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 standard BMI formula:

Where:

• \( weight \) — Body weight in kilograms
• \( height \) — Height in meters

Note: For children, the raw BMI number must be plotted on age- and sex-specific growth charts to determine the percentile.

3. Importance of BMI for Children

Details: BMI-for-age is the recommended measure for assessing weight status in children and teens aged 2-18 years. It helps identify potential weight problems that may lead to health issues.

4. Using the Calculator

Tips: Enter weight in kilograms, height in meters, age in years (2-18), and select gender. For accurate results, measurements should be taken with minimal clothing and no shoes.

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 do the percentile ranges mean?
A: Underweight (<5th), Healthy weight (5th-85th), Overweight (85th-95th), Obese (>95th). These are general guidelines - consult a healthcare professional for individual assessment.

Q3: When should I be concerned about my child's BMI?
A: If your child's BMI is below the 5th percentile or above the 85th percentile, or if there are sudden changes in BMI percentile over time.

Q4: Are there limitations to BMI for children?
A: BMI doesn't distinguish between fat and muscle mass. Athletic children may have high BMI due to muscle rather than fat.

Q5: Where can I find NHS growth charts?
A: NHS growth charts are available at RCPCH website or through your GP.