BMI Calculator — Calculate Your Body Mass Index Online
Calculate your Body Mass Index and health category
The BMI (Body Mass Index) Calculator measures your body weight relative to your height to classify whether you are underweight, normal weight, overweight, or obese. While BMI is not a perfect health measure, it is widely used by doctors, dieticians, and health insurance companies as a quick screening tool.
1What Is BMI and How Is It Calculated?
BMI is calculated using the formula: BMI = Weight (kg) ÷ Height² (m²). For example, if you weigh 70 kg and are 175 cm tall: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9. This falls in the "Normal weight" range. WHO classifies BMI as: Below 18.5 = Underweight, 18.5–24.9 = Normal weight, 25.0–29.9 = Overweight, 30.0 and above = Obese. Some Asian health guidelines use slightly stricter cutoffs (23 for overweight, 27.5 for obese) as Asians tend to carry more visceral fat at lower BMIs.
2Limitations of BMI
BMI is a screening tool, not a diagnostic measure. It has important limitations: it doesn't distinguish between muscle mass and fat mass (athletes may have high BMI but low body fat), doesn't account for fat distribution (visceral vs subcutaneous), doesn't consider age-related muscle loss in elderly, and doesn't reflect hormonal or metabolic health. Two people with the same BMI can have very different health profiles. Waist circumference, waist-to-hip ratio, and body fat percentage provide additional health insights.
3BMI for Different Age Groups
For children and teenagers (2–19 years), BMI is plotted on age and sex-specific growth charts as BMI-for-age percentiles, since body composition changes during growth. For adults 20+, the standard BMI cutoffs apply. For older adults (65+), slightly higher BMI (25–27) may be protective against bone loss and early death. Pregnancy significantly affects weight and BMI should not be used during pregnancy.
4Healthy Ways to Reach Ideal BMI
If your BMI is outside the normal range, gradual and sustainable changes are most effective. For weight loss: aim for 0.5–1 kg per week through a combination of moderate caloric deficit (300–500 kcal/day) and exercise. Crash diets are counterproductive. For underweight: focus on nutrient-dense calorie-rich foods and strength training. Always consult a registered dietician or doctor before starting any weight management program.
Frequently Asked Questions
The WHO standard for normal BMI is 18.5–24.9. However, guidelines by the Indian Council of Medical Research (ICMR) and WHO for Asian populations suggest a lower threshold: 18.5–22.9 as normal, 23–24.9 as overweight, and 25+ as obese, due to higher metabolic risk at lower BMI values in Asian populations.