BMI Calculator for Kids
BMI works differently for children and teenagers than it does for adults. Here is what parents need to know before using any BMI number for a child.
Children use percentiles, not fixed categories
For adults, a BMI of 25 always means “overweight.” For children and teens aged 2–19, the same BMI can be perfectly healthy or a concern depending on the child's age and sex, because body fat changes naturally as kids grow.
That is why paediatric BMI is expressed as a percentile — comparing a child to thousands of others of the same age and sex — rather than the adult bands.
BMI-for-age percentile categories
| Percentile | Category |
|---|---|
| Below 5th | Underweight |
| 5th – 84th | Healthy weight |
| 85th – 94th | Overweight |
| 95th and above | Obese |
Based on CDC growth charts for ages 2–19.
How to get a child's BMI percentile
Calculating a child's BMI uses the same formula as adults (weight ÷ height²), but the result must then be plotted on an age- and sex-specific growth chart to find the percentile.
Because that requires official growth-chart data, use the CDC or WHO children's BMI tool, or ask your paediatrician. Do not rely on an adult BMI calculator to judge a child's weight.
Frequently asked questions
Can I use an adult BMI calculator for my child?
No. Adult BMI categories do not apply to children. Kids need a BMI-for-age percentile from a paediatric growth chart, available through the CDC, WHO or your doctor.
What BMI percentile is healthy for a child?
A BMI between the 5th and 84th percentile for the child's age and sex is considered a healthy weight.