Anorexic BMI Calculator
- Category
- Healthy weight range
- Assessment
- Your calculated BMI does not suggest anorexia nervosa.
- Healthy BMI range
- 18.5 - 25 kg/m²
This result is not a diagnosis. Low weight is only one possible feature of anorexia, and not all low weight is caused by an eating disorder. Eating disorders can also occur at any body weight. If you are worried about your eating or weight, you are not alone and help is available. In the US, the National Eating Disorders Association (nationaleatingdisorders.org) lists support options, and the ANAD helpline is 1-888-375-7767. In a crisis, call or text 988. Outside the US, contact your doctor or a national eating disorder charity.
This anorexic BMI calculator shows your body mass index and whether it falls in an underweight range, along with where to find support if you are worried about eating.
Anorexia nervosa is a serious eating disorder in which a person restricts food and keeps their body weight lower than is healthy, usually driven by an intense fear of gaining weight and a distorted view of their own body. It has one of the highest death rates of any mental illness, yet with timely treatment many people recover fully.
Body mass index is one of the measurements doctors look at, but it cannot diagnose anorexia on its own. A diagnosis is made by a qualified health professional who considers eating behaviors, thoughts about food and weight, physical health and medical history. This calculator only reports where a BMI falls compared with standard categories. It does not offer weight targets and should never be used to aim for a lower weight.
Formula
BMI = weight (kg) ÷ height (m)² = 703 × weight (lb) ÷ height (in)²
For adults aged 20 and over, the World Health Organization classifies a BMI below 18.5 as underweight and divides it into three grades of thinness. Doctors also use BMI as one way to describe how severe anorexia is, alongside many other signs. For children and teenagers, underweight is defined as a BMI below the 5th percentile for age and sex on growth charts, because healthy BMI changes as young people grow.
| Adult BMI (kg/m²) | WHO category |
|---|---|
| Below 16 | Severe thinness |
| 16 – 16.9 | Moderate thinness |
| 17 – 18.4 | Mild thinness |
| 18.5 – 24.9 | Normal (healthy) range |
Weight is only part of the picture. Behavioral and emotional changes often appear first, and people with atypical anorexia can have all the features of the illness while their weight remains in or above the normal range. Possible warning signs include:
- Dramatic weight loss, or failing to gain expected weight during growth
- Strict dieting, skipping meals or cutting out whole food groups
- Preoccupation with calories, weight, body shape or food rules
- Intense fear of gaining weight, frequent weighing or body checking
- Excessive exercise, even when ill, injured or exhausted
- Avoiding eating with others or hiding food
- Missed periods, dizziness, feeling cold, fatigue or fine body hair
- Withdrawal from friends, low mood, anxiety or irritability
Starvation affects nearly every organ. It can slow the heart rate and lower blood pressure, cause dangerous heart rhythm problems and electrolyte imbalances, weaken bones and lead to osteoporosis, stop menstrual periods, and cause muscle loss, anemia, kidney problems and digestive issues. Many of these effects improve with nutritional recovery, which is why early help matters. Refeeding after severe weight loss should be medically supervised because sudden shifts in minerals can be dangerous.
If you recognize these signs in yourself or someone you care about, reaching out is a strong first step. A primary care doctor can check physical health and refer you to specialists such as eating disorder therapists and dietitians. Treatment usually combines nutritional support, psychological therapy and medical monitoring; for young people, family-based treatment has strong evidence. These organizations offer information and support:
- National Eating Disorders Association (NEDA): nationaleatingdisorders.org
- ANAD (National Association of Anorexia Nervosa and Associated Disorders) helpline: 1-888-375-7767
- 988 Suicide & Crisis Lifeline (US): call or text 988 in a crisis
- UK: Beat, beateatingdisorders.org.uk
- Outside these countries: your doctor, or your national health service's mental health line
Frequently asked questions
What BMI is considered anorexic?
There is no BMI that alone means anorexia. Adults with a BMI under 18.5 are underweight, and doctors use lower BMI levels as one way to describe severity, but diagnosis depends on behaviors and thoughts as well as weight.
Can you have anorexia at a normal weight?
Yes. Atypical anorexia has the same restrictive behaviors and health risks while weight stays in or above the normal range.
Does this calculator work for teenagers?
It shows the BMI number, but people under 20 need a BMI-for-age percentile from a doctor. Below the 5th percentile is underweight.
Where can I get help for an eating disorder?
Start with a doctor you trust. In the US, NEDA (nationaleatingdisorders.org) lists resources and the ANAD helpline is 1-888-375-7767; in a crisis call or text 988.
Results are estimates for educational purposes and are not medical advice. Talk to a doctor or other qualified health professional about your situation.
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