Anorexic BMI Calculator

Calculate BMI and see where it falls against WHO categories and a historical low-weight reference used in past eating-disorder diagnostic criteria.

⏱ Updated: 18 Sep 2026

Calculator

Anorexic BMI calculator: check where a BMI falls against WHO weight categories and the historical low-weight reference figure once used in eating-disorder diagnostic criteria.

BMI
18.0
Underweight
This BMI is at or below 17.5 — the specific figure once used as one numeric criterion for low body weight in DSM-III-R and DSM-IV diagnostic criteria for anorexia nervosa. Current DSM-5 criteria no longer use a fixed BMI cutoff. This is informational only and cannot diagnose an eating disorder.
WHO classification: Underweight <18.5 · Normal weight 18.5–24.9 · Overweight 25–29.9 · Obese ≥30.

Enter your height and weight in metric or US units to calculate BMI and see where it falls relative to a historically used low-weight reference.

How to Use the Anorexic BMI Calculator

Toggle between Metric and US units first, then enter height and weight — the calculator updates BMI immediately, and if the result lands at or below 17.5 you'll see an additional note explaining that figure's history.

This calculator runs the exact same arithmetic as the site's BMI Calculator. What's different is the second number it checks the result against: 17.5, a figure that spent decades inside the formal clinical definition of anorexia nervosa.

Where 17.5 Came From

The American Psychiatric Association's DSM-III-R, published in 1987, listed body weight "less than 85% of that expected" as one diagnostic criterion for anorexia nervosa — a threshold clinicians commonly translated into a BMI equivalent of roughly 17.5 for adults. DSM-IV, released in 1994, carried forward a version of the same numeric approach. For close to three decades, a single number on a scale factored directly into whether a patient met the formal diagnostic bar.

Why the DSM Dropped the Number

DSM-5, published in 2013, removed the fixed BMI cutoff entirely. In its place: a judgment call on whether body weight is "significantly low" given a person's age, sex, developmental trajectory, and physical health. The reasoning held up under scrutiny. BMI alone was proving both too blunt and too easy to satisfy technically while missing the point — a person can carry a normal or even elevated BMI and still have a serious, life-threatening eating disorder, since restrictive behaviors, purging, and binge patterns don't reliably show up on a scale. A low BMI, meanwhile, has plenty of causes that have nothing to do with disordered eating: illness, genetics, a demanding endurance-training block. A number this replaceable by context didn't belong as a hard line in a diagnostic manual.

This calculator still shows where 17.5 sits, because the history is genuinely informative — it explains why so many older articles, forum threads, and outdated clinical materials still cite that exact figure. But treat it as a historical marker, not an active diagnostic threshold.

BMI = kg ÷ m²
BMI = (lb ÷ in²) × 703

Same formula, same WHO bands as the site's main BMI Calculator: under 18.5 is underweight, 18.5–24.9 is normal, 25.0–29.9 is overweight, 30 and up is obese. The 17.5 marker sits inside the underweight band, toward its lower end.

If you're looking at this number because you're worried about yourself or someone you care about, the real answer doesn't live in the number. Eating disorders are diagnosed through a clinical evaluation that weighs eating patterns, physical symptoms, mental health history, and lab work — not a single ratio typed into a web form. A doctor, a therapist, or an eating-disorder-focused helpline in your country is a far better next step than refreshing this calculator with different numbers.

This tool cannot diagnose an eating disorder, and a low BMI is not itself a diagnosis. If you're concerned about your own relationship with food or a loved one's, please reach out to a doctor, a mental health professional, or an eating-disorder support organization in your country — they can help in ways a calculator never will.