BMI Calculator for Kids & Teens (Ages 2-19 Years)
Calculate Body Mass Index (BMI) percentile for children and teenagers ages 2-19 years using CDC growth charts. This pediatric BMI calculator helps parents, caregivers, and healthcare providers assess whether a child's weight is within a healthy range for their age, sex, and height. BMI percentiles are more accurate than BMI alone for children because kids' body composition changes as they grow and develop.
⚠️ Important Medical Disclaimer: This BMI calculator is a screening tool only and not a diagnostic instrument. BMI doesn't measure body fat directly and may not accurately reflect health status in all children, especially athletes or those with high muscle mass. Always consult with a pediatrician or qualified healthcare provider for personalized medical advice, diagnosis, and treatment recommendations. This tool does not replace professional medical evaluation.
Child & Teen BMI Calculator
Quick Age Examples:
BMI Results for Your Child
Understanding BMI in Children and Teens
Body Mass Index (BMI) is a screening tool that uses height and weight to estimate body fat and assess weight status. For children and teenagers ages 2-19, BMI alone isn't enough—it must be plotted on CDC growth charts that account for age and biological sex to determine a BMI percentile. This percentile shows how a child's BMI compares to other children of the same age and sex from a representative national sample.
Unlike adults, children's bodies constantly change as they grow and develop. Body composition varies significantly with age—toddlers have different body fat ratios than teenagers. Boys and girls also develop differently, especially during puberty. These factors make age- and sex-specific BMI percentiles essential for accurate assessment of child weight status.
Why BMI Percentiles Matter for Children
BMI percentiles place a child's BMI within the context of other children their same age and sex. According to CDC data from 2017-2020, approximately 19.7% of US children and adolescents ages 2-19 are affected by obesity, representing about 14.7 million children. BMI percentiles help identify children who may be at risk for weight-related health problems and guide appropriate interventions.
BMI Calculation Formulas
Basic BMI Formula
The fundamental BMI calculation:
Or using imperial units:
Where:
- Weight = Body weight in kilograms or pounds
- Height = Height in meters or inches
- 703 = Conversion factor for imperial units
BMI Percentile Calculation (LMS Method)
CDC uses the LMS method to calculate percentiles:
Where:
- \( L \) = Power in Box-Cox transformation (skewness parameter)
- \( M \) = Median BMI value for specific age and sex
- \( S \) = Generalized coefficient of variation
- \( Z \) = Z-score (standard deviations from median)
- Percentile = Standard normal cumulative distribution of Z
L, M, and S values are age- and sex-specific from CDC growth charts
Example Calculation
Example: 10-year-old boy, 4 feet 6 inches (54 inches), 80 pounds
This BMI of 19.3 is then compared to CDC growth charts for 10-year-old boys to determine the percentile (approximately 75th percentile = healthy weight).
BMI Percentile Categories for Children
CDC classifies children's weight status into four categories based on BMI-for-age percentiles. These categories help identify children who may need additional health screening or interventions.
| BMI Percentile Range | Weight Category | Health Implications |
|---|---|---|
| Less than 5th percentile | Underweight | May indicate inadequate nutrition, growth issues, or health conditions |
| 5th to 84th percentile | Healthy Weight | Appropriate weight for height, age, and sex |
| 85th to 94th percentile | Overweight | Increased risk for weight-related health problems |
| 95th percentile or above | Obesity | High risk for serious health complications including Type 2 diabetes, cardiovascular disease |
Understanding the Range: The healthy weight range (5th-84th percentile) is intentionally broad because children's bodies vary naturally. A child at the 20th percentile can be just as healthy as a child at the 75th percentile, provided they're growing consistently along their individual growth curve and maintaining healthy habits.
Severe Obesity Classification
Children with BMI at or above 120% of the 95th percentile are classified as having severe obesity. This category faces significantly elevated risk for:
- Type 2 Diabetes: Children with obesity have 3.7 times higher likelihood of developing diabetes
- Cardiovascular Disease: High blood pressure, high cholesterol, atherosclerosis
- Nonalcoholic Fatty Liver Disease (NAFLD): Liver damage from excess fat accumulation
- Sleep Apnea: Interrupted breathing during sleep affecting growth and development
- Joint Problems: Increased stress on developing bones and joints
- Psychosocial Issues: Depression, anxiety, low self-esteem, bullying
Health Implications of Childhood Obesity
Childhood obesity represents one of the most serious public health challenges of the 21st century. Between 2017-2020, 19.7% of US children ages 2-19 were affected by obesity, representing 14.7 million children—essentially 1 in 5 children. This rate has increased by 4.6% since 1999-2000, demonstrating the urgency of addressing this epidemic.
Immediate Health Risks
Children with obesity face numerous health complications during childhood itself, not just in adulthood:
- Type 2 Diabetes: As of 2019, 39,000 children under age 20 in the US had Type 2 diabetes, with 33,150 (85%) being overweight or obese
- Prediabetes: Elevated blood glucose levels increasing diabetes risk
- High Blood Pressure: Cardiovascular strain during critical development periods
- High Cholesterol: Early atherosclerotic changes in blood vessels
- Asthma: Increased prevalence and severity in children with obesity
- Sleep Disorders: Obstructive sleep apnea affecting growth hormone release
- Bone and Joint Problems: Increased fractures, early arthritis, orthopedic complications
- Fatty Liver Disease: Liver inflammation and damage requiring screening in children 10+
Long-Term Health Consequences
Children with obesity are significantly more likely to remain obese as adults, carrying forward increased risk for chronic diseases throughout life:
- Cardiovascular Disease: Heart attack, stroke, hypertension, heart failure
- Cancer: Increased risk for 13+ cancer types including breast, colon, kidney
- Metabolic Syndrome: Cluster of conditions dramatically raising disease risk
- Osteoarthritis: Premature joint degeneration and disability
- Reproductive Issues: Polycystic ovary syndrome, infertility
Psychosocial Impact
Beyond physical health, childhood obesity significantly affects mental health and social development:
- Depression and Anxiety: Higher rates of mental health disorders
- Low Self-Esteem: Negative body image and reduced confidence
- Bullying and Social Isolation: Peer victimization and exclusion
- Academic Challenges: Lower school performance and increased absences
- Eating Disorders: Increased risk for binge eating disorder, emotional eating
⚠️ Critical Consideration: While addressing childhood obesity is important, weight-focused interventions can inadvertently increase eating disorder risk. The American Academy of Pediatrics' 2023 guidelines recommending early intensive treatment including medications (age 12+) and surgery (age 13+) have drawn criticism for not adequately addressing eating disorder prevention. Focus should be on health behaviors—nutrition, physical activity, sleep, stress management—rather than weight alone.
Factors Affecting BMI in Children
Genetics and Family History
Genetic factors influence body composition, metabolism, and appetite regulation. Children with one parent with obesity have 50% increased risk; with two parents, risk increases to 80%. However, genetics interact with environment—genes load the gun, but environment pulls the trigger.
Nutrition and Eating Patterns
- Calorie-Dense Foods: Excessive consumption of processed foods, sugary drinks, fast food
- Portion Sizes: "Super-sized" meals exceeding energy needs
- Eating Behaviors: Emotional eating, eating when not hungry, restrictive dieting (increases risk)
- Family Meal Patterns: Irregular meals, eating while screen viewing
- Food Security: Limited access to affordable, nutritious food increases obesity risk
Physical Activity Levels
Screen time dramatically impacts obesity risk. Studies show obesity rates are 8.3 times greater for children watching TV 5+ hours daily versus 2 or fewer hours. Current recommendations:
- Ages 2-5: At least 3 hours of varied physical activity daily
- Ages 6-17: At least 60 minutes of moderate-to-vigorous activity daily
- Screen Time Limits: No screens for children under 2; maximum 1-2 hours daily for older children
- Active Play: Unstructured outdoor play encouraging movement and exploration
Sleep Duration
Insufficient sleep disrupts hormones regulating hunger and satiety (ghrelin and leptin), increases appetite, and reduces physical activity due to fatigue. Recommended sleep:
- Ages 3-5: 10-13 hours per 24 hours
- Ages 6-12: 9-12 hours per night
- Ages 13-18: 8-10 hours per night
Socioeconomic and Environmental Factors
- Income Level: Lower-income families face higher obesity rates due to food costs, neighborhood safety
- Food Deserts: Limited access to supermarkets with fresh produce
- Built Environment: Lack of sidewalks, parks, safe play spaces limits physical activity
- Parental Work Schedules: Multiple jobs reducing time for meal preparation, family meals
- Marketing Exposure: Targeting of unhealthy food advertising to children
Healthy Lifestyle Strategies for Children
Nutrition Guidelines
Focus on nourishing bodies rather than restricting or dieting, which increases eating disorder risk:
- Balanced Meals: Include vegetables, fruits, whole grains, lean proteins, healthy fats
- Portion Awareness: Age-appropriate serving sizes without rigid restriction
- Family Meals: Eat together 5-6 times weekly to improve nutrition and connection
- Limit Sugary Drinks: Water and milk as primary beverages; juice limited to 4-6 oz daily
- Involve Children: Age-appropriate meal planning, grocery shopping, cooking
- Positive Food Environment: No "good" or "bad" foods; all foods fit in moderation
- Intuitive Eating Principles: Honor hunger and fullness cues; eat mindfully without distractions
✓ Evidence-Based Approach: The most effective interventions include minimum 26 hours of face-to-face, family-based, multicomponent treatment over 3-12 months, incorporating nutrition education, physical activity support, and behavior change strategies. However, access to such programs remains limited. Focus on sustainable family lifestyle changes rather than child-focused "dieting."
Physical Activity Recommendations
- Make it Fun: Choose activities children enjoy—dance, sports, playground, swimming
- Family Activity: Walk, bike, play together as a family
- Reduce Sedentary Time: Break up sitting every 30-60 minutes; active transportation
- Variety: Mix aerobic (running, biking), strength (climbing, gymnastics), and flexibility activities
- School Support: Advocate for quality physical education and recess time
- Extracurricular Options: Sports teams, dance classes, martial arts, hiking clubs
Sleep Hygiene
- Consistent Schedule: Same bedtime and wake time, including weekends
- Bedroom Environment: Cool, dark, quiet; remove screens from bedroom
- Wind-Down Routine: 30-60 minutes of calming activities before bed
- Screen Curfew: No screens 1-2 hours before bedtime (blue light disrupts melatonin)
- Physical Activity: Regular exercise improves sleep quality (but not right before bed)
Behavioral and Emotional Support
- Positive Reinforcement: Praise healthy behaviors, not weight or appearance
- Body Positivity: Model healthy body image; avoid negative weight talk
- Stress Management: Teach coping skills beyond eating; mindfulness, journaling, talking
- Professional Support: Consult pediatrician, registered dietitian, therapist if concerned
- Address Bullying: School and community interventions to prevent weight-based teasing
When to Consult a Healthcare Provider
Seek medical evaluation if your child:
- BMI above 85th percentile: Screening for comorbidities and lifestyle counseling
- BMI above 95th percentile: Comprehensive evaluation and structured intervention
- Rapid Weight Gain: Crossing two or more percentile curves upward
- Weight Loss Concerns: BMI below 5th percentile or significant weight loss
- Health Symptoms: Excessive thirst/urination (diabetes), snoring (sleep apnea), joint pain
- Family History: Strong family history of obesity, diabetes, heart disease
- Emotional Distress: Depression, anxiety, disordered eating patterns, body image issues
Screening Recommendations for Children with Elevated BMI: The AAP recommends screening children 10+ years old with BMI ≥85th percentile for Type 2 diabetes, high cholesterol, and fatty liver disease. Earlier screening may be appropriate with additional risk factors like family history, high-risk ethnicity (African American, Hispanic, Native American, Asian American, Pacific Islander), or signs of insulin resistance.
Official Government Health Resources
Access authoritative information and tools from official US government health agencies and medical organizations.
Federal Health Agencies
CDC Child & Teen BMI Calculator CDC Growth Chart Training NIH We Can! Program - Childhood Obesity Prevention Physical Activity Guidelines for AmericansMedical Organizations & Resources
WHO Growth Reference Data (5-19 years) American Academy of Pediatrics - Obesity Resources HealthyChildren.org - AAP Parent Resource MyPlate - USDA Nutrition GuidanceFrequently Asked Questions
A healthy BMI percentile for children is between the 5th and 84th percentile. This wide range reflects normal variation in body composition among healthy children. What matters most is that your child is growing consistently along their own growth curve and maintaining healthy lifestyle habits. A child at the 15th percentile can be just as healthy as one at the 75th percentile. Your pediatrician tracks BMI percentile over time to identify concerning upward or downward trends rather than focusing on a single measurement.
BMI-for-age percentiles are generally accurate screening tools for most children, correctly identifying about 85-90% of children with excess body fat. However, BMI doesn't directly measure body fat and can be inaccurate for children who are very muscular (may appear overweight/obese), going through rapid growth spurts, or have certain body types. BMI also doesn't distinguish between fat, muscle, and bone mass. For this reason, pediatricians use BMI as one piece of assessment alongside physical examination, growth pattern tracking, family history, and overall health evaluation rather than relying on BMI alone for diagnosis.
No—traditional "dieting" or calorie restriction is not recommended for children and can be harmful, increasing risk for eating disorders, growth stunting, nutrient deficiencies, and psychological distress. Instead, focus on family-based healthy lifestyle changes: nutritious meals together, regular physical activity, adequate sleep, and positive body image. Gradual behavior changes are more sustainable and healthier than weight-focused approaches. The goal for most children is weight maintenance while growing taller (reducing BMI percentile naturally) rather than weight loss. Always consult your pediatrician before making significant dietary changes. Evidence-based treatment includes structured, family-involved programs with professional support.
BMI can overestimate body fat in children with high muscle mass, particularly young athletes involved in sports requiring strength and power (football, wrestling, gymnastics, weightlifting). Muscle weighs more than fat, so muscular children may have higher BMI percentiles despite having healthy or even low body fat. Your pediatrician can assess whether the elevated BMI reflects muscle versus excess fat through physical examination, body composition measurement if needed, and evaluation of overall health. An athletic child with BMI in the overweight range who is active, eats nutritiously, has normal blood pressure and lab results, and is thriving shouldn't be a concern.
The AAP recommends BMI screening annually starting at age 2 during routine well-child visits. Regular BMI tracking creates a growth curve showing patterns over time, which is more informative than any single measurement. Children with BMI above the 85th percentile may need more frequent monitoring (every 3-6 months) along with health screening and lifestyle counseling. Children with special health conditions, eating disorders, or growth concerns may require individualized monitoring schedules. Home measurement and calculation can help track between visits, but medical-grade equipment and professional interpretation at pediatric appointments remain the gold standard.
Childhood obesity results from complex interactions between multiple factors, not a single cause. Contributors include: genetics (30-40% of obesity risk is heritable); nutrition (excessive calorie intake from processed foods, sugary drinks, large portions); physical inactivity (increased screen time, reduced outdoor play, sedentary transportation); insufficient sleep (disrupts hunger hormones); socioeconomic factors (food insecurity, limited access to healthy foods and safe activity spaces, parental work schedules); stress and trauma; medications; and rarely, underlying medical conditions or genetic syndromes. Environmental factors have changed dramatically—today's obesogenic environment promotes overconsumption and underactivity. Effective solutions require addressing multiple levels: individual, family, community, and policy.
Yes, with appropriate family-based lifestyle interventions, many children can achieve healthier weights. However, the goal isn't always weight loss—for growing children, maintaining current weight while growing taller effectively reduces BMI percentile. The most effective interventions are family-based (whole family participates), multicomponent (address nutrition, activity, behavior, emotions), intensive (minimum 26 hours over 3-12 months), and professionally supported. Success focuses on sustainable behavior changes rather than rapid weight loss: establishing regular family meals, increasing activity, reducing screen time, improving sleep. Avoid focusing on weight itself, which can harm self-esteem and increase eating disorder risk. Emphasize health, energy, strength, and wellbeing instead.
Children with BMI at or above the 85th percentile should be screened for weight-related health complications. The AAP recommends for children 10+ years old: fasting lipid panel (cholesterol), fasting glucose or HbA1c (diabetes screening), ALT and AST liver enzymes (fatty liver disease), blood pressure measurement. Additional screening may include: sleep evaluation (sleep apnea), joint examination, psychosocial assessment (depression, anxiety, self-esteem), and nutritional assessment. Younger children (under 10) or those with additional risk factors (family history of early heart disease or diabetes, high-risk ethnicity, signs of insulin resistance like acanthosis nigricans) may need earlier or additional screening. Your pediatrician will recommend appropriate testing based on individual risk factors.