Anorexic BMI Calculator
Enter your height and weight to compute your BMI and check it against the BMI 17.5 underweight/anorexia reference threshold.
Example
Someone who is 170 cm tall and weighs 50 kg:
height = 1.70 m
BMI = 50 / (1.70 x 1.70)
= 50 / 2.89
= 17.3
Below 17.5 threshold? Yes
A BMI of 17.3 falls below the 17.5 reference point and is flagged as underweight for informational purposes.
How it works
BMI is weight in kilograms divided by height in metres squared (kg/m squared). A BMI below 17.5 is commonly cited as a clinical reference point for anorexia; this tool is informational and not a diagnosis.
Good to know
This calculator takes your height and weight, computes your Body Mass Index (BMI), and then shows specifically where that number sits in relation to the BMI 17.5 reference point that has been used clinically as one marker associated with anorexia nervosa. Unlike a generic BMI tool, it adds a clear "below threshold?" flag and breaks the low end of the scale into finer bands, so the focus is on the underweight range rather than the full overweight-to-obese spread.
It is aimed at people who are tracking a low or falling weight, parents or carers keeping an eye on someone, and anyone curious about what the 17.5 figure actually means in numbers. It runs entirely in your browser with both metric (cm/kg) and imperial (ft/in/lb) inputs, so nothing you type is sent or stored anywhere.
To read the result, look at three parts together: the BMI value itself, the category label (which ranges from "Healthy range" down through "Underweight," "Severe underweight," and "Very severe underweight" below 15), and the yes/no threshold flag. A "Yes" means your BMI is under 17.5; it is a flag for context, not a diagnosis. Eating disorders are assessed by behaviour, history, and many other factors, and they occur at every weight, so a "No" does not rule anything out.
- Practical tip: weigh yourself in the morning before eating and measure height without shoes, since day-to-day fluid and clothing differences can swing BMI by a few tenths and push you across a band boundary. If a low or dropping number worries you, treat it as a prompt to talk to a doctor or a trusted person rather than a verdict.
Frequently asked questions
Why is the threshold set at BMI 17.5?
A BMI below 17.5 has historically been used in clinical criteria (such as ICD-10) as one reference marker associated with anorexia nervosa. It is only a guideline, not a diagnosis, since eating disorders are assessed using behaviour, history, and other factors, not BMI alone.
Does a BMI above 17.5 mean I do not have an eating disorder?
No. Eating disorders can occur at any weight or BMI, including healthy and higher ranges. BMI is just one number and cannot rule an eating disorder in or out. If you are concerned about your eating or body image, speak with a healthcare professional.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
What is the BMI range for anorexia?
A BMI below 17.5 has been used in some clinical criteria, such as ICD-10, as one reference marker for anorexia nervosa. It is only a guideline, and diagnosis depends on eating behaviour, medical history, and other factors rather than BMI alone.
How do you calculate BMI from height and weight?
BMI equals weight in kilograms divided by height in metres squared (kg/m squared). For example, 50 kg at 1.70 m is 50 / (1.70 x 1.70) = 50 / 2.89, which is about 17.3.
What is considered severely underweight on the BMI scale?
This tool labels a BMI under 16 as severe underweight and a BMI under 15 as very severe underweight, with the standard underweight cutoff at 18.5. These are informational bands, not clinical diagnoses.
Is a BMI of 17 dangerous?
A BMI of 17 falls in the underweight range and below the 17.5 reference point, but a single number does not determine health risk on its own. Factors such as recent weight change, age, muscle mass, and symptoms matter, so a healthcare professional is the appropriate source for assessment.
Does BMI work the same for teenagers and children?
No. For children and teens, clinicians typically use age- and sex-specific BMI percentiles rather than fixed adult cutoffs like 17.5 or 18.5. An adult BMI calculator may not interpret a young person's measurements correctly.
Can you have anorexia with a normal BMI?
Yes. Eating disorders, including restrictive eating patterns, can occur at a healthy or higher BMI, a situation sometimes described as atypical anorexia. BMI cannot confirm or rule out an eating disorder.
How accurate is BMI as a health measure?
BMI is a quick screening ratio of weight to height and does not distinguish muscle from fat or account for body composition, frame, or distribution of weight. It is useful as a rough indicator but is not a complete picture of health.
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