What This Calculator Does

This tool computes Body Mass Index and places it on the severity scale that DSM-5 uses to grade anorexia nervosa in adults. BMI is weight in kilograms divided by height in metres squared. The severity tiers are Mild at 17 and above, Moderate from 16 to 16.99, Severe from 15 to 15.99, and Extreme below 15. Alongside the score, the calculator reports a weight-restoration target — the weight corresponding to your chosen goal BMI — and the shortfall between current and target weight. The shortfall is floored at zero, so this calculator can never display a weight-loss figure regardless of what is entered.

BMI Grades Severity, It Does Not Diagnose

Anorexia nervosa is a psychiatric disorder defined by restriction of energy intake, intense fear of weight gain, and disturbance in how body weight or shape is experienced. BMI measures the physical consequence of starvation once a diagnosis exists; it plays no part in making one. This distinction matters because atypical anorexia nervosa — meeting every criterion except the low weight — occurs at normal and high BMI and carries the same medical and psychological risk, including bradycardia, electrolyte disturbance, bone loss and suicidality. A reassuring number on this page rules out nothing.

Choosing a Restoration Target

A BMI of 18.5 is the World Health Organization's lower bound for the healthy range and the usual minimum goal. Many eating-disorder services set a higher target, commonly 19 or 20, because menstrual function, bone mineral density and cognitive recovery frequently do not return at the bare minimum. The advanced options let you model all three so the arithmetic reflects the goal your clinician has actually set. The calculator also estimates how long restoration would take at a supervised rate of gain, using the conventional figure of roughly 7,700 kcal per kilogram of tissue.

Refeeding Must Be Supervised

The energy and timeline figures here are arithmetic, not a plan. Reintroducing nutrition after prolonged starvation can trigger refeeding syndrome — a rapid shift in phosphate, potassium and magnesium that can be fatal — which is why restoration is started cautiously and monitored with blood tests. Real energy requirements during refeeding also run well above what this simple calculation predicts, because metabolic rate climbs sharply as nutrition is restored. Published rates are roughly 0.5 to 1.4 kg per week inpatient and 0.2 to 0.5 kg per week outpatient, always under medical supervision.

Please Seek Help

This calculator is informational and is not a diagnostic instrument. It cannot assess eating behaviour, body image, medical stability or psychological risk. If you or someone you know is struggling with an eating disorder, please seek professional medical help immediately — eating disorders have among the highest mortality rates of any psychiatric illness, and they respond well to early treatment.