Understanding BMI and Its Calculation
Understand what Body Mass Index (BMI) is, how it’s calculated, and what your BMI means for your health. Learn how to assess your weight status and maintain a healthy BMI.
Written by Dr. J T Hema Pratima
Reviewed by Dr. D Bhanu Prakash MBBS, AFIH, Advanced certificate in critical care medicine, Fellowship in critical care medicine
Last updated on 13th Aug, 2025
Maintaining a healthy weight is essential for overall well-being, and one of the most common tools used to assess weight status is the Body Mass Index (BMI). Whether you're trying to lose weight, gain muscle, or simply stay healthy, understanding BMI can help you make informed decisions about your health.
What is BMI?
BMI, or Body Mass Index, is a simple calculation that estimates whether a person has a healthy body weight based on their height and weight. It is a widely used screening tool to identify potential weight-related health risks.
### How is BMI Calculated?
BMI is calculated using the following formula:
BMI = Weight (kg) / (Height (m))²
For example, if you weigh 70 kg and your height is 1.75 m, your BMI would be:
70 / (1.75 × 1.75) = 22.86
If you prefer using pounds and inches, the formula is:
BMI = (Weight (lbs) / (Height (in))²) × 703
Once you calculate your BMI, it falls into one of the following categories:
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Understanding BMI Categories
| BMI Range | Category |
|----------------|----------------------|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy Weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obesity |
Why is BMI Important?
BMI is a useful tool because:
1. Identifies Health Risks – A high BMI may indicate an increased risk of conditions like diabetes, heart disease, and high blood pressure. A low BMI could suggest malnutrition or other health concerns.
2. Helps Track Progress – If you're working toward weight loss or muscle gain, BMI can help monitor changes.
3. Guides Medical Advice – Doctors use BMI to recommend lifestyle changes, dietary adjustments, or further medical tests.
Limitations of BMI
While BMI is helpful, it doesn’t tell the whole story:
- Doesn’t Measure Body Fat – BMI doesn’t distinguish between fat, muscle, or bone density. Athletes with high muscle mass may have a high BMI but low body fat.
- Doesn’t Consider Age or Gender – Older adults may naturally have higher body fat, and women tend to have more body fat than men at the same BMI.
- Not Suitable for Children – Kids and teens use age- and sex-specific BMI growth charts.
How to Maintain a Healthy BMI
If your BMI falls outside the healthy range, here are some ways to improve it:
- For Underweight Individuals (BMI < 18.5)
- Eat nutrient-dense foods (nuts, dairy, lean proteins).
Include healthy fats (avocados, olive oil).
Strength training to build muscle.
- For Overweight or Obese Individuals (BMI ≥ 25)
- Balanced Diet – Focus on whole grains, lean proteins, fruits, and vegetables.
- Regular Exercise – Aim for at least 150 minutes of moderate activity per week.
- Portion Control – Avoid overeating by monitoring serving sizes.
- Stay Hydrated – Drink plenty of water to avoid mistaking thirst for hunger.
- For Those in the Healthy Range (BMI 18.5–24.9)
- Maintain your current habits with a balanced diet and regular exercise.
- Monitor weight changes periodically.
When to Consult a Doctor
If your BMI suggests you are underweight, overweight, or obese, it’s a good idea to consult a healthcare provider. They can assess other factors like body fat percentage, diet, and lifestyle to give personalized advice.
Book a Consultation with Apollo 24|7
If you're concerned about your weight or BMI, Apollo 24|7 offers expert consultations with nutritionists and doctors. You can also schedule a body composition analysis for a more detailed assessment.
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Conclusion
BMI is a helpful starting point for understanding your weight status, but it’s not the only factor in health. Combining BMI with other assessments like waist circumference, diet, and activity levels provides a clearer picture of your well-being. By making small, sustainable changes to your diet and lifestyle, you can achieve and maintain a healthy BMI, leading to better energy levels, improved mood, and reduced risk of chronic diseases.
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