How BMI is calculated
Body mass index is your weight in kilograms divided by your height in metres squared. A person who weighs 90 kg and stands 1.70 m tall has a BMI of about 31.1. The sum gives the same answer whether the weight is mostly muscle or mostly fat. This is one of its limits.
BMI works well across a population and as one part of a personal assessment. It cannot show where you carry fat, how strong your muscles are, whether you have lost weight without trying or whether you eat enough. A single number does not replace a talk about your symptoms, your history and how weight affects your daily life.
Ethnicity and waist size change the picture
NICE recognises that heart and metabolic risk can start at a lower BMI in some ethnic groups. Clinicians may use adjusted thresholds in those assessments. They should follow the specific guidance and pathway. A correction from a social media post is no substitute.
Waist-to-height ratio adds information about fat around the middle in suitable adults. It is still a screening tool. Pregnancy, body shape, how the tape is used and some medical conditions limit what the result means. Ask your clinician which measurements help in your case and how each one affects the decision.
Eligibility depends on more than one number
A medicine can have licence criteria, NHS funding criteria and a provider's own assessment rules. These layers are related, but they differ. Meeting a BMI threshold does not guarantee a prescription. Falling outside one service's funding pathway does not mean no other clinical help exists.
A consultation should also cover related conditions, other medicines, reasons you should not take the drug, pregnancy plans, eating difficulties and past treatment. Accurate measurements protect this assessment. Online pharmacy guidance requires independent checks. A service should not rely only on numbers you type into a form.
Measure the same way each time
For tracking, use the same method each time and write down the date. If you are unsure of your height, measure again. A fresh reading beats repeating an old guess. Bring past weights if they explain a change, but never alter a measurement to reach a threshold.
If weighing upsets you or links to an eating disorder, tell the clinical team. They may be able to arrange measurements and conversations in a less distressing way. The aim is safe care. A good plan can track energy, strength, blood pressure, glucose or mobility alongside weight, so success means more than one target on a chart.
Close to a threshold
If you sit close to a cut-off, ask how the service handles measurement error. The answer should come from the service's clinical process. Re-measuring until the number crosses a line is not a fair process. A second accurate reading can correct a mistake. Deliberately changing the figures cannot.
If one pathway cannot offer treatment, ask what other support or assessment suits you. Your health needs remain when you miss a funding threshold.
Sources
Your own medicine leaflet and prescriber come first. A source from another country does not mean the same rule applies in the UK.
- NICE NG246: Overweight and obesity management nice.org.uk
- GPhC: Online pharmacy safeguards for medicine supply pharmacyregulation.org
- NHS: Overweight and obesity in adults nhs.uk
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