Child & Teen BMI Category Calculator (Ages 2–20)
Free Bmicalculator kids Calculator with medically-sourced formulas. Enter your measurements for personalized, accurate health insights.
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.
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\nWeight = 70 lbs = 31.75 kg\nBMI = 31.75 / (1.397)^2 = 31.75 / 1.952 = 16.3\nFor a 10-year-old boy, BMI of 16.3 falls between the 5th percentile (14.8) and 85th percentile (19.8)\nCategory: 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\nWeight = 130 lbs = 58.97 kg\nBMI = 58.97 / (1.626)^2 = 58.97 / 2.644 = 22.3\nFor a 14-year-old girl, BMI of 22.3 falls between 5th (16.2) and 85th (23.9) percentiles\nCategory: 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.
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 average cost of raising a child?
The USDA estimated $233,610 to raise a child to age 17 (2015 data, not adjusted for inflation). With current inflation, estimates exceed $300,000. Major expenses: childcare (16–18% of household expenditure), food (15–18%), housing (26–29%), transportation (12–14%), healthcare (8–9%), education/activities (2–7%). Costs vary significantly by geography and family income.
How do I calculate a child support payment?
Child support formulas vary by state/country. The US Income Shares Model (used by most states) bases support on both parents' incomes, the number of children, and custody arrangement. Basic support is determined from state guidelines tables; then divided proportionally by income. Additional expenses like childcare and medical costs are often added. Use your state's official guidelines worksheet for accurate calculations.