How is BMI for kids different from BMI for adults?

For adults, BMI categories (underweight, normal, overweight, obese) are fixed numerical thresholds that apply to everyone over 18. For children ages 2 to 19, the same BMI value is interpreted differently depending on age and sex because body composition changes substantially during growth and development. A BMI of 18 is healthy for a 10-year-old boy but would be underweight for a 19-year-old. The CDC uses sex-specific BMI-for-age percentile charts to account for these changes.

What BMI percentile is healthy for a child?

According to CDC growth chart reference data, a BMI between the 5th and 85th percentile is considered healthy weight for children. Below the 5th percentile is classified as underweight. Between the 85th and 95th percentile is overweight. At or above the 95th percentile is obese. These categories apply to children ages 2 to 19 and are sex-specific because boys and girls have different growth trajectories.

How do I calculate my child's BMI?

BMI for children uses the same formula as adults: weight in kilograms divided by height in metres squared. For a child weighing 35 kg and 140 cm tall: height in metres = 1.40; BMI = 35 / (1.40 x 1.40) = 35 / 1.96 = 17.9. The difference from adult BMI is in interpretation - 17.9 needs to be compared to the CDC percentile chart for the child's age and sex to determine if it is a healthy range.

What does it mean if my child's BMI is at the 85th percentile?

A BMI at or above the 85th percentile but below the 95th percentile is classified as overweight per CDC guidelines. This means your child's BMI is higher than 85 percent of children of the same age and sex in the CDC reference population. It is a flag for closer monitoring and discussion with a pediatrician, but not necessarily an indication that a child needs to lose weight. A full assessment of growth trajectory, diet, activity level, and any health markers provides a more complete picture.

Is a high BMI percentile always a health concern for children?

Not always. A child who is very muscular or tall for their age may have a high BMI percentile without excess body fat. BMI does not directly measure body fat. A pediatrician will use BMI percentile alongside growth trajectory charts, waist circumference, blood pressure, and lab values to assess health risk. A child who is consistently at the 90th percentile across multiple measurements is generally less concerning than one who has moved rapidly from the 50th to the 90th percentile over a year.

What should I do if my child's BMI is in the obese range?

Consult your child's pediatrician before making any significant changes to their diet or activity level. The focus for children is almost always on healthy habit development rather than weight loss, especially for younger children who are still growing. Recommendations typically include reducing screen time, increasing daily physical activity (60 minutes of moderate to vigorous activity is recommended), improving diet quality (more vegetables, whole grains, and lean protein, fewer ultra-processed foods and sugary drinks), and ensuring adequate sleep.

Can children have a normal BMI percentile but still be unhealthy?

Yes. A child with a healthy BMI percentile can still have poor fitness, a nutrient-deficient diet, inadequate sleep, or other health risks not captured by BMI. BMI is a population-level screening tool. Conversely, a child with a slightly elevated percentile who is physically active, eats a varied diet, has good cardiovascular fitness, and is growing along their growth curve may be perfectly healthy. Health is not defined by a single number.

What is the healthy weight range for a 10-year-old boy?

For a 10-year-old boy at average height (138 cm), the 5th percentile BMI cutoff is approximately 14.1 and the 85th percentile cutoff is approximately 19.4. This translates to a healthy weight range of roughly 26.9 to 37.0 kg. These values differ for girls of the same age (female percentile cutoffs are slightly different) and vary with actual height. Use the Healthy Weight Range mode in this calculator for precise values based on your child's actual height.

BMI Calculator for Kids

Q: What is the CDC BMI percentile classification for children?

The CDC BMI-for-age percentile categories are: Underweight (below the 5th percentile), Healthy Weight (5th to below 85th percentile), Overweight (85th to below 95th percentile), and Obese (at or above the 95th percentile). These categories were established from NHANES reference data collected on US children across multiple survey periods and published in the CDC 2000 Growth Charts.

Q: Why do boys and girls have different BMI percentile cutoffs?

Boys and girls have different growth and body composition trajectories during childhood and adolescence. Girls typically accumulate more body fat at earlier ages, particularly during puberty, while boys tend to have a longer period of lean mass growth. The CDC growth charts are sex-specific to account for these biological differences. Using male charts for a girl or vice versa would produce inaccurate percentile classifications.

Find your child's BMI, CDC percentile category, and healthy weight range for their age and sex.

Unit System

Child's Sex

Age10

yrs

219

Weight35

10 kg100 kg

Enter height only. The healthy weight range (5th to 85th percentile) is calculated for the child's height, age, and sex.

Height140

80 cm210 cm

BMI

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CDC Cutoffs for This Age & Sex

5th Percentile (BMI)

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85th Percentile (BMI)

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95th Percentile (BMI)

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Healthy Weight Low (5th pct)

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Healthy Weight High (85th pct)

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BMI Low (5th pct)

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BMI High (85th pct)

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🧒 What is BMI for Kids?

Body Mass Index (BMI) for children is a screening measure that uses weight and height to estimate whether a child has a healthy body weight relative to their age and sex. The BMI formula is the same as for adults (weight in kg divided by height in metres squared), but for children ages 2 to 19, the result is interpreted using age- and sex-specific percentile charts rather than fixed numerical cutoffs.

The reason for this different approach is that children's bodies change substantially as they grow. A BMI of 18, for example, is solidly healthy for a 10-year-old boy but would be classified as underweight for a 19-year-old. Body fat percentage and distribution shift throughout childhood and adolescence, with girls typically developing more body fat at earlier ages and boys adding more lean mass during late adolescence. The CDC growth charts account for these sex- and age-specific differences by expressing a child's BMI as a percentile relative to same-age, same-sex peers from the CDC's reference population (the NHANES national survey database, 2000).

The four standard CDC weight-status categories for children are: Underweight (below the 5th percentile), Healthy Weight (5th to below the 85th percentile), Overweight (85th to below the 95th percentile), and Obese (at or above the 95th percentile). These percentile thresholds were chosen based on associations with health risk data showing that children above the 85th percentile have elevated risk factors for cardiovascular disease, insulin resistance, and other metabolic conditions.

BMI is a population-level screening tool and not a diagnosis. A single BMI measurement tells you where a child falls relative to the reference population on one occasion. It does not directly measure body fat, does not account for muscle mass or bone density, and is not sufficient on its own to determine whether a child has a weight-related health problem. Pediatricians use BMI percentile as one data point among many, including growth trajectory over time, physical activity level, diet quality, blood pressure, and other metabolic markers. This calculator provides accurate CDC category classification to support informed conversations with healthcare providers.

📐 Formula

BMI = W ÷ H²

W = Weight in kilograms (kg)

H = Height in metres (m) — convert cm to m by dividing by 100

CDC Categories (ages 2-19): Below 5th percentile = Underweight • 5th to 85th = Healthy • 85th to 95th = Overweight • 95th+ = Obese

Example (boy, age 10, 35 kg, 138 cm): H = 1.38 m • BMI = 35 ÷ (1.38 × 1.38) = 35 ÷ 1.904 = 18.4. For a 10-year-old boy, the 85th percentile BMI is ~19.4, so this child is in the Healthy Weight range.

📖 How to Use This Calculator

Steps

Select units and sex - choose Metric or Imperial and the child's sex. Sex is required because CDC percentile cutoffs differ between boys and girls.

Enter age, weight, and height - use the number fields or sliders. Age must be between 2 and 19 years. Measure height with shoes off, standing straight against a wall for accuracy.

Click Calculate (BMI Percentile mode) - see the child's BMI, CDC category, percentile range description, and the exact 5th, 85th, and 95th percentile BMI cutoffs for that age and sex.

Switch to Healthy Weight Range mode - click the tab to see the weight range (in kg and lbs) that keeps the child between the 5th and 85th BMI percentile for their specific height, age, and sex.

💡 Example Calculations

Example 1 - 10-Year-Old Boy, Healthy Weight

Male, age 10, 35 kg, 138 cm

Height in metres: 138 cm / 100 = 1.38 m. BMI = 35 / (1.38 x 1.38) = 35 / 1.9044 = 18.4.

For a 10-year-old boy: 5th percentile BMI = 14.1, 85th percentile = 19.4, 95th percentile = 22.1.

BMI 18.4 is above 14.1 (5th) and below 19.4 (85th), so the child is in the Healthy Weight category.

BMI = 18.4 | Category: Healthy Weight (5th to 85th percentile)

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Example 2 - 13-Year-Old Girl, Overweight

Female, age 13, 60 kg, 158 cm

Height in metres: 158 cm / 100 = 1.58 m. BMI = 60 / (1.58 x 1.58) = 60 / 2.4964 = 24.0.

For a 13-year-old girl: 5th percentile BMI = 15.8, 85th percentile = 22.6, 95th percentile = 26.2.

BMI 24.0 is above 22.6 (85th) but below 26.2 (95th), so the child is in the Overweight category.

BMI = 24.0 | Category: Overweight (85th to 95th percentile)

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Example 3 - 7-Year-Old Boy, Healthy Weight Range

Male, age 7, height 122 cm - finding the healthy weight range

For a 7-year-old boy: 5th percentile BMI = 13.2, 85th percentile = 16.8. Height in metres = 1.22.

Healthy weight low = 13.2 x (1.22 x 1.22) = 13.2 x 1.4884 = 19.6 kg.

Healthy weight high = 16.8 x (1.22 x 1.22) = 16.8 x 1.4884 = 25.0 kg.

Healthy weight range for this child: 19.6 to 25.0 kg

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❓ Frequently Asked Questions

How is BMI calculated for children?+

The BMI formula for children is identical to the adult formula: weight in kilograms divided by height in metres squared. The difference is in interpretation. For a 10-year-old girl weighing 32 kg and 138 cm tall, BMI = 32 / (1.38 x 1.38) = 16.8. This value is then compared to CDC percentile charts for 10-year-old girls to determine whether it falls into the underweight, healthy, overweight, or obese category.

What is a healthy BMI for a 10-year-old?+

For a 10-year-old boy of average height (138 cm), a BMI between approximately 14.1 and 19.4 falls in the healthy weight range (5th to 85th percentile). For a 10-year-old girl of average height, the equivalent range is approximately 13.9 to 19.7. These values vary with actual height. The calculator computes exact values for your child's specific measurements.

What BMI percentile is considered overweight for children?+

The CDC classifies a child as overweight when their BMI falls at or above the 85th percentile but below the 95th percentile for their age and sex. A child at exactly the 85th percentile has a BMI equal to or greater than 85% of same-age, same-sex children in the CDC reference population. Being in the overweight category warrants monitoring and a pediatrician consultation, but does not automatically require a weight-loss intervention.

What does a BMI at the 95th percentile mean for my child?+

At or above the 95th percentile is classified as obese per CDC guidelines. This means the child's BMI is higher than 95% of same-age, same-sex peers in the CDC reference population. A pediatrician should assess the child's overall health, diet, activity level, and medical history. Intervention typically focuses on healthy lifestyle habits rather than caloric restriction in growing children.

Why do boys and girls have different BMI percentile cutoffs?+

Boys and girls have different patterns of growth and body composition change throughout childhood and adolescence. Girls typically accumulate more body fat earlier, particularly during puberty (ages 10 to 14). Boys tend to add more lean mass during late adolescence (ages 14 to 18). The CDC growth charts are sex-specific to account for these biological differences. Using the wrong chart would give inaccurate category classifications.

Can a child have a high BMI percentile but still be healthy?+

Yes. A child who is taller than average, more muscular, or who has denser bones may have a higher BMI percentile without excess body fat. BMI does not directly measure body fat percentage or distribution. A pediatrician uses BMI percentile alongside growth trajectory over time, waist circumference, blood pressure, cholesterol, and clinical observation to get a complete picture. A one-time elevated BMI reading in a fit, active child is generally less concerning than a sustained increase over multiple measurements.

Is it safe for children to try to lose weight to lower their BMI?+

Intentional caloric restriction and weight loss programs should only be undertaken for children under direct pediatric or dietitian supervision, as calorie restriction can interfere with normal growth and development. For most children in the overweight or obese range, the goal is not weight loss but weight stabilization - allowing the child to grow into their current weight as height increases. Focus is on healthy habits: daily physical activity, whole-food diet, reduced screen time, and adequate sleep.

What is the BMI formula in imperial units for children?+

In imperial units, BMI = (weight in pounds / height in inches squared) x 703. For a child weighing 77 lbs and 55 inches tall: BMI = (77 / (55 x 55)) x 703 = (77 / 3025) x 703 = 0.02545 x 703 = 17.9. This calculator accepts imperial inputs and converts internally so you do not need to do this conversion manually.

How often should I check my child's BMI?+

Pediatricians typically measure BMI at every well-child visit (annually for most age groups). For parents monitoring at home, checking every 3 to 6 months and recording both the BMI value and the child's age provides a useful growth trajectory. Trends over time are more informative than any single measurement. A child who has moved from the 60th to the 90th percentile over 12 months warrants more attention than one who has been consistently at the 90th percentile for years.

What does 'below the 5th percentile' mean for a child?+

Below the 5th percentile is classified as underweight. This means the child's BMI is lower than 95% of same-age, same-sex peers in the CDC reference population. Underweight in children can indicate inadequate calorie or nutrient intake, underlying medical conditions, or be a normal variation for a lean, healthy child. A pediatrician should evaluate the cause. Rapid weight loss or failure to gain weight appropriate to age always warrants medical assessment.

How is this different from adult BMI categories?+

Adult BMI categories use fixed numerical thresholds that apply to all adults regardless of age or sex: underweight below 18.5, normal 18.5 to 24.9, overweight 25.0 to 29.9, and obese 30 and above. For children, the same BMI number means something entirely different at age 6 versus age 16. The percentile-based system adjusts for growth, ensuring that a BMI which is normal for a young child but high for a teenager is classified correctly for each stage of development.

🔗 Related Calculators

📌 Quick Tips

💡Children's BMI is interpreted differently from adults. The same BMI value can be healthy, overweight, or underweight depending on a child's age and sex. Always use age- and sex-specific CDC percentile categories, not the adult classification.

💡A BMI percentile between the 5th and 85th is considered healthy for children. Being above the 85th percentile does not automatically mean a child needs to diet - consult a pediatrician for a full assessment that includes growth trajectory, activity level, and diet.

💡BMI for children is a screening tool, not a diagnosis. A child with high muscle mass from sport may show an elevated BMI percentile without excess body fat. A pediatrician combines BMI with other measurements and observations.

💡Children's BMI naturally changes as they grow. A child who is in a higher percentile category at age 8 may move into a healthier range by age 12 as height catches up to weight. Track trends over time rather than reacting to a single measurement.

💡Healthy habits matter more than a specific number on the scale. Regular physical activity (at least 60 minutes per day for children), a balanced diet rich in vegetables and whole grains, and adequate sleep are the core building blocks of healthy child development.