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Body Mass Index (BMI) Calculator

function calculateBMI() { var weight = parseFloat(document.getElementById('weight_input').value); var height = parseFloat(document.getElementById('height_input').value); var resultBox = document.getElementById('bmi_result_box'); var valueDisplay = document.getElementById('bmi_value'); var categoryDisplay = document.getElementById('bmi_category'); var descriptionDisplay = document.getElementById('bmi_description'); if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) { alert('Please enter valid positive numbers for both weight and height.'); return; } var heightInMeters = height / 100; var bmi = (weight / (heightInMeters * heightInMeters)).toFixed(1); valueDisplay.innerHTML = 'Your BMI: ' + bmi; resultBox.style.display = 'block'; var category = ''; var color = ''; var desc = ''; if (bmi = 18.5 && bmi = 25 && bmi <= 29.9) { category = 'Overweight'; color = '#f39c12'; desc = 'You are slightly above the healthy range. Maintaining a balanced diet and regular physical activity can help manage your weight.'; } else { category = 'Obese'; color = '#e74c3c'; desc = 'Your BMI falls within the obese range. This may increase risk for certain health conditions. It is recommended to speak with a doctor.'; } categoryDisplay.innerHTML = category; categoryDisplay.style.color = color; descriptionDisplay.innerHTML = desc; }

Understanding Body Mass Index (BMI)

Body Mass Index (BMI) is a screening tool used to estimate a person's total body fat based on their height and weight. While it does not measure body fat directly, it provides a reliable indicator of potential health risks associated with being underweight, overweight, or obese.

The BMI Formula

The BMI calculation used by health professionals worldwide is standard across all adult populations. It is calculated using the following metric formula:

BMI = weight (kg) / [height (m)]²

Standard BMI Categories

BMI Range Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal or Healthy Weight
25.0 – 29.9 Overweight
30.0 and Above Obese

Example Calculations

  • Example 1: An adult weighing 70kg at a height of 175cm (1.75m). Calculation: 70 / (1.75 * 1.75) = 22.9 BMI (Healthy Weight).
  • Example 2: An adult weighing 90kg at a height of 180cm (1.80m). Calculation: 90 / (1.80 * 1.80) = 27.8 BMI (Overweight).
  • Example 3: An adult weighing 50kg at a height of 165cm (1.65m). Calculation: 50 / (1.65 * 1.65) = 18.4 BMI (Underweight).

Important Considerations

While BMI is a useful starting point, it has limitations. It does not account for muscle mass, bone density, or overall body composition. Athletes with high muscle mass may have a high BMI but very low body fat. Conversely, elderly individuals may have a "normal" BMI but lower muscle mass and higher body fat percentage. Always consult with a medical professional for a comprehensive health assessment.

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