yrs
Enter age between 2 and 20 years.
Ages 2-20. Decimals OK (e.g. 7.5 for 7.5 years)
CDC charts are sex-specific for children
lb
Enter weight in pounds.
ft
Enter feet portion of height.
in
Enter inch portion (0-11).
BMI
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⚠️ Medical Disclaimer: This calculator is for educational purposes only. BMI is a screening tool, not a diagnostic measure. Always consult your child's pediatrician for professional assessment of growth, weight, and health status. Do not modify your child's diet without medical guidance.
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Sources & Methodology
Child BMI calculation and percentile categories verified against CDC 2000 BMI-for-age growth charts and the American Academy of Pediatrics (AAP) clinical guidelines.
CDC — Child and Teen BMI Calculator and Charts
Official CDC BMI-for-age growth charts for boys and girls ages 2-20. Percentile thresholds and weight status categories used as the basis for this calculator
AAP — Clinical Guidance on Obesity in Children
American Academy of Pediatrics evidence-based guidelines for identifying and managing overweight and obesity in children and adolescents
Methodology: BMI (metric) = weight (kg) / height (m)^2. BMI (imperial) = 703 x weight (lb) / height (inches)^2. Percentile estimated using LMS method approximation based on CDC 2000 growth chart data. CDC weight categories: below 5th percentile = underweight, 5th-84th = healthy weight, 85th-94th = overweight, 95th and above = obese. Healthy weight range derived from 5th-85th percentile BMI values for each age/sex combination.
⏱ Last reviewed: April 2026
How Child BMI Is Calculated — CDC Guide 2026
Child BMI is one of the most important pediatric health screening tools used by pediatricians worldwide. Unlike adult BMI, which uses fixed cutoff numbers, child BMI must be interpreted using age- and sex-specific percentile charts. The same BMI number means very different things at age 5 versus age 15, and for boys versus girls — this calculator accounts for both.
The Child BMI Formula
BMI = weight (kg) / height (m)^2
Imperial: BMI = 703 x weight (lb) / height (inches)^2
Example: Child weighing 70 lbs at 50 inches: BMI = 703 x 70 / (50^2) = 49,210 / 2,500 = 19.7
Example: Child weighing 70 lbs at 50 inches: BMI = 703 x 70 / (50^2) = 49,210 / 2,500 = 19.7
CDC Weight Status Categories by Percentile
| Weight Status | Percentile Range | Action |
|---|---|---|
| Underweight | Below 5th percentile | Consult pediatrician — may need nutritional evaluation |
| Healthy Weight | 5th to 84th percentile | Continue current healthy habits |
| Overweight | 85th to 94th percentile | Pediatrician visit recommended |
| Obese | 95th percentile and above | Medical evaluation recommended |
Why Child BMI Uses Percentiles Instead of Fixed Numbers
Children's body composition changes dramatically as they grow, and normal BMI values differ significantly by age and sex. A 5-year-old boy with BMI 16 is at a healthy weight, while the same BMI in a 15-year-old boy would indicate underweight. Girls typically have higher body fat percentages than boys at the same BMI, which is why the CDC maintains separate charts for each sex. The percentile system accounts for all of these normal developmental changes.
Approximate Healthy BMI Ranges by Age
| Age | Healthy BMI — Boys (5th-85th %ile) | Healthy BMI — Girls (5th-85th %ile) |
|---|---|---|
| 5 years | 13.8 – 17.0 | 13.6 – 17.0 |
| 8 years | 13.8 – 18.6 | 13.5 – 18.8 |
| 10 years | 14.4 – 20.0 | 14.3 – 20.7 |
| 12 years | 15.2 – 21.7 | 15.1 – 22.5 |
| 15 years | 17.0 – 24.0 | 16.5 – 24.5 |
| 18 years | 18.4 – 26.0 | 17.6 – 26.5 |
💡 Important for Parents: BMI is a screening tool, not a diagnosis. A child with a high BMI percentile is not automatically unhealthy — athletic children with high muscle mass may have high BMI despite low body fat. Conversely, a child in the healthy weight range may still have poor diet and fitness. Always discuss BMI results with your child's pediatrician who knows your child's complete growth history.
Frequently Asked Questions
Child BMI = weight (kg) / height (m)^2, or BMI = 703 x weight (lb) / height (inches)^2. The BMI number is then plotted on CDC age- and sex-specific percentile charts to determine weight status. The same BMI means different things at different ages and for boys vs girls.
A healthy weight for children is a BMI-for-age between the 5th and 85th percentile on CDC growth charts. Below 5th = underweight, 5th-84th = healthy weight, 85th-94th = overweight, 95th and above = obese. The actual BMI number considered healthy differs by age and sex.
BMI percentile compares a child's BMI to other children the same age and sex. A child at the 60th percentile has a BMI higher than 60% of children their age and sex. The CDC defines healthy weight as 5th-84th percentile, overweight as 85th-94th, and obese as 95th percentile and above.
Children's body composition changes as they grow, and normal body fat differs by age and sex. The CDC BMI-for-age percentile system accounts for these normal developmental changes. Using fixed adult BMI thresholds for children would be inaccurate and misleading.
For a 10-year-old boy, overweight starts at approximately BMI 19.0 (85th percentile) and obese at 21.5 (95th percentile). For a 10-year-old girl, overweight starts around BMI 19.5 (85th percentile) and obese at 22.3. These are age- and sex-specific, not fixed numbers.
BMI is a screening tool, not a diagnostic one. It correlates reasonably with body fat across populations but is imperfect for individuals. Muscular children may have high BMI despite low body fat. BMI should be interpreted alongside physical exam, diet, activity level, and family history by a pediatrician.
Consult your pediatrician if your child's BMI is at or above the 85th percentile. Do not put children on restrictive diets without medical supervision. Pediatricians typically focus on maintaining current weight while the child grows taller (naturally lowering BMI), increasing physical activity, and improving diet quality.
Child BMI (imperial) = 703 x weight (lb) / height (inches)^2. Example: 70 lbs at 50 inches: BMI = 703 x 70 / (50 x 50) = 19.7. Then use CDC growth charts to find the age- and sex-specific percentile for that BMI value.
The CDC BMI-for-age growth charts (published 2000) show BMI percentile curves from ages 2-20 for boys and girls separately. Developed from large nationally representative US samples, they allow healthcare providers to track a child's BMI relative to peers of the same age and sex.
Yes. BMI-for-age below the 5th percentile indicates underweight, which can signal inadequate nutrition or medical conditions affecting growth. Underweight children may have nutritional deficiencies, delayed puberty, or weakened immune function. A pediatrician should evaluate any child consistently below the 5th percentile.
Adult BMI categories are used for ages 20 and older. For children and adolescents ages 2-19, BMI-for-age percentile must be used. At age 20, the transition to adult BMI categories (underweight below 18.5, normal 18.5-24.9, overweight 25-29.9, obese 30+) is appropriate.
A healthy weight is the weight range corresponding to 5th-85th BMI-for-age percentile. This range shifts with age. For a 7-year-old boy, healthy BMI is roughly 13.8-17.4. By age 15, that shifts to 17.0-24.0. Always use CDC growth charts for the age-appropriate range.
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