Child BMI Calculator (Ages 2–20)
Calculate your child's BMI-for-age percentile using CDC growth chart standards. Unlike adult BMI, children's BMI is interpreted relative to other children of the same age and sex. Enter your child's age, height, and weight to see their percentile and weight category.
Child BMI Results
CDC Weight Categories for Children
| Category | BMI Percentile | Action |
|---|---|---|
| Underweight | Below 5th percentile | Consult pediatrician — check nutrition |
| Healthy Weight | 5th to 84th percentile | Continue current habits; routine checkups |
| Overweight | 85th to 94th percentile | Encourage physical activity and balanced diet |
| Obese | 95th percentile and above | Consult pediatrician; comprehensive evaluation |
Healthy Weight Ranges by Age (Boys)
| Age | Healthy BMI Range | 5th–84th Percentile Weight Range |
|---|---|---|
| 5 years | 13.8–17.2 | 34–48 lbs / 15.4–21.8 kg |
| 8 years | 14.0–18.7 | 46–67 lbs / 20.9–30.4 kg |
| 10 years | 14.3–20.5 | 57–90 lbs / 25.9–40.8 kg |
| 12 years | 14.8–22.6 | 71–117 lbs / 32.2–53.1 kg |
| 15 years | 16.3–24.6 | 101–152 lbs / 45.8–69.0 kg |
| 18 years | 17.6–25.5 | 120–180 lbs / 54.4–81.6 kg |
Understanding Child BMI
BMI (Body Mass Index) = weight (kg) ÷ height² (m²). For children, this number alone is not enough — it must be compared to CDC growth charts that show the distribution of BMI among U.S. children of the same age and sex. This produces a percentile rank that indicates where a child falls relative to peers.
Why Age and Sex Matter
Children's body composition changes dramatically with age. A BMI of 17 is healthy for a 6-year-old but below average for a 16-year-old. Girls naturally have more body fat than boys at the same BMI. CDC growth charts account for these differences using age and sex-specific percentile curves.
Tracking Growth Over Time
A single BMI measurement is less informative than tracking trends at regular well-child visits. A child moving from the 60th to 85th percentile over 2 years is more concerning than a child consistently at the 85th percentile. Pediatricians typically plot BMI on growth charts at every annual visit.
Promoting Healthy Growth in Children
For children outside the healthy weight range, the approach differs from adult weight management. The primary goals for overweight children are often to slow weight gain rather than lose weight, allowing normal height growth to bring BMI percentile down naturally. Strategies include: increasing daily physical activity to at least 60 minutes, reducing screen time, encouraging regular family meals, emphasizing whole foods over processed snacks, and ensuring adequate sleep (sleep deprivation increases hunger hormones). Dieting or calorie restriction is rarely appropriate and can harm growth and development.
Frequently Asked Questions
Related Reading
Adult BMI uses fixed cutoffs regardless of age. Child BMI (BMI-for-age) uses percentile comparisons against children of the same age and sex. A BMI that is healthy at age 6 may indicate overweight at age 14. The same number means different things at different ages in growing children.
The CDC defines healthy weight as the 5th to 84th percentile. Underweight is below the 5th, overweight is the 85th to 94th, and obese is the 95th percentile or above. Being at the 50th percentile means the child's BMI equals the average for their age and sex.
Yes. BMI does not distinguish between fat and muscle. A heavily muscular child may have a high BMI percentile without excess body fat. This is one reason BMI is considered a screening tool rather than a diagnosis. Pediatricians consider activity level, body composition, and overall health alongside BMI.
The CDC recommends BMI screening for children starting at age 2. Before age 2, weight-for-length charts are used instead. Pediatricians typically assess BMI at every well-child visit from ages 2 onward and plot the results on growth charts to track trends over time.