Anorexic BMI Calculator
Check your BMI against underweight and clinical reference bands used in eating-disorder screening, with a plain-language result.
BMI alone cannot diagnose an eating disorder. If you or someone you know is struggling with food or weight, please speak to a doctor or counsellor.
Your BMI
16.5
Below the WHO underweight threshold of 18.5
Clinical reference band
Moderate (BMI 16–17)
ICD-10 bands — reference only
Healthy weight range
50.4–67.8 kg
WHO BMI 18.5–24.9 for your height
The bands shown follow the ICD-10 BMI ranges used as one reference in eating-disorder assessment. A diagnosis requires a full clinical evaluation — never self-diagnose from a number.
Last updated: March 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Use the anorexic BMI calculator to understand where a low weight sits relative to standard reference bands — whether you are studying nutrition or psychology, preparing a health check discussion, or concerned about your own weight and wanting a structured first look. The tool deliberately separates the bare BMI from the clinical band and reminds you that a number alone is never a diagnosis. It is most valuable as a gateway to care: seeing a clearly low BMI in black and white often prompts the conversation with a doctor or counsellor that leads to help. The healthy weight range for your height gives a gentle reference for what restoration might look like. Use it with care and kindness — the aim is awareness, never self-judgement.
How to Use This Calculator
- Step 1: Enter your height in centimetres to compute the BMI basis.
- Step 2: Enter your weight in kilograms along with the height.
- Step 3: Read your BMI and whether it falls below the WHO underweight threshold of 18.5.
- Step 4: If below, check the clinical reference band shown and the healthy weight range for your height.
Worked Example
At 165 cm and 45 kg, the BMI is 16.5, which is below the WHO underweight threshold of 18.5. The calculator places this in the 'moderate' clinical reference band (BMI 16–17) used in eating-disorder assessment, and shows the healthy range for the same height as 50.4–67.8 kg. A 160 cm person at 38 kg has a BMI of 14.8, falling in the 'very severe' band. By contrast, 55 kg at 170 cm gives a BMI of 19 — above the threshold, so no band applies. These are simple BMI calculations with the ICD-10 banding applied.
Tips and Common Mistakes
- •Tip 1: If you are concerned about yourself or someone you know, talk to a doctor or counsellor — early help works best.
- •Tip 2: Treat the band shown as one reference among many; a diagnosis requires far more than a BMI.
- •Tip 3: For loved ones, focus on support and professional care rather than numbers or food shaming.
- ✗Mistake 1: Self-diagnosing an eating disorder from this number — many conditions cause low BMI, and only a clinical assessment decides.
- ✗Mistake 2: Dismissing a low BMI because 'it's just a number' — sustained low weight always deserves a medical check.
Frequently Asked Questions
What does the BMI band in this calculator mean?
It shows where your BMI falls relative to the ICD-10 reference bands used in eating-disorder assessment: mild (17–18.5), moderate (16–17), severe (15–16) and very severe (under 15). These are reference ranges, not diagnoses.
Can a low BMI alone mean I have anorexia?
No. Low body weight has many causes — other illnesses, genetics, thyroid problems or intentional dieting. An eating-disorder diagnosis requires a full clinical assessment of behaviour, thoughts and physical health.
What should I do if my BMI is below 18.5?
See a doctor or qualified nutrition professional to find out why and plan safe weight restoration. If you are restricting food or feeling afraid of gaining weight, speak to a doctor or counsellor — help works best early.
Is the healthy weight range shown the same for everyone?
It is the WHO band (BMI 18.5–24.9) for your height. Individual healthy weights vary with frame, age and muscle, but the band is a reasonable reference for most adults.
How quickly is weight restoration done?
Safely, and under supervision — usually gradually, because rapid refeeding after severe restriction carries medical risks. There is no single timetable; a care team plans it around your health and nutrition status.
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