1. What is the BMI Percentile Calculator?

The BMI percentile calculator for children and teens uses the LMS method to determine how a child's BMI compares to others of the same age and gender. Unlike adults, children's BMI needs to be interpreted relative to growth charts.

2. How Does the Calculator Work?

The calculator uses the LMS method:

Where:

• \( BMI \) — Body Mass Index (kg/m²)
• \( M \) — Median BMI for age and gender
• \( L \) — Box-Cox power (skewness)
• \( S \) — Coefficient of variation
• \( \Phi \) — Standard normal cumulative distribution

Explanation: The LMS method transforms BMI to a normal distribution using age- and gender-specific parameters from growth charts.

3. Importance of BMI Percentile

Details: BMI percentile is the preferred measure for assessing weight status in children and teens. It helps identify underweight, healthy weight, overweight, and obesity.

4. Using the Calculator

Tips: Enter BMI in kg/m², age in years (can include decimals for months), and select gender. The calculator will show the percentile ranking compared to children of the same age and gender.

5. Frequently Asked Questions (FAQ)

Q1: What do the percentiles mean?
A: Below 5th percentile is underweight, 5th-85th is healthy weight, 85th-95th is overweight, and above 95th is obese.

Q2: Why use percentiles instead of BMI categories like adults?
A: Children's body composition changes with growth, so comparison to peers of same age and sex is more meaningful.

Q3: Where do the L, M, S values come from?
A: They are derived from large national growth surveys like the CDC or WHO growth charts.

Q4: Is this calculator accurate for all ages?
A: It's designed for ages 2-20. BMI is not recommended for infants under 2 years.

Q5: How often should BMI be checked in children?
A: Annually is typical, but more frequent monitoring may be needed if weight concerns exist.