BMI Calculator
Calculate your Body Mass Index and understand your weight category
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BMI is a useful screening tool, but it doesn't diagnose body fatness or health. Consider factors like muscle mass, age, and gender when interpreting results.
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Fill in your weight and height to calculate your BMI
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References
- World Health Organization (WHO) - BMI Classification
- National Institutes of Health (NIH) - Clinical Guidelines on Body Composition
- Centers for Disease Control and Prevention (CDC) - Healthy Weight & Body Fat Assessment
What is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple, widely-used screening tool that estimates whether your weight is healthy relative to your height. It was invented in the 1830s by Belgian mathematician Adolphe Quetelet and remains the most common method for categorizing weight status worldwide.
BMI does not measure body fat directly, but research shows it correlates reasonably well with more direct measures of body fatness. It is used by doctors, health organizations, and fitness professionals as an initial assessment of weight-related health risk.
How is BMI Calculated?
The BMI formula is straightforward:
BMI = weight (kg) ÷ height (m)²
Example calculation: If you weigh 70 kg and your height is 1.75 m:
For imperial units (pounds and inches), the formula is:
BMI = weight (lbs) ÷ height (in)² × 703
Our calculator above handles both unit systems automatically — simply select your preferred units and enter your measurements.
BMI Categories and Weight Status
The World Health Organization (WHO) classifies BMI into the following categories for adults:
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of nutrient deficiencies, weakened immune system, bone loss |
| 18.5 – 24.9 | Normal Weight | Lowest risk of chronic disease. Associated with optimal health outcomes |
| 25.0 – 29.9 | Overweight | Moderately increased risk of heart disease, type 2 diabetes, high blood pressure |
| 30.0 – 34.9 | Obese (Class I) | High risk of cardiovascular disease, diabetes, joint problems |
| 35.0 – 39.9 | Obese (Class II) | Very high risk of serious health complications |
| 40.0 or above | Obese (Class III) | Extremely high risk. Severe obesity significantly impacts quality of life |
Health Risks Associated with High BMI
Carrying excess weight, as indicated by a high BMI, is associated with significantly increased risk of numerous chronic diseases:
- •Cardiovascular Disease: Heart disease, stroke, high blood pressure, and elevated cholesterol levels
- •Type 2 Diabetes: Excess weight increases insulin resistance and blood sugar levels
- •Sleep Apnea: Weight around the neck can obstruct airways during sleep
- •Joint Problems: Extra weight puts stress on knees, hips, and lower back, increasing arthritis risk
- •Certain Cancers: Higher BMI is linked to increased risk of breast, colon, kidney, and liver cancers
- •Fatty Liver Disease: Excess weight can lead to fat accumulation in the liver
- •Mental Health: Weight stigma and body image concerns can contribute to depression and anxiety
Conversely, maintaining a BMI within the normal range is associated with the lowest risk of these conditions and generally better health outcomes.
BMI for Different Populations
The standard BMI categories may not apply equally to all populations. Here are important considerations:
Asian Populations
The WHO recommends lower BMI cut-offs for Asian populations. An Asian person may face increased health risks at a BMI of 23 or above, compared to 25 for Western populations. Many Asian health organizations use 23 as the overweight threshold and 27.5 as the obese threshold.
Children and Adolescents
BMI for children and teens is calculated differently — it uses age- and gender-specific percentile charts (BMI-for-age) rather than fixed categories. A child's BMI is compared to others of the same age and sex. Use our dedicated calculators: BMI Calculator for Children (US) and BMI Calculator for Children (Europe).
Older Adults (65+)
Slightly higher BMI (25-27) may be protective in older adults. This is because some extra weight can help prevent bone loss and provide energy reserves during illness. Very low BMI in elderly individuals is associated with increased mortality risk.
Athletes and Muscular Individuals
BMI can overestimate body fat in athletes and bodybuilders because muscle is denser than fat. A muscular person may have a BMI in the "overweight" or "obese" range while having very low body fat. For these individuals, body fat percentage is a more accurate measure.
Pregnant Women
BMI is not meaningful during pregnancy because weight gain is expected and healthy. Pre-pregnancy BMI is used to determine appropriate weight gain guidelines during pregnancy.
How to Improve Your BMI
Whether your BMI is below or above the healthy range, here are evidence-based strategies to move toward a healthier weight:
If Your BMI is Too High (Overweight/Obese)
- ✓Create a moderate calorie deficit: Reduce intake by 300-500 calories per day for gradual, sustainable weight loss of 0.5-1 lb per week
- ✓Eat more whole foods: Focus on vegetables, fruits, lean proteins, whole grains, and healthy fats. These foods are more filling and nutrient-dense
- ✓Exercise regularly: Aim for 150+ minutes of moderate-intensity activity per week (brisk walking, cycling, swimming) plus 2 days of strength training
- ✓Get enough sleep: Poor sleep disrupts hunger hormones and increases cravings for high-calorie foods
- ✓Manage stress: Chronic stress raises cortisol levels, which promotes fat storage especially around the belly
If Your BMI is Too Low (Underweight)
- ✓Increase calorie intake: Add 300-500 extra calories per day from nutritious foods
- ✓Eat more frequently: Have 5-6 smaller meals throughout the day instead of 3 large ones
- ✓Strength train: Resistance exercises help build muscle mass, which increases healthy weight
- ✓Consult a professional: If unexplained weight loss occurs, see a doctor to rule out underlying conditions
Common BMI Myths Debunked
Myth: "BMI is completely accurate"
BMI is a screening tool, not a diagnostic test. It does not measure body fat directly and has limitations for certain groups (athletes, elderly, different ethnicities). Use it alongside other assessments.
Myth: "BMI applies equally to everyone"
BMI was developed based on data from white European populations. It may not accurately reflect health risk for Asian, African, or other ethnic groups. Different populations may need different BMI thresholds.
Myth: "A high BMI always means poor health"
Some people with high BMI are metabolically healthy, especially if they are muscular or carry weight in their hips and thighs rather than around the waist. Waist-to-height ratio provides additional context.
Myth: "BMI is the only measure that matters"
Health is complex. Blood pressure, blood sugar, cholesterol, waist circumference, fitness level, sleep quality, and mental health all contribute to overall well-being. BMI is just one piece of the puzzle.
Related Health Calculators
For a complete health assessment, combine your BMI with these related tools:
Last reviewed: July 16, 2026
Medical Disclaimer: This calculator is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician or qualified health provider with any questions regarding your health.