BMI Calculator (Body Mass Index)


Calculate your BMI

Use the BMI calculator above to determine your Body Mass Index and understand what it means for your health.



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What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a numerical value calculated from a person’s weight and height. It is widely used as a screening tool to assess whether an individual has a healthy body weight in relation to their height.

BMI is recommended by the World Health Organization (WHO) as a standard method for identifying underweight, overweight, and obesity in adults.

How is BMI calculated?

The formula used to calculate Body Mass Index is:

BMI = weight (kg) / [height (m)]²

For example, a person who weighs 70 kilograms and is 1.70 meters tall will have a BMI of approximately 24.2.

How we calculate & interpret BMI (Adults vs Children)

Body Mass Index (BMI) is calculated using the same mathematical formula for all ages. However, the way BMI values are interpreteddiffers significantly between adults and children due to growth, development, and body composition changes over time.

BMI calculation (all ages)

The BMI formula is based only on height and weight:

BMI = weight (kg) / [height (m)]²

This formula produces a numerical value that represents body weight relative to height. The calculation itself does not change based on age or gender.

BMI interpretation for adults (age 20+)

For adults, BMI is interpreted using fixed numerical rangesdefined by international health organizations. These ranges are the same for men and women and do not change with age.

Adult BMI categories classify weight status (such as underweight, normal weight, overweight, or obesity) and are commonly used as ascreening tool to assess potential health risks.

BMI interpretation for children and teenagers (under 20)

In children and adolescents, BMI values are interpreted differently. Because children are still growing, their BMI is compared againstage- and sex-specific percentile charts rather than fixed numeric thresholds.

A child’s BMI percentile shows how their BMI compares to others of the same age and biological sex. This approach accounts for normal growth patterns and developmental differences.

This calculator applies recognized BMI-for-age percentile standards to provide age-appropriate interpretations for children and teenagers.

Important: While BMI is useful for population-level screening and general guidance, it does not measure body fat directly and should not be used as a standalone diagnostic tool.

For a more complete health assessment, BMI results should be interpreted alongside other factors such as age, lifestyle, body composition, and professional medical evaluation.

BMI categories for adults

  • Underweight: BMI below 18.5
  • Normal weight: BMI between 18.5 and 24.9
  • Overweight: BMI between 25 and 29.9
  • Obesity: BMI 30 or higher

These BMI ranges apply to adults aged 20 years and older, regardless of gender.

BMI for children and teenagers

For children and adolescents under the age of 20, BMI is interpreted differently than for adults. Instead of fixed ranges, BMI values are compared against age- and sex-specific percentile charts.

This BMI calculator uses real medical BMI percentile tables for children and teenagers, ensuring an accurate and age-appropriate interpretation.

Differences between men and women

While the BMI formula is the same for both men and women, body composition differs between sexes. Men generally have more muscle mass, while women tend to have a higher percentage of body fat.

Because of this, BMI should always be interpreted alongside other health indicators such as age, lifestyle, and overall body composition.

Limitations of BMI

  • BMI does not distinguish between muscle and fat mass
  • It may overestimate body fat in muscular individuals
  • It does not account for fat distribution
  • It should not be used as a sole diagnostic tool

For a complete health assessment, BMI should be combined with other measurements such as waist circumference, body fat percentage, and medical evaluation.

Sources & further reading

The information and calculations used in this BMI Calculator are based on widely accepted medical references and public health guidelines. The sources below provide additional context about how Body Mass Index is calculated and interpreted for both adults and children.

These references are provided for educational purposes only. Body Mass Index is a screening tool and should not be used as a sole method for diagnosing health conditions.

Frequently Asked Questions about BMI

What does BMI actually measure?

BMI estimates body weight relative to height. It does not measure body fat directly, but it helps identify weight categories that may be associated with potential health risks at a population level.

Is BMI accurate for everyone?

BMI is a useful screening tool for most adults, but it may be less accurate for athletes, older adults, pregnant individuals, or people with atypical body composition.

Why is BMI interpreted differently for children?

Children and teenagers are still growing, so their BMI is compared to age- and sex-specific percentile charts instead of fixed ranges. This accounts for normal growth and development patterns.

Does BMI differ between men and women?

The BMI formula is the same for men and women. However, differences in muscle mass and fat distribution mean BMI results should be interpreted alongside other health indicators.

Can BMI tell me if I am healthy?

BMI alone cannot determine overall health. It should be considered together with lifestyle factors, physical activity, medical history, and, when appropriate, professional medical advice.

How often should I check my BMI?

BMI is best used to track trends over time rather than as a one-time result. Checking it periodically can help monitor long-term changes.

Why can two people with the same BMI look very different?

BMI does not account for muscle mass, bone density, or fat distribution. Two individuals with the same BMI may have very different body compositions.

Should I rely on BMI instead of medical advice?

No. BMI calculators provide educational estimates only. For personalized guidance or health concerns, a qualified healthcare professional should always be consulted.

Medical Disclaimer

This BMI Calculator provides estimates of body mass index (BMI) for educational purposes. It is not medical advice and does not replace consultation with a healthcare professional. Results may vary for children, pregnant women, athletes, or people with medical conditions. Always consult your doctor for personalized guidance.