BMI Calculator
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.