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BMI Calculator
Get your Body Mass Index instantly: with a visual WHO category gauge, healthy weight range, interactive chart, and a one-click PDF report. Free, works on any device.
BMI Categories and Health Risk
The Body Mass Index scale uses internationally recognised thresholds set by the World Health Organization. Each band carries a different level of associated health risk.
| BMI Range | Category | Health Risk Level |
|---|
| Below 18.5 | Underweight | Nutritional deficiency, bone density loss, reduced immunity |
| 18.5 to 24.9 | Normal Weight | Lowest risk: the target range for most adults |
| 25.0 to 29.9 | Overweight | Raised risk of hypertension and type 2 diabetes |
| 30.0 to 34.9 | Obese Class I | High risk of cardiovascular disease and sleep apnoea |
| 35.0 to 39.9 | Obese Class II | Very high risk, metabolic syndrome, joint deterioration |
| 40.0 and above | Obese Class III | Extreme risk, life-threatening complications likely |
The BMI Formula
BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is now the WHO-endorsed standard for population-level weight screening.
Metric formula
Example: A person who is 1.75 m tall and weighs 70 kg has a BMI of 70 Γ· (1.75 Γ 1.75) = 22.86: Normal Weight.
Imperial formula
Example: A person who is 69 inches tall and weighs 154 lbs has a BMI of [154 Γ· 4,761] Γ 703 = 22.73: Normal Weight.
Important Limitations of BMI
BMI is a quick screening tool, not a complete health assessment. Understanding where it falls short helps you interpret your result correctly:
- Muscle vs. fat: BMI does not distinguish muscle tissue from fat. Professional athletes and bodybuilders are frequently classified as overweight despite very low body fat percentages.
- Age: Older adults carry more body fat at the same BMI than younger people, so health risk at any given BMI value is often higher after 60.
- Ethnicity: South Asian and East Asian populations face elevated metabolic risk at lower BMI values than the standard thresholds suggest. Several health bodies recommend lower cut-off points for these groups.
- Pregnancy: Standard adult BMI is not appropriate during pregnancy. Use pregnancy-specific weight gain guidelines instead.
- Children: For anyone under 18, use age- and sex-specific BMI-for-age percentile charts from the CDC or WHO.
Frequently Asked Questions
What is a healthy BMI for adults?
A BMI between 18.5 and 24.9 is classified as Normal Weight and is associated with the lowest risk of weight-related conditions according to WHO and CDC guidance. That said, a single number does not capture the full complexity of health.
Is BMI the same calculation for men and women?
The formula is identical, but women naturally carry more body fat than men at the same BMI. Some clinicians adjust their interpretation accordingly. Body fat percentage testing provides a more sex-specific result.
How do I interpret BMI for a child?
For anyone under 18, the adult categories do not apply. Use age- and sex-specific BMI-for-age percentile charts from the CDC or WHO growth standards. A result at or above the 95th percentile is classified as obesity in children.
Can I download my BMI result?
Yes. After calculating, click Save PDF for a formatted A4 report or Save Excel for a spreadsheet. Both files are generated entirely inside your browser and are never uploaded to our servers.
My BMI says Overweight but I feel and look healthy: what should I do?
BMI is a starting point, not a diagnosis. If you exercise regularly, have good bloodwork, and maintain a healthy lifestyle, discuss your result with a healthcare professional who can look at the full picture rather than a single number.
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Sources & References
Medical disclaimer: This calculator provides general health information and does not constitute professional medical advice, diagnosis or treatment. Always consult a qualified healthcare provider before making decisions about your health.
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FCALCULATOR Health Team
Last reviewed
This calculator uses the WHO-standard BMI formula. Category definitions are cross-referenced annually with CDC and WHO guidelines to ensure accuracy.