Updated February 2026 • 14 min read

Pediatric BMI Calculator: BMI Charts for Kids & Teens by Age

BMI for children works differently than it does for adults. Instead of using fixed cutoffs like 18.5 and 25, pediatric BMI compares your child to other children of the same age and sex using percentile charts. This guide explains how pediatric BMI is calculated, what the percentiles mean, and when parents should be concerned about their child’s weight.

Why Is Pediatric BMI Different from Adult BMI?

Adult BMI interpretation is straightforward: under 18.5 is underweight, 18.5–24.9 is normal, 25+ is overweight, and 30+ is obese. These fixed cutoffs work for adults because adult body composition is relatively stable. Children, however, are constantly growing and developing, and their body fat percentage changes dramatically with age.

A typical 5-year-old has a BMI around 15.5, which would be classified as severely underweight by adult standards. A 17-year-old athlete with a BMI of 24 would be normal by adult standards but might be at the 90th percentile for her age, technically overweight. This is why pediatric BMI requires age- and sex-specific percentile charts rather than fixed numbers.

The Centers for Disease Control and Prevention (CDC) maintains growth charts based on data from thousands of American children, and the World Health Organization (WHO) publishes international growth standards. In the United States, CDC charts are used for children ages 2–19, while WHO charts are recommended for children under 2.

Pediatric BMI Weight Categories

Instead of the adult BMI categories, children and teens are classified based on where their BMI falls on the age-sex percentile chart:

Note that the term “obese” in pediatric medicine is a clinical classification, not a judgment. It simply means the child’s BMI exceeds the 95th percentile for their age and sex, which is associated with higher health risks that merit evaluation by a healthcare provider. For more on adult BMI categories and how they differ, see our guide on BMI categories.

How to Calculate BMI for Children

The BMI formula for children is identical to the adult formula. The only difference is what you do with the result afterward.

Step 1: Measure Height and Weight Accurately

For children, accurate measurement is critical because small errors have a larger proportional impact than in adults:

• Weight: Use a calibrated digital scale. The child should wear light indoor clothing and no shoes. For infants, use an infant scale.
• Height (ages 2+): Use a stadiometer or measure against a wall. The child should stand barefoot, heels together, back and head touching the wall, looking straight ahead. Place a flat object (ruler or book) on top of the head perpendicular to the wall and mark the wall.
• Length (under age 2): For infants and toddlers, length is measured lying down (recumbent length) rather than standing height. This typically produces a value about 0.7 cm longer than standing height.

Step 2: Calculate BMI Using the Formula

Step 3: Worked Example

Let us calculate BMI for a 10-year-old boy who weighs 32 kg and is 1.38 m (138 cm) tall:

Step 4: Plot on the Growth Chart

A BMI of 16.8 for a 10-year-old boy falls at approximately the 55th percentile on the CDC growth chart. This means he weighs more than about 55% of 10-year-old boys, placing him squarely in the healthy weight category (5th–84th percentile).

If the same BMI of 16.8 belonged to a 10-year-old girl, it would be at approximately the 60th percentile — still healthy, but a different percentile because boys and girls have different growth patterns. This is why sex-specific charts are essential.

For details on the underlying math, see our BMI Formula guide.

BMI Percentile Charts for Boys (Ages 2–19)

The following table shows key BMI percentile values for boys at various ages. These values are derived from CDC growth chart data:

Notice the U-shaped pattern: BMI drops from age 2 to around age 6, then rises steadily through adolescence. The dip around age 5–6 is called the “adiposity rebound” and is a normal developmental milestone. For more age-specific BMI information, see our BMI by age guide.

BMI Percentile Charts for Girls (Ages 2–19)

Girls show a similar pattern to boys, with BMI dipping in early childhood before rising through puberty. However, girls generally have slightly higher BMI values at the upper percentiles during and after puberty, reflecting the normal increase in body fat associated with female development.

The Adiposity Rebound: A Critical Growth Milestone

One of the most important concepts in pediatric BMI is the adiposity rebound. Here is what happens:

• Birth to age 1: BMI increases rapidly (babies are naturally chubby)
• Age 1 to age 5–6: BMI gradually decreases as children grow taller relative to their weight
• Age 5–6: BMI reaches its lowest point — this is the adiposity rebound
• Age 6 to adulthood: BMI rises steadily as children gain weight relative to height

Research has consistently shown that children who experience an early adiposity rebound (before age 5) are at significantly higher risk of becoming overweight or obese later in childhood and into adulthood. If your child’s BMI starts rising before age 5, discuss this pattern with your pediatrician. It does not necessarily indicate a problem, but it warrants monitoring. The American Academy of Pediatrics (AAP) recommends regular BMI screening starting at age 2.

Understanding BMI Percentiles in Detail

Percentiles are one of the most misunderstood aspects of pediatric BMI. Here is what they actually mean:

What a Percentile Tells You

A BMI percentile indicates what percentage of children of the same age and sex have a lower BMI. For example:

• 25th percentile: Your child’s BMI is higher than 25% of same-age, same-sex peers (and lower than 75%)
• 50th percentile: Your child’s BMI is right at the middle — higher than half, lower than half
• 85th percentile: Your child’s BMI is higher than 85% of peers — the overweight threshold

What a Percentile Does NOT Tell You

• It does not measure body fat directly (muscular children can have high percentiles)
• It does not indicate fitness level or physical activity
• It does not account for growth timing (early vs. late bloomers)
• A higher percentile is not inherently “worse” than a lower one within the healthy range

Tracking Percentile Trends

More important than any single percentile reading is the trajectory over time. A child who has consistently been at the 70th percentile is in a very different situation from a child who jumped from the 40th to the 85th percentile in one year. Pediatricians look for:

• Stable tracking: Following roughly the same percentile curve over time (healthy sign)
• Crossing up: Moving to a significantly higher percentile curve (may warrant attention)
• Crossing down: Dropping to a significantly lower percentile curve (may indicate illness, inadequate nutrition, or other concerns)

Calculate Your Child’s BMI Percentile →

CDC vs. WHO Growth Charts

Two sets of growth charts are commonly used, and they serve different purposes:

In the United States, the current recommendation is to use WHO charts for children under 2 and CDC charts for children ages 2–19. Internationally, many countries use WHO charts for all ages up to 5 and then local or WHO references for older children. For a detailed guide on understanding BMI percentiles, see our BMI percentile calculator guide.

Healthy Weight Ranges for Children by Age

The following table shows approximate weight ranges corresponding to the healthy BMI percentile range (5th–84th) at average heights for each age. These are general reference values — your child’s healthy weight depends on their individual height.

Boys: Healthy Weight at Average Height

Girls: Healthy Weight at Average Height

Childhood Obesity: Prevalence and Health Risks

Childhood obesity has become a major public health concern. According to CDC data, approximately 19.7% of U.S. children and adolescents ages 2–19 have obesity (BMI at or above the 95th percentile), with an additional 16.1% classified as overweight (85th to 94th percentile). Rates have more than tripled since the 1970s. Mayo Clinic notes that childhood obesity can lead to serious health problems that were once confined to adults.

Obesity Rates by Age Group (U.S.)

Health Risks of Childhood Obesity

Children with obesity face both immediate and long-term health consequences:

• Type 2 diabetes: Once considered an adult disease, type 2 diabetes is now diagnosed in children as young as 10. The risk rises sharply above the 95th BMI percentile.
• Cardiovascular risk factors: High blood pressure, elevated cholesterol, and early arterial changes can be detected in obese children.
• Asthma: Obesity increases asthma risk and severity in children.
• Joint problems: Excess weight stresses developing joints, particularly the hips and knees. Slipped capital femoral epiphysis (a hip condition) is strongly associated with obesity.
• Sleep apnea: Obstructive sleep apnea is common in obese children and can impair school performance.
• Fatty liver disease: Non-alcoholic fatty liver disease is now the most common liver condition in children.
• Psychosocial effects: Bullying, low self-esteem, depression, and anxiety are significantly more common in children with obesity.
• Adult obesity: Approximately 80% of obese adolescents become obese adults, carrying these health risks into adulthood.

Childhood Underweight: When to Be Concerned

While obesity receives more attention, being underweight (below the 5th percentile) also warrants evaluation. Potential causes include:

• Inadequate caloric intake: Picky eating, food insecurity, or restrictive diets
• Malabsorption: Celiac disease, food allergies, or other gastrointestinal conditions
• Chronic illness: Conditions like cystic fibrosis, chronic infection, or inflammatory bowel disease
• Eating disorders: Anorexia nervosa can emerge in children as young as 8–10
• Constitutional thinness: Some children are naturally thin due to genetics, especially if parents are lean
• Growth delays: Late puberty or growth hormone deficiency

A single reading below the 5th percentile does not necessarily indicate a problem. The key is whether the child is growing consistently along their own curve and meeting developmental milestones. A sudden drop across percentile lines is more concerning than a child who has always tracked along the 3rd percentile.

Puberty and BMI Changes

Puberty causes significant BMI changes that can be confusing for parents:

Girls

Girls typically enter puberty between ages 8 and 13 (average age of onset around 10–11). During puberty, girls naturally gain body fat, particularly in the hips, thighs, and breasts. This normal fat gain causes BMI to increase. A girl whose BMI rises from the 50th to the 65th percentile during puberty is usually experiencing normal development, not becoming overweight. Girls gain an average of 15–20 lbs of fat during puberty — this is biologically normal and necessary for reproductive development.

Boys

Boys typically enter puberty between ages 9 and 14 (average around 11–12). Boys tend to gain proportionally more muscle than fat during puberty. A boy whose BMI increases during puberty may be gaining muscle mass (especially if physically active), which is healthy but still raises the BMI number. Boys who are early maturers may temporarily have higher BMI percentiles than their late-maturing peers, which often evens out by age 16–18.

Timing Differences

Because children develop at different rates, BMI percentiles can be misleading during the pubertal years (roughly ages 10–15). An early-maturing 11-year-old girl may have a much higher BMI than a late-maturing peer, not because she is less healthy, but because she is further along in development. This is one reason pediatricians assess pubertal stage (Tanner stage) alongside BMI.

BMI Limitations in Children

Pediatric BMI shares the limitations of adult BMI, with some additional issues specific to growing children:

• Does not measure body fat directly: A muscular, athletic child can have a high BMI percentile while carrying very little excess fat. This is particularly common in children involved in sports like gymnastics, swimming, or wrestling.
• Does not account for growth tempo: Children who mature early will temporarily have higher BMI than late maturers. BMI charts were built from cross-sectional data (measuring many children at one time point), not longitudinal tracking of individual growth patterns.
• Cultural and ethnic variation: The CDC growth charts are based primarily on U.S. data and may not accurately represent healthy growth patterns in all ethnic groups. Asian children, for example, may carry higher health risk at lower BMI percentiles than the charts suggest.
• Not useful under age 2: For infants and toddlers, weight-for-length charts are used instead of BMI-for-age. The BMI formula becomes unreliable at very young ages because of the rapid changes in body proportions.
• Percentile ceiling effect: The CDC charts top out at the 97th percentile. For severely obese children, the percentage of the 95th percentile (e.g., 120% of the 95th) is used to differentiate degrees of severe obesity, but this extended system is less precise.

Tips for Parents

When to See Your Pediatrician

Schedule a discussion about your child’s weight if:

• Your child’s BMI is above the 85th percentile or below the 5th percentile
• Their BMI percentile has jumped significantly (crossing two or more major percentile lines) within the past year
• Your child shows signs of early puberty (before age 8 in girls, before age 9 in boys) combined with rapid weight gain
• There is a family history of type 2 diabetes, heart disease, or severe obesity
• Your child has symptoms like excessive thirst, frequent urination, snoring, or joint pain
• Your child is restricting food, has an intense fear of gaining weight, or shows signs of disordered eating
• Your child’s weight is affecting their daily life, social interactions, or emotional well-being

For more about how age affects BMI interpretation across the full lifespan, see our BMI Calculator by Age guide.

Frequently Asked Questions

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Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. BMI is a screening tool, not a diagnostic measure. Always consult a qualified healthcare provider for personalized health assessment and recommendations regarding your child’s growth and development.