Free anorexic bmi calculator
This tool checks one thing: whether a body mass index falls below 17.5 — a figure that older diagnostic manuals linked to anorexia. Enter a height and weight and it compares the BMI against that marker. Please read it as a screening signal, not a diagnosis: a number alone cannot tell anyone whether they have an eating disorder, and support is available whatever the result.
On this page14 sections
BMI is a screening tool, not a diagnosis. How accurate is this?
Results are estimates. Consult a professional.
Before you read your number, please read this
This tool checks one thing: whether a body mass index falls below 17.5 — a figure historically linked to anorexia in older diagnostic manuals. It is a screening marker, not a diagnosis. A number on its own cannot tell you, or anyone, whether you have an eating disorder. Anorexia is a serious mental-health condition diagnosed by trained professionals who look at thoughts, feelings, and behaviours around food and body — not at weight alone.
What the anorexic BMI calculator does
The calculator takes your height and weight, works out your body mass index with the standard formula, and compares that figure against the 17.5 marker. If the result falls below 17.5, the tool flags it; if it sits above, it does not. That is the whole of what it measures — a single number against a single line.
It is worth being clear about what the calculator is not doing. It is not assessing whether you eat enough, how you feel about your body, your medical history, or your mental health — the things that actually define an eating disorder. It cannot see any of that. It only sees two numbers you typed in. Please read every result it gives in that light.
What does a BMI below 17.5 mean?
A BMI of 17.5 sits inside the underweight range — the World Health Organization classifies any adult BMI below 18.5 as underweight. The specific figure of 17.5 has a particular history: it was used as a diagnostic cut-off for anorexia nervosa in older clinical manuals, the ICD-10 and the earlier DSM-IV. That is why so many "anorexic BMI" tools, including this one, draw their line there.
Modern diagnosis has moved on. The current manual, the DSM-5, deliberately removed the rigid weight cut-off, because clinicians found that a single number missed too many people who were genuinely unwell. Today a clinician looks at whether someone is at a "significantly low weight" for their own context — alongside their behaviour and psychology — rather than ticking a box at 17.5. So the marker is best understood as a historic flag worth a second look, not a threshold you cross into a diagnosis.
Why BMI cannot diagnose anorexia
Anorexia nervosa is a mental-health condition, not a body-weight category. It is defined by the way a person thinks and behaves around food and their body: a restriction of what they eat, an intense fear of gaining weight, and a self-image that is heavily tied to weight or shape. None of that lives on a scale, and none of it can be captured by a height-and-weight ratio.
- People at any weight can have anorexia. Someone can be deeply unwell — restricting, fearful, distressed — while their BMI still reads in the "normal" range. This is sometimes called atypical anorexia, and it is just as serious.
- A low BMI has many causes. Genetics, a fast metabolism, illness, or simply a smaller natural build can all produce a BMI below 17.5 in people with a perfectly healthy relationship with food.
- The harm is in the behaviour, not the number. Two people with the same BMI can be in entirely different situations — one thriving, one struggling. The difference is invisible to a calculator.
The National Eating Disorders Association is explicit that BMI "has very little usefulness as a measure of any individual's medical status" and should not be used on its own to draw conclusions about a person. Take that to heart: this tool can raise a gentle question, but only a qualified professional can answer it.
A worked example using the anorexic BMI calculator
Here is how the calculator works through a single set of figures — and, just as importantly, how to interpret what it returns. The aim is to understand a screening result, not to chase any particular number.
- Enter the height and weight. Say the figures entered are a height of 1.68 m and a weight of 48 kg. (You can type metric or imperial; the calculator converts for you.)
- Square the height. 1.68 × 1.68 = 2.82.
- Divide weight by that figure. 48 ÷ 2.82 = a BMI of about 17.0.
- Compare it to the 17.5 marker. 17.0 is below 17.5, so the tool flags the result — meaning it sits in the range that older manuals associated with anorexia.
- Read it as a prompt, not a verdict. The right next step is not a target or a plan to change the number; it is to talk to a doctor or a trusted person, who can look at the whole picture the calculator cannot see.
The DSM-5 severity bands (for clinical context)
When a clinician has already diagnosed anorexia nervosa through a full assessment, the DSM-5 offers a set of BMI bands to describe how severe the condition currently is. These bands are a clinical shorthand used after a diagnosis — they are shared here for context and understanding, not as something to measure yourself against.
| DSM-5 severity | Adult BMI |
|---|---|
| Mild | 17 and above |
| Moderate | 16 – 16.99 |
| Severe | 15 – 15.99 |
| Extreme | below 15 |
Source: American Psychiatric Association, DSM-5. These severity bands apply only once anorexia nervosa has been diagnosed by a clinician; severity can also be adjusted for symptoms, distress, and disability.
Note the small but important difference from this tool's marker: the DSM-5 mild band starts at 17.0, whereas the historic diagnostic cut-off many calculators still use is 17.5. The gap is a reminder that these lines are conventions that have shifted over time — useful for professionals, but not precise verdicts about any one person.
Health risks of being severely underweight
Carrying too little weight, however it comes about, puts real strain on the body. When the body does not get enough energy and nutrition over time, it begins to slow down and conserve, and many systems are affected at once. These are reasons to seek care and support, not reasons for alarm or shame.
- Heart. A very low weight can slow the heart rate, lower blood pressure, and disturb heart rhythm.
- Bones. Reduced bone density (osteopenia or osteoporosis) raises the long-term risk of fractures.
- Hormones and fertility. Periods may stop or become irregular, and hormone balance can be disrupted.
- Blood and immunity. Anaemia, a weakened immune response, and low blood sugar become more likely.
- Whole-body effects. Fatigue, feeling cold, hair thinning, and difficulty concentrating are common.
Where to get help and support
If anything on this page resonated with you, please know that help is available and recovery is genuinely possible. You don't have to have a diagnosis — or a particular number — to reach out. A good first step is talking to your GP or doctor, who can listen without judgement and connect you with care. The organisations below also offer information and support:
Sources and further reading
The BMI formula follows the World Health Organization and CDC definitions. The 17.5 figure reflects the historic ICD-10 and DSM-IV diagnostic cut-offs for anorexia nervosa. The severity bands (mild ≥17, moderate 16–16.99, severe 15–15.99, extreme below 15) are from the DSM-5, which removed the rigid weight criterion used in earlier manuals. The cautions about BMI's limits as an individual measure draw on guidance from the National Eating Disorders Association.
American Psychiatric Association — DSM-5 anorexia nervosa criteria and severity specifiers.World Health Organization — adult BMI classification (underweight, below 18.5).National Eating Disorders Association — BMI and eating disorders.Frequently asked questions about the free anorexic bmi calculator
About this anorexic BMI calculator
This calculator runs entirely in your browser. The height and weight you enter never leave your device — nothing is sent to a server, logged, or shared. It computes BMI with the standard WHO formula and compares the result against the historic 17.5 marker, updating instantly. It is a screening tool only, and is not a substitute for advice from a doctor or a qualified eating-disorder professional.
For body mass index in a broader context, see the BMI calculator, the healthy weight calculator, and the ideal weight calculator. If you are worried about your relationship with food or your body, please reach out to a doctor or an eating-disorder support organisation — you do not have to face it alone.