BMI Calculator for Children
Track a child’s BMI with age, months and sex in context. For growing children, BMI is interpreted by age rather than with fixed adult BMI cutoffs.
Understanding BMI in children
Children are constantly growing. Height, weight, muscle, bone and body-fat levels change with age, so a child’s BMI should not be judged using the fixed adult ranges of underweight, normal weight, overweight and obesity.
Pediatric BMI is interpreted in relation to a child’s age and sex. The CDC describes child and teen BMI as a screening measure that uses sex-specific BMI-for-age percentiles for ages 2 through 19.
Why age and months matter
A BMI that may be typical at one age can have a different meaning a year later. That’s why pediatric BMI tools use the child’s exact age, including months, rather than applying a single adult threshold to everyone.
Child BMI-for-age percentiles
For children and teens 2–19, BMI is commonly interpreted with sex-specific BMI-for-age percentiles. The CDC calculator reports BMI, BMI percentile and BMI category and plots the result on a growth chart. citeturn1search0turn1search2
| Percentile position | General screening interpretation |
|---|---|
| Below 5th percentile | Underweight |
| 5th to below 85th percentile | Healthy weight |
| 85th to below 95th percentile | Overweight |
| 95th percentile or higher | Obesity |
These categories are screening classifications; they do not by themselves diagnose a health condition.
Growth is more important than a single number
Look at the pattern over time
One BMI measurement is only one point in a child’s growth story. A pediatric professional can look at growth over time, family history, development, physical examination and other relevant information.
Muscle and body composition matter too
BMI is based on height and weight and cannot directly distinguish fat from muscle. This limitation is especially relevant when a child’s body composition differs substantially from typical growth patterns.
WHO child growth standards
The World Health Organization provides child growth standards and BMI-for-age references. For children up to 5 years, WHO provides BMI-for-age growth charts for boys and girls, alongside other growth indicators. citeturn1search4turn1search7
WHO also notes that measurement method matters for young children: BMI-for-age references for birth to 2 years are based on length, so standing height and recumbent length may require appropriate conversion when applying the charts. citeturn1search7turn1search8
What parents should do with an unusual result
Don’t put a child on a restrictive diet or attempt rapid weight loss because of an online BMI result. If you are concerned about a child’s growth, weight, appetite or development, discuss the result with the child’s pediatrician or another qualified healthcare professional.