Anorexic BMI Calculator
Check your BMI against the anorexia threshold of 17.5. Free BMI calculator with severely underweight detection, category breakdown, charts, and guidance.
About This Calculator
The Anorexic BMI Calculator helps assess body mass index with a focus on the severely underweight range (BMI below 17.5) used as one diagnostic criterion for anorexia nervosa according to WHO ICD-10 guidelines. While it calculates BMI using the standard formula, it provides additional context by flagging the anorexic threshold and showing detailed category ranges from severely underweight to obese.
BMI is calculated using the formula: BMI = weight (kg) / (height in meters)². For example, a 165 cm person weighing 50 kg has a BMI of 18.4, which is in the underweight range. If the same person weighs 47 kg, their BMI drops to 17.3, falling into the severely underweight (anorexic) range. This calculator provides instant results with visual charts comparing your BMI against all category thresholds.
BMI Categories
- Severely Underweight (Anorexic Range): BMI below 17.5
- Underweight: BMI 17.5 - 18.4
- Normal Weight: BMI 18.5 - 24.9
- Overweight: BMI 25 - 29.9
- Obese: BMI 30 or higher
Important Note
This calculator is a screening tool only. A BMI below 17.5 is one of several diagnostic criteria for anorexia nervosa. A formal diagnosis requires comprehensive evaluation by a healthcare professional including psychological assessment, and should not be based solely on BMI. If you or someone you know has a very low BMI or disordered eating patterns, please seek professional medical help.
Regional Notes
India: The Indian Health Ministry recommends modified BMI thresholds for South Asians: Overweight at BMI 23+ and Obese at BMI 25+. The anorexic threshold of 17.5 remains the same across all populations.
United States: The APA (American Psychiatric Association) defines anorexia nervosa as "restriction of energy intake relative to requirements leading to significantly low body weight" — typically interpreted as BMI below 18.5, with severe cases below 15 requiring hospitalization.
United Kingdom: NICE guidelines recommend specialist eating disorder services for adults with a BMI below 17.5. The NHS uses the same WHO BMI categories for general weight classification.
Frequently Asked Questions
What BMI is considered anorexic?
According to WHO ICD-10 diagnostic criteria, a BMI below 17.5 is used as one indicator for anorexia nervosa. Our calculator flags this threshold specifically while also showing standard WHO BMI categories. A BMI of 17.5 or lower is classified as severely underweight and may indicate an eating disorder requiring medical attention. However, BMI alone is not diagnostic — a healthcare professional must evaluate all clinical criteria.
How is BMI calculated for anorexia assessment?
BMI is calculated using the standard formula: weight (kg) divided by height (m) squared. For example, a person weighing 50 kg with a height of 165 cm would have a BMI of 50 ÷ (1.65 × 1.65) = 18.4, which falls in the underweight category but above the anorexic threshold of 17.5. Our calculator supports both metric units and provides instant BMI calculation with category classification.
What are the BMI categories for underweight?
The underweight BMI category is divided into two sub-ranges: Severely Underweight (Anorexic Range) — BMI less than 17.5, and Mildly Underweight — BMI between 17.5 and 18.4. The standard WHO categories define normal weight as 18.5-24.9, overweight as 25-29.9, and obese as 30 or higher.
Is the anorexic BMI calculator accurate?
The calculator uses the standard WHO BMI formula which is medically validated. For adults aged 18-65, BMI is generally accurate as a screening tool. However, BMI does not account for muscle mass, bone density, body fat distribution, or age-related changes. Athletes, elderly individuals, and pregnant women should use additional assessment methods. Always consult a healthcare provider for proper medical evaluation.
What BMI is dangerously low?
A BMI below 17.5 is considered dangerously low and is associated with increased health risks including osteoporosis, heart problems, fertility issues, weakened immune system, and organ damage. A BMI below 15 is classified as very severely underweight and requires immediate medical intervention. In India, the health ministry recommends using a lower overweight threshold of 23 due to higher metabolic risks in South Asian populations.
How can I gain weight if my BMI is too low?
If your BMI is below 18.5, consider: 1) Eating nutrient-dense foods like nuts, avocados, whole grains, and lean proteins, 2) Eating 5-6 smaller meals throughout the day instead of 3 large ones, 3) Adding healthy fats like olive oil, ghee, and nut butters to meals, 4) Strength training to build muscle mass, 5) Consulting a dietitian or doctor for a personalized plan. If your BMI is below 17.5, seek professional medical help as this may require specialized treatment.
What is the difference between underweight and anorexic BMI?
Being underweight (BMI below 18.5) is a BMI classification that can result from various causes including genetics, illness, or metabolism. Anorexia nervosa is a specific eating disorder characterized by severely low body weight (typically BMI below 17.5), intense fear of gaining weight, and distorted body image. While all anorexic BMIs are underweight, not all underweight individuals have anorexia. A formal diagnosis requires psychological evaluation by a mental health professional.
What BMI requires hospitalization for anorexia?
In medical practice, a BMI below 15 often requires inpatient hospitalization for medical stabilization. A BMI between 15-17.5 may indicate intensive outpatient or residential treatment, depending on the rate of weight loss, vital sign instability, and medical complications. In the UK, NICE guidelines recommend specialist eating disorder services for adults with BMI below 17.5. In the US, the APA guidelines suggest hospitalization when BMI is less than 15 or when weight loss exceeds 1 kg per week.