Child BMI Calculator
Calculate your child's BMI-for-age percentile using CDC growth charts (ages 2–19). Get weight-status category, healthy BMI range, growth insights, pediatric guidance, and PDF export in metric or imperial units.
Enter your details — results appear below after you calculate.
Child measurements
Ages 2–19 years — CDC BMI-for-age charts
0–11 months (optional precision)
How this Child BMI calculator works
Enter your child's sex (boy or girl), age (2–19 years, with optional months), and height and weight in metric (cm, kg) or imperial (feet/inches, lb). We compute BMI and map it to the CDC BMI-for-age percentile using official growth-chart reference data—then classify weight status (underweight, healthy, overweight, or obesity).
Your report includes percentile position on the growth scale, healthy BMI and weight bands (5th–85th percentile), reference values at key percentiles, screening insights, health considerations, and family-based wellness or weight-management tips. Export a PDF or share results for pediatrician visits.
Child BMI is a screening tool—growth trends over time matter more than one reading. For adults 18+, use our Body Mass Index (BMI) Calculator. For family nutrition planning, try our Calorie, Water Intake, and Ideal Body Weight calculators.
Child BMI Calculator – CDC BMI-for-Age Percentiles & Growth Charts
Child BMI (BMI-for-age) is how pediatricians screen whether a child's weight is appropriate for their height, age, and sex. Unlike adult BMI—which uses fixed cutoffs like 18.5 and 25—children are classified by percentiles on CDC growth charts. Our Child BMI Calculator computes BMI in metric or imperial units, maps your child to the CDC percentile, shows weight-status category, healthy BMI and weight bands, and explains growth-tracking guidance so parents and caregivers can use results wisely at pediatric visits.
What Is BMI-for-Age?
The Centers for Disease Control and Prevention (CDC) publishes BMI-for-age growth charts for children and adolescents ages 2–19. Because children grow at different rates through childhood and puberty, a BMI of 17 might be healthy for a 7-year-old but underweight for a 16-year-old. Percentiles solve this by comparing each child to a reference population of the same age and sex.
1What You Enter
Required measurements
- Unit system: metric (cm, kg) or imperial (ft/in, lb)
- Sex: boy or girl (required for percentile charts)
- Age: 2–19 years, with optional additional months (0–11)
- Height (standing, without shoes)
- Current body weight (light clothing)
Best practices
- Measure at the same time of day when tracking trends
- Use a flat surface and proper stadiometer when possible
- Record results at well-child visits for official charting
2Formulas We Use
Metric BMI
BMI = weight (kg) ÷ [height (m)]²
Imperial BMI
BMI = 703 × weight (lb) ÷ [height (in)]²
BMI-for-age percentile (CDC LMS method)
We use CDC 2000 Growth Chart LMS parameters (Lambda, Mu, Sigma) to convert BMI to a sex- and age-specific percentile. Categories follow CDC definitions: underweight (<5th), healthy (5th–84th), overweight (85th–94th), obesity (≥95th).
Healthy weight band
We show BMI and weight values at the 5th, 50th, 85th, and 95th percentiles for your child's age and sex—the same reference points used on official CDC growth charts.
3CDC Weight-Status Categories
| Percentile range | Weight status |
|---|---|
| Below 5th percentile | Underweight |
| 5th to below 85th percentile | Healthy weight |
| 85th to below 95th percentile | Overweight |
| 95th percentile or above | Obesity |
4How to Read Your Results
Percentile tells you what percentage of children of the same age and sex have a lower BMI. A 70th percentile means your child's BMI is higher than 70% of the reference group—within the healthy range.
Category summarizes screening risk using CDC cutoffs. A healthy percentile does not guarantee perfect health; an elevated percentile does not mean your child is unhealthy—it signals a conversation with your pediatrician about growth trends and habits.
Growth over time is the gold standard. Plot BMI at each well-child visit. Crossing percentile lines rapidly—especially upward—may warrant clinical attention.
Common Mistakes to Avoid
1. Using adult BMI cutoffs for children
A BMI of 22 is normal for many adults but may be overweight for a young child. Always use age- and sex-specific percentiles—not adult WHO categories.
2. Panicking over a single reading
Growth is dynamic. One percentile snapshot is less informative than the trend across multiple visits. Discuss sustained changes with your pediatrician.
3. Putting children on restrictive diets
Calorie restriction without medical supervision can harm growth and development. Family-based lifestyle changes are the standard approach.
4. Ignoring muscle and activity level
Athletic children may have higher BMI without excess fat. Clinical context, activity, and growth history matter alongside percentile.
The Science Behind Child BMI
CDC BMI-for-age charts were developed from nationally representative U.S. survey data (NHANES) and released in 2000. They remain the standard for pediatric weight screening in the United States. The LMS method (Lambda-Mu-Sigma) by Tim Cole and Patrick Green smooths reference curves so percentiles can be calculated at any age-month. The American Academy of Pediatrics recommends plotting BMI at every well-child visit starting at age 2.
Related Tools on This Site
For parents and caregivers, pair child BMI with our Adult BMI Calculator (ages 18+), Ideal Body Weight Calculator, Calorie Calculator, and Water Intake Calculator for family wellness planning.
Frequently Asked Questions (FAQs)
Related Calculators
You might also be interested in these related health and wellness calculators:
Calorie Calculator
Estimate your daily calorie needs based on your age, gender, weight, height, and activity level to support weight loss, maintenance, or muscle gain goals.
Body Fat Percentage Calculator
Calculate your body fat to understand your fitness level and monitor changes over time more accurately than just weighing yourself.
Daily Water Intake Calculator
Calculate your ideal daily water intake based on your weight, activity level, climate, and lifestyle. Get personalized hydration tips to stay healthy, improve energy, and support overall well-being.
Body Mass Index (BMI) Calculator
Calculate your Body Mass Index (BMI) from height and weight in metric or imperial units. Get WHO categories, healthy weight range, BMI Prime, and PDF export.
Ideal Body Weight Calculator
Calculate ideal weight for your height using Devine, Robinson, Miller, and Hamwi formulas. See average, ideal weight range, frame-size adjustment, and current-weight comparison.
Waist-to-Height Ratio (WHtR) Calculator
Calculate waist-to-height ratio (WHtR) from waist and height. Half-height rule, target waist at 0.5, central fat risk bands—often a stronger screen than BMI alone.
Protein Target Calculator
Calculate daily protein targets in grams from body weight, goal, and training—with GLP-1 muscle-preservation (1.6–2.2 g/kg), adjusted weight above 100 kg, sedentary 0.8–1.2 g/kg, and per-meal splits.
Healthy Weight Gain & Muscle Building Calculator
Calculate your daily calorie surplus and target for healthy weight gain from body stats, activity, goal weight, goal type, and timeline. See TDEE, macro split, weekly gain rate, goal date, and safety warnings.