1. What is BMI?

Body Mass Index (BMI) is a person's weight in kilograms divided by the square of height in meters. It's a screening tool that may indicate whether a person is underweight, healthy weight, overweight, or obese.

2. How BMI is Calculated

The BMI formula is simple:

Where:

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

Example: For a woman who weighs 65 kg and is 1.68 m tall: 65 ÷ (1.68 × 1.68) = 23.0 kg/m²

3. Age-Specific Interpretation

For adults (20+ years):

• Underweight: BMI < 18.5
• Normal weight: BMI 18.5-24.9
• Overweight: BMI 25-29.9
• Obese: BMI ≥ 30

For children/teens (2-19 years): BMI is compared to growth charts for age and sex:

• Underweight: <5th percentile
• Healthy weight: 5th to 85th percentile
• Overweight: 85th to 95th percentile
• Obese: ≥95th percentile

4. Using the Calculator

Tips: Enter weight in kilograms, height in meters, and exact age. For children, results are based on CDC growth charts.

5. Frequently Asked Questions (FAQ)

Q1: Why is BMI interpretation different for children?
A: Children's body composition varies with age and sex, so BMI must be compared to peers of same age and sex.

Q2: Are there limitations to BMI?
A: Yes. BMI doesn't distinguish between muscle and fat, and may not reflect body fat distribution.

Q3: What's a healthy BMI for older women?
A: For women over 65, a BMI of 23-27 may be healthier than lower BMIs, as some extra weight may protect against osteoporosis.

Q4: How often should BMI be checked?
A: For adults, annually is sufficient. For growing children, every 3-6 months may be appropriate.

Q5: Where can I find official growth charts?
A: CDC growth charts are available at: https://www.cdc.gov/growthcharts/