Child & Teen BMI Category Calculator (Ages 2–20)
Free Child & Teen BMI Category Calculator (Ages 2–20) with medically-sourced formulas. Enter your measurements for personalized, accurate health insights.
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Child & Teen BMI Category Calculator (Ages 2–20)
Calculator
Adjust values & calculateEnter your values below. Every result is computed in your browser — no data is sent to any server.
Formula: BMI = Weight (kg) / Height (m)^2; then plotted on CDC age-sex growth charts
Worked example — BMI: 16.3 | Category: Healthy Weight | Percentile: 5th to 84th
Formula
BMI = Weight (kg) / Height (m)^2; then plotted on CDC age-sex growth charts
Where weight is in kilograms and height is in meters. The resulting BMI value is then compared to age-and-sex-specific CDC percentile charts to determine the weight category, since healthy BMI ranges change as children grow. The cut-offs built into this page are rounded approximations of the CDC 5th, 85th and 95th percentile values and are intended for orientation only. For a clinical reading, use the official CDC child and teen BMI calculator or the growth chart your paediatric service uses.
Worked Examples
Example 1: 10-Year-Old Boy BMI Assessment
Problem:A 10-year-old boy weighs 70 pounds and is 4 feet 7 inches tall. Calculate his BMI and determine his weight category.
Solution:Height = 4 ft 7 in = 55 inches = 1.397 meters Weight = 70 lbs = 31.75 kg BMI = 31.75 / (1.397)^2 = 31.75 / 1.952 = 16.3 For a 10-year-old boy, BMI of 16.3 falls between the 5th percentile (14.8) and 85th percentile (19.8) Category: Healthy Weight (approximately 50th percentile)
Result:BMI: 16.3 | Category: Healthy Weight | Percentile: 5th to 84th
Example 2: 14-Year-Old Girl BMI Assessment
Problem:A 14-year-old girl weighs 130 pounds and is 5 feet 4 inches tall. Calculate her BMI and weight category.
Solution:Height = 5 ft 4 in = 64 inches = 1.626 meters Weight = 130 lbs = 58.97 kg BMI = 58.97 / (1.626)^2 = 58.97 / 2.644 = 22.3 For a 14-year-old girl, BMI of 22.3 falls between 5th (16.2) and 85th (23.9) percentiles Category: Healthy Weight
Result:BMI: 22.3 | Category: Healthy Weight | Percentile: 5th to 84th
Frequently Asked Questions
Why is BMI calculated differently for children than adults?
BMI for children and teens aged 2 to 20 is interpreted differently because body composition varies significantly with age and gender during growth and development. Unlike adults who use fixed BMI ranges, children's BMI is plotted on age-and-sex-specific growth charts from the CDC to determine a percentile ranking. A child at the 60th percentile has a BMI greater than 60 percent of children of the same age and sex. This percentile approach accounts for the natural changes in body fat that occur during puberty and normal development, making it a more accurate assessment tool than using adult BMI cutoffs.
What BMI percentile ranges indicate healthy weight for children?
The CDC defines four weight categories for children based on BMI-for-age percentiles. Underweight is below the 5th percentile, meaning the child has a lower BMI than 95 percent of peers of the same age and sex. Healthy weight falls between the 5th and 84th percentiles, which is the target range for most children. Overweight is defined as the 85th to 94th percentile, indicating the child has a higher BMI than most peers. Obesity is at or above the 95th percentile. Severe obesity is sometimes classified as at or above the 120 percent of the 95th percentile BMI value.
At what age should I start tracking my child's BMI?
The CDC recommends tracking BMI-for-age beginning at age 2. Before age 2, weight-for-length measurements are used instead because BMI calculations are not reliable for infants and toddlers whose body proportions are still rapidly changing. Pediatricians typically calculate and plot BMI at annual well-child visits starting at age 2 and continuing through age 20. Regular tracking allows early identification of concerning trends in weight gain or loss. It is important to note that a single BMI measurement is less informative than tracking changes over time, as children naturally experience fluctuations during growth spurts.
Can a muscular or athletic child have a high BMI but still be healthy?
Yes, BMI has limitations because it measures weight relative to height without distinguishing between muscle mass, bone density, and body fat. A very athletic child with significant muscle mass may have a high BMI but actually have low body fat and excellent physical fitness. This is why BMI should be used as a screening tool rather than a diagnostic measure. Pediatricians consider additional factors including waist circumference, skin fold thickness measurements, diet quality, physical activity levels, family health history, and overall growth patterns before making any health assessments based on BMI percentile results alone.
What should I do if my child's BMI indicates they are overweight or obese?
If your child's BMI percentile indicates overweight or obesity, consult your pediatrician for a comprehensive evaluation. They may assess dietary habits, physical activity levels, family history, and screen for related health conditions. For most children, the goal is not weight loss but rather maintaining current weight while they grow taller, allowing BMI to naturally decrease. Focus on increasing physical activity to at least 60 minutes daily, offering more fruits, vegetables, and whole grains, reducing sugary drinks and processed foods, and limiting screen time. Avoid restrictive diets for children as they need adequate nutrition for growth and development.
What is the difference between a BMI percentile and a BMI z-score?
A percentile states the rank of a child among children of the same age and sex, so the 60th percentile means a higher value than sixty percent of that reference group. A z-score expresses the same position as a number of standard deviations from the reference median. Percentiles are easier to explain to families, but they compress at the extremes, where many different values all map close to the 99th. Clinicians therefore often prefer z-scores for tracking children far from the median.
Why does the healthy range fall and then rise across ages five to twenty?
Body fat is high in infancy, falls through early childhood as children lengthen faster than they gain mass, reaches a minimum usually somewhere in the preschool to early school years, then climbs again through later childhood and adolescence. That turning point is called the adiposity rebound. Because the underlying distribution shifts with age, a fixed adult cut-off would misclassify most children, which is why age and sex specific reference values are used instead.
How does the timing of puberty affect a percentile?
Adolescents who enter puberty early gain height, muscle and fat sooner than same-age peers, so their index can jump toward a higher percentile without any change in habits. Later maturers can drift the other way. Because the reference charts are organised by chronological age rather than by maturational stage, a single measurement taken during a growth spurt is easy to misread. Tracking the trajectory across several visits is far more informative than one point.
Which measurement errors matter most for a pediatric result?
Height dominates, because it is squared in the denominator, so a child measured with shoes on, with the heels off the floor, or with the head tilted can shift a full percentile band. Weight errors matter less but still count: heavy clothing, or weighing after a meal rather than consistently at the same point in the day. Using the same scale and stadiometer and the same routine at each visit makes the trend far more trustworthy than the absolute value.
How do the CDC growth charts differ from the WHO child growth standards?
The CDC charts are a reference: they describe how a sampled population of children actually grew. The WHO charts are a standard: they describe how children grew under favourable conditions, including recommended feeding practices, and so represent a prescriptive target. The two therefore give slightly different percentiles for the same child. Which set applies depends on the age of the child and on local clinical guidance, so follow whichever your paediatric service uses.
References
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist · Editorial policy
Related Calculators
🧮BMI Calculator - Body Mass Index
Calculate bmicalculator body mass index with inputs, formulas, and instant results.
🧮BMI Calculator for Men — Healthy Weight Ranges
Calculate bmicalculator for men with inputs, formulas, and instant results.
🧮BMI Calculator for Teens
Calculate bmicalculator for teens with inputs, formulas, and instant results.
🧮BMI Calculator for Women — Ranges by Age
Calculate bmicalculator for women with inputs, formulas, and instant results.
🧮BMI Calculator for Older Adults (Age 65+)
Calculate geriatric bmicalculator with inputs, formulas, and instant results.
🧮RFM Calculator - Relative Fat Mass
Calculate rfmcalculator relative fat mass with inputs, formulas, and instant results.
🧮How Much Weight Have You Lost? % Calculator
Calculate weight loss percentage with inputs, formulas, and instant results.
🧮Gastric Sleeve Weight Loss Calculator
Calculate gastric sleeve weight loss with inputs, formulas, and instant results.