Calculate BMI percentile for children and teens ages 2-19 using CDC growth chart standards.
Adult BMI uses the same cutoffs for everyone: under 18.5 is underweight, 18.5-24.9 is normal, 25+ is overweight. Children's bodies are different. A healthy amount of body fat changes dramatically as kids grow, and it differs between boys and girls. A 10-year-old boy and a 16-year-old girl with the same BMI number are in completely different situations.
That's why the CDC uses age-and-sex-specific percentiles for children ages 2-19. Instead of asking "is this BMI number high?", the question becomes "is this child's BMI higher or lower than most children the same age and sex?" The percentile tells you where your child falls relative to the reference population from CDC growth charts.
Below 5th percentile: Underweight. The child's BMI is lower than 95% of peers. May indicate nutritional issues, especially if the child has dropped percentiles over time. Worth discussing with a pediatrician.
5th to 84th percentile: Healthy weight. This is the target range. A child at the 50th percentile is exactly average. Being at the 20th or 75th is equally healthy. What matters more than the exact number is consistency: a child who has always tracked along the 30th percentile is growing normally.
85th to 94th percentile: Overweight. The child's BMI is higher than 85-94% of peers. This doesn't automatically mean there's a problem, especially in athletic or muscular children, but it's worth monitoring growth trends over time.
95th percentile and above: Obese. Clinical obesity in children is defined at the 95th percentile. This increases risk for type 2 diabetes, high blood pressure, asthma, sleep apnea, and joint problems. A pediatrician can assess whether the BMI reflects excess body fat or is influenced by muscle mass and body type.
BMI is a screening tool, not a diagnostic test. It can't distinguish between fat and muscle. A stocky, muscular child may have a high BMI percentile despite being perfectly healthy. Similarly, a thin child with low muscle mass might have a "normal" BMI but poor overall fitness.
The most valuable information comes from tracking BMI percentile over time, not from a single measurement. A child who has consistently been at the 70th percentile is growing normally. A child who jumps from the 50th to the 90th percentile in a year warrants attention. Your pediatrician tracks this on growth charts at every well-child visit.
For adult BMI, use our standard BMI Calculator. For a deeper dive into what BMI means and its limitations, see our BMI chart and healthy weight guide.
A single BMI measurement is less important than the trend over time. Your pediatrician plots your child's BMI on a growth chart at every well-child visit and looks for patterns. A gradual, consistent trajectory along any percentile line is normal. What raises flags is a sudden jump across percentile lines, either up or down, which can indicate changes in eating habits, activity level, or underlying health issues.
If your child is above the 85th percentile, your pediatrician will assess whether the BMI reflects excess body fat or is influenced by muscle mass and body frame. They may recommend dietary adjustments, increased physical activity, or further evaluation depending on the child's overall health picture. The goal for overweight children is usually to slow weight gain while the child continues to grow taller, not to put a child on a restrictive diet.