BMI Calculator (Body Mass Index)

    Discover if you are at your ideal weight in less than 10 seconds.

    Written by Felipe Spirola (Health Tech Specialist)Reviewed by FitBalanceCalc Editorial BoardUpdated 2026-06-20

    Calculate my BMI now

    Based on World Health Organization (WHO) guidelines

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    BMI Table by Age and Sex

    See how your result compares to detailed classification charts by age group and gender.

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    Quick Answers (Zero-Click FAQ)

    What is a normal BMI for a 40-year-old woman?

    A normal BMI for a 40-year-old woman ranges from 18.5 to 24.9. While the calculation (weight divided by height squared) is identical across ages, biological changes after 40 can impact body composition, making it crucial to evaluate BMI alongside waist circumference and muscle mass.

    What is the normal BMI for a 50-year-old man?

    The normal BMI range for a 50-year-old man is 18.5 to 24.9. However, research suggests that for men over 50, a slightly higher BMI (up to 27) can be protective as it provides nutritional reserves and correlates with lower mortality rates.

    Male vs Female BMI: Is there a difference?

    The mathematical formula for the Body Mass Index (BMI) is exactly the same for men and women. The calculation does not change: weight divided by height squared. However, the **interpretation of the results** requires attention to natural physiological differences between the sexes. Men tend to have more muscle mass, which is denser than fat, and this can increase BMI even with low levels of adiposity. Women, on the other hand, naturally possess a higher percentage of healthy body fat due to reproductive and hormonal factors. Therefore, while the WHO BMI table serves as a good initial parameter for both, BMI should always be evaluated in conjunction with complementary measures, such as waist circumference and fat percentage, for an accurate health diagnosis.

    What is BMI?

    Body Mass Index (BMI) is an international measure used to calculate whether a person is at an ideal weight. Developed by polymath Lambert Quételet in the 19th century, it is a simple and quick method to indirectly assess body fat levels. While it doesn't measure fat directly, BMI correlates with direct fat measurements and is widely used by doctors and nutritionists to identify issues such as malnutrition, overweight, and obesity in adult populations.

    How to calculate BMI

    The BMI calculation is done by dividing weight (in kilograms) by height squared (in meters). The mathematical formula is: **BMI = weight / (height x height)**. For example, if you weigh 70kg and are 1.70m tall, the calculation would be: 70 / (1.70 * 1.70) = 70 / 2.89 = 24.22. This result indicates that the person is in the normal weight range.

    WHO BMI Table

    The World Health Organization uses a standard table to classify the nutritional status of adults. This classification helps understand the health risks associated with each weight range.

    IMCClassificação
    Below 18.5Underweight
    18.5 - 24.9Normal Weight
    25.0 - 29.9Overweight
    30.0 - 34.9Obesity Class I
    35.0 - 39.9Obesity Class II
    Above 40.0Obesity Class III

    BMI Limitations

    BMI is a valuable tool, but it has important limitations. It does not differentiate muscle mass from fat mass. Therefore, a high-performance athlete may have an 'overweight' BMI due to muscle, even with very low body fat. Additionally, BMI does not consider body fat distribution. Visceral (abdominal) fat is much more dangerous for cardiovascular health than subcutaneous fat in other areas.

    How to improve your BMI

    If your result is outside the normal range, the first step is to seek guidance from a healthcare professional. Improving BMI usually involves a combination of a balanced diet and regular physical activity. Focusing on food quality, reducing intake of ultra-processed foods, and increasing fiber and protein intake helps with weight control. Staying active, even with daily walks, already brings significant health benefits and helps maintain BMI at healthy levels.

    Frequently Asked Questions about BMI

    Get your questions about BMI, calories, and health answered

    💡 Still have questions?

    Remember: FitBalanceCalc is an educational tool. for personalized guidance on diet, exercise, or specific medical issues, always seek qualified health professionals such as nutritionists, physical educators, and doctors.

    Sources & Scientific References

    1. [1]World Health Organization (WHO). BMI classification. WHO Expert Consultation. Lancet, 363(9403):157–163, 2004.
    2. [2]National Heart, Lung, and Blood Institute (NHLBI). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication No. 98-4083. 1998.
    3. [3]Centers for Disease Control and Prevention (CDC). About Adult BMI. Available at: https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html

    ⚠ Legal Disclaimer

    FitBalanceCalc provides calculation tools based on international public health guidelines. This data is strictly informational and educational in nature and does not replace medical diagnosis, medical guidance, or the supervision of nutritionists and physical education professionals.