids & Teens

BMI	Category
Below 18.5	Underweight
18.5 – 24.9	Normal weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity class I
35.0 – 39.9	Obesity class II
40.0 and above	Obesity class III

Formula	Same as adult BMI
Interpretation	Age- and sex-specific percentiles
Reference	CDC / WHO growth charts
Adult bands	Do not apply under 20

What is BMI for Kids & Teens?

Children's bodies change shape and composition constantly, so a single BMI threshold cannot work across ages. Paediatric practice uses BMI-for-age percentiles: a child's BMI is plotted against a reference population of the same age and sex, and the percentile — not the raw number — determines the category. A BMI that would be 'overweight' in an adult can be entirely normal at the peak of a growth spurt. This calculator gives the raw BMI and flags that a CDC or WHO growth chart is needed for interpretation. Always discuss a child's growth with a paediatrician rather than acting on a number alone.

Common Uses for BMI for Kids & Teens

Compute a child's raw BMI before plotting it on a growth chart
Understand why the adult bands do not apply to children
Prepare BMI values for a paediatric appointment

Frequently Asked Questions

Why can't I use the adult BMI categories for my child?

Because normal body composition changes with age and differs by sex during growth. A paediatric percentile chart accounts for that; the adult 18.5–24.9 band does not.

What percentile is a healthy BMI for a child?

For children aged 2–19, a BMI between the 5th and 85th percentiles is generally considered healthy. Below the 5th is underweight, 85th–95th overweight and above 95th obesity, per CDC definitions.

Should I put my child on a diet based on BMI?

No. Children should not be put on restrictive diets without medical supervision. If you are concerned about growth, speak to a paediatrician or dietitian.