1. What is BMI?

Body Mass Index (BMI) is a measure that uses height and weight to work out if 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 BMI formula:

Where:

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

Explanation: The BMI calculation divides an adult's weight in kilograms by their height in meters squared. For children and teens, the BMI number is plotted on the CDC BMI-for-age growth charts to determine weight status.

3. Importance of BMI Calculation

Details: BMI is a screening tool that can indicate whether a child is underweight, healthy weight, overweight, or obese. However, it's not a diagnostic tool and should be followed up with further assessment.

4. Using the Calculator

Tips: Enter weight in kg, 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: Why is BMI different for children?
A: Children's body composition varies as they grow, so BMI is interpreted relative to other children of the same age and sex.

Q2: What are healthy BMI ranges for children?
A: Healthy ranges vary by age and gender. Results should be plotted on growth charts to determine percentiles.

Q3: How accurate is BMI for children?
A: BMI is a good screening tool but doesn't measure body fat directly. Athletic children may have high BMI due to muscle.

Q4: How often should children's BMI be checked?
A: The NHS recommends measuring children's height and weight annually as part of routine health checks.

Q5: Where can I find NHS BMI charts?
A: NHS BMI percentile charts are available through your GP or on the NHS website for tracking growth patterns.