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Health calculator

Low BMI Calculator

Calculate BMI and underweight screening context. If this topic feels personally urgent, seek qualified medical or mental-health support.

BMI is a screening number, not an eating-disorder diagnosis. Very low BMI or rapid weight loss warrants professional care.

Method

BMI is weight in kilograms divided by height in meters squared. Adult underweight begins below 18.5 in common CDC/WHO-style screening categories.

Example

At 170 cm and 50 kg, BMI is 50 / 1.70^2 = about 17.3. That is below the common adult underweight screening threshold, but it is not a diagnosis.

Common mistakes

Do not use BMI alone to judge an eating disorder, health status or recovery target. Rapid weight loss, symptoms and mental-health context matter even when BMI is not very low.

Limitations

This page avoids diagnosing anorexia or any eating disorder. Eating disorders can occur at any body size and require professional assessment.

References

Last reviewed: 2026-05-17

Before relying on this result

Use this calculator together with the formula, assumptions, limitations and examples on the page. If the topic involves health, tax, lending, investment, legal, safety or current-rate decisions, treat the number as an estimate and check the relevant primary source or professional guidance.

Calculator metadata last reviewed: 2026-05-14.