Underweight & Anorexia BMI Range Calculator
The WHO classifies a BMI below 17.5 as one diagnostic criterion for anorexia nervosa.
⚙ Input Values
📊 Results
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What This Means For You
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📐 Formula
💡 Practical Example
Female, 165 cm, 45 kg: BMI = 45 ÷ 1.65² = 16.53. Classification: Severely Underweight (Anorexic range). Must gain at least 45 – 50.3 kg healthy minimum = 5.3 kg.
📖 About Underweight & Anorexia BMI Range Calculator
The WHO classifies a BMI below 17.5 as one diagnostic criterion for anorexia nervosa. This calculator is educational — always consult a healthcare professional.
To use the Underweight & Anorexia BMI Range Calculator, enter your Height, Current Weight, Biological Sex. The calculator instantly computes Current BMI, WHO BMI Classification and more. Results update in real time as you change any input — no submit button needed.
How to Use This Calculator
Enter your Height (e.g. 165 in cm), Current Weight (e.g. 45 in kg), and Biological Sex — select from Female, Male. Results update instantly — no submit button needed. Use metric or imperial units as labeled. For the most accurate result, measure height and weight in the morning without shoes.
The Formula
BMI = Weight (kg) ÷ Height² (m²)
Anorexia threshold: BMI < 17.5 (WHO clinical criterion)
Healthy min weight = 18.5 × Height (m)²
Worked Example
Female, 165 cm, 45 kg: BMI = 45 ÷ 1.65² = 16.
- Classification: Severely Underweight (Anorexic range). Must gain at least 45 – 50.3 kg healthy minimum = 5.3 kg.
Understanding Your Result
WHO classification: Underweight below 18.5 — Normal weight 18.5–24.9 — Overweight 25.0–29.9 — Obese Class I 30.0–34.9 — Obese Class II 35.0–39.9 — Obese Class III 40 and above. BMI does not distinguish fat from muscle: athletes and those with high muscle mass often read overweight on BMI while having healthy body composition. For adults over 65, a BMI of 23–27 is associated with better outcomes than the standard "normal" range. Use waist circumference alongside BMI: above 88 cm (women) or 102 cm (men) indicates elevated metabolic risk regardless of BMI category.
💡 Expert Health Guidance & Clinical Context
- This calculator uses clinically validated formulas and population reference data published by the WHO and NIH. Results are screening estimates, not medical diagnoses.
- Consult a licensed healthcare provider before making any changes to diet, medication, or exercise based on these results — individual variation is significant.
- Genetics, chronic conditions, and concurrent medications can dramatically affect what a "normal" result means for a specific individual.
- Track your results over time: a single data point is less meaningful than a trend measured consistently across multiple weeks or months.
- The CDC recommends adults receive routine health screenings at least annually. Use these calculations to prepare informed questions for your physician.
- Body composition, lifestyle factors, and stress levels all interact with the metrics shown here. No single number captures your full health picture.
- For pediatric or geriatric populations, reference ranges may differ significantly from the adult standards used in general calculators.
- Always cross-reference results with laboratory tests, clinical examinations, and professional medical evaluation before acting on any finding.
Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.