Calculate BMI for children ages 2–20 with CDC growth chart percentiles. Determine weight status using age-and-sex-specific pediatric standards.
The BMI Calculator for Kids determines your child's Body Mass Index and plots it against the CDC growth charts to find their age-and-sex-specific percentile. Unlike adult BMI, where fixed cutoffs define weight categories, children's BMI must be interpreted using percentiles because body composition changes dramatically during growth and differs between boys and girls at every age.
The Centers for Disease Control and Prevention (CDC) recommends using BMI-for-age percentile charts for children and teens aged 2 through 20 years. These charts are based on national survey data from the CDC's growth reference population and account for the natural changes in body fat that occur as children develop. A child at the 50th percentile has a BMI equal to or greater than 50% of children of the same age and sex.
Weight status categories for children are defined as: Underweight (below 5th percentile), Healthy Weight (5th to less than 85th percentile), Overweight (85th to less than 95th percentile), and Obese (at or above 95th percentile). These thresholds were established based on research linking specific percentile ranges to health risks in childhood and adolescence.
This calculator provides instant percentile estimation, healthy weight ranges for your child's height and age, and comparison to the 50th percentile reference — giving parents, pediatricians, and school nurses a quick, reliable assessment tool.
Monitoring your child's BMI percentile over time is one of the most effective ways to track healthy growth and catch potential weight problems early. Childhood obesity has tripled in the U.S. since the 1970s, and early identification allows for intervention when lifestyle changes are most impactful.
This calculator provides instant results that would otherwise require plotting on a paper growth chart or using clinical software. Parents can track their child's percentile between pediatric appointments, and healthcare providers can quickly screen patients during visits.
BMI = (weight in pounds / height in inches²) × 703 The calculated BMI is then compared against CDC growth chart LMS parameters for the child's exact age and sex to determine the percentile. Weight status categories: - Underweight: < 5th percentile - Healthy Weight: 5th to < 85th percentile - Overweight: 85th to < 95th percentile - Obese: ≥ 95th percentile
Result: BMI 16.9, approximately 55th percentile — Healthy Weight
A 10-year-old boy at 54 inches and 70 lbs has a BMI of 16.9. The CDC 50th percentile for 10-year-old boys is 17.1, so this child is near the 55th percentile, squarely in the Healthy Weight range.
The CDC growth charts used in the United States were published in 2000 and are based on data from five national health examination surveys conducted between 1963 and 1994. These charts represent how American children were growing during that period, serving as a reference for comparison rather than an optimal growth standard.
The data includes measurements from a large, nationally representative sample of children across diverse racial, ethnic, and socioeconomic backgrounds. The statistical method used (LMS method) smooths the distribution of BMI values at each age into three parameters — L (skewness), M (median), and S (coefficient of variation) — allowing precise percentile and z-score calculations.
Children's BMI typically decreases from age 2 to about age 5–6 (called adiposity rebound), then increases through adolescence. The age at which this rebound occurs is actually a predictor of later obesity: children who rebound earlier (before age 5) are more likely to have higher BMI in adolescence and adulthood.
During puberty, significant differences emerge between boys and girls. Boys tend to gain more lean mass, while girls naturally accumulate more body fat. This is why separate growth charts exist for each sex. A BMI of 22 might be 60th percentile for a 15-year-old boy but 70th percentile for a 15-year-old girl.
BMI is a screening tool, not a diagnostic test. It cannot distinguish between lean mass and fat mass. Children who are very muscular (often seen in athletic teens) may have elevated BMI without excess body fat. Conversely, a child with low muscle mass may have normal BMI but excessive body fat (sometimes called "skinny fat" or normal-weight obesity).
For a more complete assessment, pediatricians may evaluate waist circumference, skinfold thickness, diet quality, physical activity levels, family history, and blood tests (lipid panel, fasting glucose). BMI percentile provides the starting point for these clinical decisions.
Children's body fat changes as they grow, and boys and girls develop differently. A BMI that is normal for a 6-year-old may be overweight for a 14-year-old. Percentiles account for these age-and-sex-specific differences, whereas adult BMI uses fixed thresholds (18.5, 25, 30).
The CDC recommends routine BMI-for-age screening starting at age 2. For children under 2, weight-for-length charts are used instead. Pediatricians typically check BMI at annual well-child visits.
Yes, a BMI-for-age at the 90th percentile falls in the Overweight category (85th to <95th percentile). However, BMI alone doesn't distinguish between muscle and fat. Extremely athletic children may have a high BMI due to muscle mass. Your pediatrician can assess body composition in context.
A child below the 5th percentile is considered underweight. This could indicate nutritional deficiency, a medical condition, or simply being naturally lean. If your child is below the 5th percentile, discuss with your pediatrician to rule out any underlying issues.
Restrictive diets are generally not recommended for growing children. Instead, focus on improving the quality of food (more fruits, vegetables, whole grains), increasing physical activity, reducing screen time, and ensuring adequate sleep. For obese children, a pediatrician may recommend a specific plan.
The CDC growth charts are based on a diverse U.S. population sample but may not perfectly represent all ethnic groups. Some studies suggest different body composition patterns among various populations. The WHO growth standards (used internationally for children under 5) offer an alternative reference.