BMI Calculator for Children & Teens
Calculate BMI for children and teens ages 2-20 using CDC growth chart percentiles. BMI in children is age and gender-specific.
CDC Weight Categories for Children
Underweight (< 5th percentile)
Below healthy range — consult a pediatrician
Healthy Weight (5th – 84th percentile)
Normal, age-appropriate weight
Overweight (85th – 94th percentile)
Above healthy range for age and sex
Obese (≥ 95th percentile)
Well above healthy range — seek medical guidance
Understanding BMI in Children: A Parent's Complete Guide
Body Mass Index for children and teens is fundamentally different from adult BMI. While adult BMI uses fixed categories (underweight < 18.5, normal 18.5-24.9), children's BMI must be interpreted using age- and sex-specific growth charts because body composition changes dramatically during development. A BMI of 18 is perfectly healthy for a 10-year-old boy but may indicate underweight for a 16-year-old. The CDC growth charts used in this calculator are based on national health surveys of thousands of American children from the 1960s through the 1990s.
According to the CDC, approximately 19.7% of U.S. children and adolescents ages 2-19 are obese (at or above the 95th percentile), and an additional 16.1% are overweight (85th to 94th percentile). Childhood obesity rates have tripled since the 1970s, making this screening tool more important than ever. However, BMI is a screening tool, not a diagnostic measure — always consult a pediatrician for a comprehensive assessment. For adults, use our standard BMI calculator.
How CDC Growth Charts Work
The CDC BMI-for-age growth charts compare a child's BMI to reference populations of children of the same age and sex. Percentiles indicate how a child's BMI compares to others. A child at the 75th percentile has a higher BMI than 75% of children their age and sex. The four weight status categories are:
Underweight (< 5th percentile)
May indicate nutritional deficiency, growth delay, or underlying medical condition. The pediatrician will evaluate growth trajectory, dietary intake, and rule out conditions like celiac disease or thyroid disorders.
Healthy Weight (5th–84th percentile)
Appropriate weight for age and height. This broad range accounts for the natural diversity in children's body types. Focus on maintaining healthy eating habits and regular physical activity (60 minutes daily per WHO guidelines).
Overweight (85th–94th percentile)
Above the recommended range. Small lifestyle changes can be effective: reducing screen time, increasing outdoor play, and improving dietary quality. Avoid restrictive dieting — growing children need adequate nutrition.
Obese (≥ 95th percentile)
Significantly above the healthy range. Associated with increased risk of type 2 diabetes, high blood pressure, and psychological effects. Professional guidance from a pediatrician or pediatric nutritionist is recommended.
Important: The goal for overweight children is usually to slow weight gain so they "grow into" their weight, rather than weight loss. Growing children need sufficient calories and nutrients for development. For adults tracking their own health alongside their children's, use our body fat calculator or ideal weight calculator.
BMI Changes During Normal Development
Children's BMI follows a characteristic pattern called the "adiposity rebound." BMI increases during infancy, then decreases through early childhood (ages 2-5), reaching its lowest point around age 5-6. It then rises through adolescence into adulthood. Children who experience an early adiposity rebound (before age 5) are at higher risk for overweight in later years. This is why tracking BMI trends over time — not just single measurements — is crucial.
Puberty causes significant changes: boys typically gain muscle mass (which increases BMI without excess fat), while girls naturally increase body fat percentage. These developmental changes make the age- and sex-specific percentile approach essential. Your pediatrician will plot your child's BMI on growth charts at each well-child visit to monitor trends. For tracking calorie and nutrition needs during growth, consider using our calorie calculator and protein calculator.
Healthy Habits for Children at Any BMI
- 60 minutes of physical activity daily: The WHO recommends at least 60 minutes of moderate-to-vigorous activity for children aged 5-17. This can include sports, active play, cycling, or swimming. Use our calories burned calculator to see how different activities compare.
- Limit screen time: The American Academy of Pediatrics recommends no more than 1-2 hours of recreational screen time per day for children over 6. Increased screen time is strongly correlated with childhood obesity.
- Family meals matter: Studies show children who eat regular family meals consume more fruits, vegetables, and whole grains, and have lower rates of overweight. Aim for at least 3-4 family dinners per week.
- Adequate sleep: The National Sleep Foundation recommends 9-12 hours for school-aged children (6-13) and 8-10 hours for teens. Poor sleep is linked to increased appetite hormones and weight gain. Adults can use our sleep calculator to optimize their own schedules.
- Avoid using food as reward: Associating food with emotions can lead to unhealthy eating patterns. Praise effort and behavior instead.
Remember that children's health encompasses far more than BMI alone. Physical fitness, mental health, sleep quality, and dietary diversity all contribute to wellbeing. If you're managing a family budget while prioritizing nutrition, tools like salary planning and financial calculators can help with household budgeting.
Frequently Asked Questions
Can a muscular child have a falsely high BMI?▼
Should I put my overweight child on a diet?▼
How often should children's BMI be checked?▼
Are the CDC and WHO growth charts different?▼
Health Disclaimer
This calculator is for informational and educational purposes only. Results are estimates based on general formulas and may not apply to your individual situation. This tool does not provide medical advice. Always consult a qualified healthcare professional before making health, fitness, or dietary decisions. Individual results may vary based on factors not captured by these calculations.
Frequently Asked Questions
Can a muscular child have a falsely high BMI?
Yes, but this is less common in children than adults. Athletic children who participate heavily in sports like gymnastics, swimming, or wrestling may have higher BMI due to muscle mass. A pediatrician can differentiate between excess fat and lean mass using additional assessments like skinfold measurements, waist circumference, or body composition analysis. If a child is active and eating well, an elevated BMI may not be concerning.
Should I put my overweight child on a diet?
Generally, restrictive diets are not recommended for growing children. Instead, focus on improving food quality (more fruits, vegetables, whole grains, and lean protein), increasing physical activity, and reducing sugary drinks and processed snacks. For most overweight children, the goal is weight maintenance — allowing them to "grow into" their weight as they get taller. Calorie restriction should only be undertaken with medical supervision for severely obese children.
How often should children's BMI be checked?
The American Academy of Pediatrics recommends annual BMI screening at well-child visits starting at age 2. For children with BMI above the 85th percentile, more frequent monitoring (every 3-6 months) may be appropriate. Track trends rather than single measurements — a gradual upward crossing of percentile lines is more concerning than a stable BMI at a slightly higher percentile.
Are the CDC and WHO growth charts different?
Yes. The WHO growth charts (used for children under 2 worldwide) describe how children should grow under optimal conditions (breastfed, healthy environments). The CDC growth charts (used in the U.S. for ages 2-20) describe how American children actually grew, based on national survey data. The WHO charts generally produce higher obesity rates because they use a healthier reference population. This calculator uses CDC charts, which are standard practice in the United States.