What the anorexic BMI threshold means
Body Mass Index divides your weight by the square of your height, giving a single number that roughly describes how heavy you are for your stature. A BMI of 17.5 is widely cited as a clinical reference point because it appears among the diagnostic criteria for anorexia nervosa.
This tool reports your BMI, tells you whether it sits below that 17.5 mark, and works out how much weight you would need to gain to reach both 17.5 and 18.5 — the bottom of the conventional normal range.
Reading the comparison
The bar chart lines up your current BMI against the 17.5 anorexic threshold and the 18.5 lower edge of the normal band. Seeing the three side by side makes it clear how far below or above the markers you currently are.
If your BMI is under 17.5, the two weight-gain figures show the kilograms needed to clear each milestone. When you are already above a threshold, that figure is zero.
Important limits of BMI
A single number cannot capture health, and BMI in particular ignores body composition:
- BMI cannot tell muscle from fat, so it misreads very lean or very muscular bodies.
- A low BMI alone is not a diagnosis of an eating disorder.
- Rapid or unexplained weight change matters more than a single reading.
- Children, athletes and older adults need age- and context-specific assessment.
Health disclaimer
This calculator is informational only and is not a medical diagnosis. Disordered eating is a serious condition that involves far more than a number on a scale. If you are worried about your weight, your relationship with food, or someone you care about, please speak with a doctor or a qualified mental-health professional.
Formula
bmi = weightKg / height²; flag if bmi < 17.5 (height in metres)Frequently asked questions
- Is a low BMI alone a diagnosis?
- No. BMI below 17.5 is one marker, but anorexia is diagnosed by a professional based on many factors. Please seek medical advice if concerned.