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Tính BMI cho trẻ 2-19 tuổi và xem phần trăm theo tuổi và giới tính.
Unlike adults, children's BMI is interpreted using percentile charts that account for age and sex. A child's BMI is plotted on a growth chart and compared to other children of the same age and sex. This is necessary because children's body composition changes as they grow — it's normal for BMI to fluctuate during childhood development. The CDC growth charts, based on data from national surveys, are used as the standard reference.
For children aged 2-19, BMI categories are: Underweight (below 5th percentile), Healthy weight (5th to 85th percentile), Overweight (85th to 95th percentile), and Obese (95th percentile or above). A child at the 75th percentile has a BMI higher than 75% of children the same age and sex. Being at a higher percentile doesn't automatically mean unhealthy — context matters.
BMI naturally changes during childhood. Babies typically have high BMI that decreases through preschool years, reaching its lowest point around age 5-6 (called the 'adiposity rebound'). An early adiposity rebound (before age 5) may predict higher BMI later. During puberty (typically 10-14 for girls, 12-16 for boys), body composition changes significantly — girls gain more fat while boys gain more muscle.
Childhood obesity has tripled since the 1970s in many countries. Contributing factors include increased screen time, reduced physical activity, larger portion sizes, and more processed food consumption. Prevention strategies include: at least 60 minutes of physical activity daily, limiting screen time to 2 hours, serving fruits and vegetables at every meal, avoiding sugary drinks, family meals at the table, and adequate sleep (9-11 hours for school-age children).
Consult your child's doctor if: their BMI is below the 5th or above the 85th percentile, there's a significant change in BMI percentile between checkups, your child shows signs of disordered eating, they're experiencing bullying related to weight, or you're concerned about growth patterns. Pediatricians can assess overall health, order appropriate tests, and provide guidance tailored to your child's specific situation.
Focus on healthy behaviors rather than weight numbers. Avoid putting children on restrictive diets — growing bodies need adequate nutrition. Model healthy eating as a family. Make physical activity fun (play, sports, family walks). Avoid using food as reward or punishment. Build self-esteem and body positivity regardless of size. If weight management is needed, work with a pediatric healthcare team to ensure nutritional needs are met while supporting healthy growth.
BMI assessment in children requires age-and-sex-specific reference charts because body composition changes dramatically during growth and development. The CDC growth charts, developed from national survey data, provide the standard reference for children aged 2-19 in the United States, while the WHO charts are used internationally for children under 5.
The adiposity rebound — the point at which BMI begins to increase after its nadir in early childhood — is a critical period. Research shows that an early adiposity rebound (before age 5) is associated with higher BMI and increased obesity risk later in life. Tracking this pattern helps pediatricians identify children who may benefit from early lifestyle interventions.
Puberty significantly complicates BMI interpretation. Girls typically gain body fat as part of normal pubertal development, with body fat increasing from about 16% to 25%. Boys typically gain lean mass, with body fat often decreasing. These natural changes mean that BMI percentile shifts during puberty don't necessarily indicate health problems and should be interpreted in context.
Recent research has questioned whether BMI percentiles adequately capture cardiometabolic risk in children. Some studies suggest that waist-to-height ratio may be a better predictor of metabolic syndrome risk in pediatric populations. However, BMI percentiles remain the standard clinical tool due to their simplicity, established reference data, and strong correlation with health outcomes at the population level.
Children's BMI is calculated the same as adults: weight (kg) ÷ height² (m²). The difference is interpretation: the calculated BMI is plotted on age-and-sex-specific percentile charts. The CDC uses growth charts based on national data from 1963-1994 (before the obesity epidemic significantly shifted population norms).
Percentile categories: Below 5th = Underweight, 5th-84th = Healthy weight, 85th-94th = Overweight, 95th+ = Obese. Z-scores (standard deviations from the mean) are increasingly used for children with very high or very low BMIs where percentiles become less precise.