1. What is BMI?

BMI (Body Mass Index) is a measure that uses height and weight to work out if a person's weight is healthy. For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age.

2. How Does the Calculator Work?

The calculator uses the standard BMI formula:

Where:

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

Note: For children, the BMI number is plotted on growth charts to determine a percentile ranking.

3. Importance of BMI Calculation for Children

Details: BMI-for-age is the recommended measure for screening overweight and obesity in children aged 2-18 years. It accounts for normal differences in body fat between boys and girls and differences in body fat at various ages.

4. Using the Calculator

Tips: Enter weight in kilograms, height in meters, age in years (2-18), and select gender. All values must be valid (weight > 0, height > 0, age between 2-18).

5. Frequently Asked Questions (FAQ)

Q1: How is BMI interpreted for children?
A: BMI-for-age is plotted on growth charts to determine a percentile ranking. Percentiles show how a child's BMI compares to others of the same age and sex.

Q2: What are the BMI percentile categories?
A: Underweight (<5th), Healthy weight (5th-85th), Overweight (85th-95th), Obese (≥95th).

Q3: Why use BMI-for-age instead of regular BMI?
A: Children's body composition changes as they grow, and differs between boys and girls. BMI-for-age accounts for these differences.

Q4: How often should children's BMI be checked?
A: The NHS recommends annual BMI checks for children aged 2-18 as part of routine health assessments.

Q5: Are there limitations to BMI-for-age?
A: It doesn't distinguish between fat and muscle mass. Very muscular children may have a high BMI without excess fat.