BMI calculator
Calculate your body mass index
Enter your height and weight below. BMI is a screening number, not a diagnosis — this page also explains what a clinician reads into it, and what it misses.
Enter your height and weight
BMI does not distinguish muscle from fat and is less reliable for very muscular people, for some ethnic groups, during pregnancy, and at the extremes of height. A clinician interprets it alongside everything else.
What BMI actually measures
Body mass index divides your weight in kilograms by the square of your height in metres. That is all it is: a ratio. It says nothing about how much of your weight is muscle, where fat sits on your body, or how healthy you are — which is why it is a starting point for a conversation rather than a verdict.
It was designed to describe populations, not individuals. Clinicians use it because it is quick and reproducible, then look past it.
What the categories mean
These are the WHO bands the calculator uses. Each boundary belongs to the higher category — a BMI of exactly 25.0 is in the overweight range.
| BMI range | Category |
|---|---|
| Below 18.5 | Below the healthy weight range |
| 18.5 – 24.9 | Healthy weight range |
| 25.0 – 29.9 | Overweight range |
| 30.0 – 34.9 | Obesity, class I |
| 35.0 – 39.9 | Obesity, class II |
| 40.0 and above | Obesity, class III |
Where BMI gets it wrong
- It counts muscle as if it were fat, so it overstates risk for very muscular people
- It ignores where fat is stored, though abdominal fat carries more metabolic risk than fat elsewhere
- Risk thresholds differ between ethnic groups; some guidelines use lower cut-offs for people of South Asian descent
- It is less reliable in older adults, who tend to lose muscle and gain fat at the same BMI
- It is not meaningful during pregnancy
- It skews high for very tall people and low for very short people
BMI for women and for men
The WHO categories are identical for both sexes — there is no separate women's or men's BMI scale. What differs is what the same number implies about body composition, and that is where BMI is weakest.
Women
At an identical BMI, women typically carry a higher proportion of body fat than men. So BMI tends to read as reassuring for a woman with low muscle mass, and the number alone can miss meaningful adiposity. Fat distribution also shifts around menopause, moving from hips and thighs toward the abdomen, without the BMI necessarily changing at all.
Men
Men carry proportionally more muscle at the same BMI, so the number tends to overstate fat for muscular men — a well-trained man can land in the overweight or obesity range on BMI alone. Men also store fat abdominally more readily, which is the pattern most strongly linked to metabolic risk.
Waist measurement is where sex genuinely matters
Unlike BMI, waist circumference thresholds do differ by sex. Measure around the waist at the midpoint between the lowest rib and the top of the hip bone, after breathing out normally.
| Group | Waist measurement | What it indicates |
|---|---|---|
| Women | 80 cm or more | Increased risk |
| Women | 88 cm or more | Substantially increased risk |
| Men | 94 cm or more | Increased risk |
| Men | 102 cm or more | Substantially increased risk |
Thresholds as used by WHO and NICE for waist circumference and health risk.
Taken together, BMI and waist measurement say more than either alone. Someone with a BMI in the overweight range and a normal waist is in a different position from someone with the same BMI and a raised waist.
Neither scale is a diagnosis. A clinician reads them alongside your blood pressure, blood results, medical history and what you are actually trying to change.
How BMI relates to treatment
Most clinical guidelines consider weight-management medication from a BMI of 30, or from 27 when there is also a weight-related condition such as type 2 diabetes, high blood pressure, obstructive sleep apnoea or fatty liver disease. Thresholds differ between guidelines and countries.
Being above a threshold does not mean treatment is appropriate for you, and being below one does not mean nothing can help. A licensed doctor decides, after reviewing your full medical history — and a responsible service will tell you no when that is the honest answer.
If you want a clinical view of your result
The Docalo eligibility assessment is free and takes about ten minutes. A licensed doctor reviews it and decides whether treatment is clinically appropriate. If the answer is no, you are told why and you are not charged.
Free assessment. Membership starts only after a clinician reviews your case.