1. What is BMI for Children?

Body Mass Index (BMI) is a measure that uses height and weight to estimate body fat. For children and infants, BMI is age and sex-specific and is referred to as BMI-for-age. The NHS uses growth charts to compare a child's BMI with children of the same age and sex.

2. How the Calculator Works

The calculator uses the standard BMI formula adjusted for child growth percentiles:

Where:

• \( weight \) — Measured in kilograms (kg)
• \( height \) — Measured in meters (m)

Explanation: The result is compared to UK growth charts to determine the percentile for the child's age and gender.

3. Importance of BMI Calculation

Details: Tracking BMI-for-age helps identify potential weight problems in children. However, it's just one indicator and should be considered alongside other growth measurements and professional assessment.

4. Using the Calculator

Tips: Enter weight in kg, height in meters, and exact age in years. For infants under 2 years, length should be measured lying down rather than standing height.

5. Frequently Asked Questions (FAQ)

Q1: How is child BMI different from adult BMI?
A: Children's BMI is interpreted relative to other children of the same age and sex, using percentile charts rather than fixed categories.

Q2: What is a healthy BMI percentile for children?
A: Generally, 5th to 85th percentile is considered healthy weight, though this should be assessed by a healthcare professional.

Q3: Why are different charts used for infants?
A: Infants grow rapidly and have different body proportions, so special growth standards (like WHO charts) are used for under 2s.

Q4: Can BMI be misleading for children?
A: Yes, BMI doesn't distinguish between fat and muscle, so athletic children may appear overweight. Professional assessment is important.

Q5: How often should my child's BMI be checked?
A: Routine measurements are typically done at NHS health checks (around ages 1, 2-2.5, and 5), or more frequently if concerns exist.