Question 1

What is the BMI Test?

Accepted Answer

The Body Mass Index (BMI) is a number calculated from your weight and height - specifically, weight in kilograms divided by height in metres squared. It’s used worldwide as a quick screening tool to estimate whether your weight is in a healthy range. It does not take body fat into account, but it serves as an initial indicator of the risks associated with abnormal weight.

Question 2

How reliable is BMI?

Accepted Answer

BMI is well validated as a population-level indicator and is used by the WHO, CDC, NHS, and NICE as the first step in weight assessment. It’s less reliable for individuals when body composition or ethnicity differs from the average - for example, athletes with high muscle mass, older adults with low muscle mass, or people of Asian descent who carry more body fat at the same BMI. For these groups, additional measurements (waist circumference, body composition analysis) are recommended.

Question 3

How are results categorised?

Accepted Answer

Results follow the WHO classification: under 18.5 = underweight, 18.5–24.9 = normal, 25.0–29.9 = overweight, 30.0–34.9 = obesity class I, 35.0–39.9 = obesity class II, and 40 or above = obesity class III (severe). The “normal” range is associated with the lowest health risk for most adults; risk rises as BMI moves further from this range in either direction.

Question 4

What does the BMI test ask?

Accepted Answer

Just two numbers: your current weight in kilograms and your height in centimetres. From those, your BMI is calculated automatically and matched to a WHO category. Nothing else is required. We do not collect or store your weight or height - the calculation runs in your browser. We may ask a few quick questions about your health (e.g. heart or hormonal conditions) to provide a more complete result.

Question 5

Is BMI a diagnosis?

Accepted Answer

No. BMI is a screening indicator, not a diagnosis. A BMI in the overweight or obese range does not by itself mean you have a disease; it indicates that a fuller assessment - including waist circumference, body composition, blood pressure, blood sugar, and lipid panel - is worthwhile. A BMI in the normal range does not by itself mean you are metabolically healthy. The right interpretation always comes from a clinical assessment.

Question 6

Where does BMI not apply well?

Accepted Answer

BMI is less reliable for: athletes (high muscle mass can push BMI into the overweight category without elevated health risk); older adults (loss of muscle and bone mass can mask excess body fat at a “normal” BMI); children and adolescents (use age- and sex-specific WHO growth curves instead); pregnant women (use pre-pregnancy BMI plus recommended weight-gain ranges); and people of Asian descent (lower BMI thresholds apply per WHO international guidance).

Question 7

How can I improve my BMI?

Accepted Answer

Sustainable changes work best: a Mediterranean-style eating pattern (vegetables, legumes, fish, olive oil; less added sugar and trans fats), regular physical activity most days of the week, 7–9 hours of sleep, and stress management. If your BMI is outside the normal range, these changes are most effective with personalised guidance from a clinician or/and dietitian - both because individual targets vary and because underlying causes (thyroid, hormonal, metabolic, medication side effects) need to be ruled out.

Question 8

What if my BMI is outside the normal range?

Accepted Answer

A BMI outside 18.5–24.9 is a signal to look closer, not a verdict. A BMI of 30 or above is linked to a higher risk of conditions such as type 2 diabetes, hypertension, dyslipidaemia, coronary heart disease, sleep apnoea, fatty liver disease, certain cancers, osteoarthritis, and infertility. A BMI under 18.5 is linked to anaemia, osteoporosis, hormonal disturbances, vitamin deficiencies, and a weakened immune system. The good news: most of the risk is modifiable, and the earlier you act the easier it is. The right next step is a structured, supervised plan rather than a crash diet.

BMI Calculator | Calculate your Body Mass Index

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