Using a BMI calculator for Wegovy: what the numbers mean and what happens next

What NICE's guidance actually says about the Wegovy BMI threshold

NICE's TA875 appraisal, published in March 2023, recommends semaglutide (Wegovy) within NHS specialist weight management services for adults who meet one of two BMI criteria. The first is a BMI of 35 or above with at least one weight-related comorbidity; the second covers BMI 30–34.9 if the person meets specialist-referral criteria. On the private licensed route (which follows the medicine's own Summary of Product Characteristics rather than the narrower NHS commissioning criteria) the thresholds are lower: BMI 30 or above, or BMI 27–29.9 alongside a qualifying health condition. The conditions that count include type 2 diabetes, prediabetes, high blood pressure, raised cholesterol, obstructive sleep apnoea and certain cardiovascular conditions.

That distinction between NHS and private eligibility trips people up regularly. Checking a BMI figure against the Wegovy criteria on an NHS-focused page can give the impression you don't qualify when you may on a private route, or vice versa. The NHS BMI calculator is the right tool to get your number; interpreting what that number means for Wegovy requires knowing which route you're on.

One more thing the calculator cannot do: it doesn't know whether you're pregnant, breastfeeding or trying to conceive. Wegovy is not recommended in any of those situations regardless of BMI. Nor does it account for medicines that interact with semaglutide. These are the questions that belong to a prescriber, not a calculator.

The ethnic-background adjustment, why your qualifying BMI might be lower than the standard figure

Standard BMI cut-offs were developed largely from data on white European populations and don't map as cleanly onto metabolic risk in other groups. UK guidance therefore applies a 2.5 kg/m² downward adjustment for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background. In practice, this means a qualifying BMI of 27.5 (instead of 30) for the primary threshold, or 24.5 (instead of 27) with a weight-related comorbidity.

This adjustment applies to both the licensed private criteria and the NICE NHS thresholds. It's worth checking before assuming you don't qualify. Our page on the BMI needed to take Wegovy covers the adjustment in more detail, including how it interacts with the comorbidity requirement.

A few specific BMI figures come up a lot in the searches people run before considering treatment. A BMI of 25 sits below the standard private threshold but may qualify under the ethnic-background adjustment with a relevant health condition. A BMI of 30 meets the primary licensed threshold outright. A BMI of 26 falls into the territory where a comorbidity and ethnic-background factors become the deciding variables. None of these are yes/no answers without clinical context.

From BMI figure to actual prescription: what the gap looks like

Let's say your BMI is 31. The number clears the primary licensed threshold. That means Wegovy may be clinically appropriate, it does not mean a prescription follows automatically. A prescriber reviewing your case will also look at your medical history, any conditions that rule out GLP-1 medicines (a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2, for example), what you're currently taking, and whether the benefit-risk balance makes sense for you specifically.

This is also where the STEP 1 trial's findings become relevant in a practical way. In that 68-week study, adults with obesity using semaglutide 2.4mg alongside lifestyle changes achieved an average weight reduction of around 15%, compared with around 2.4% on placebo, a result published in the New England Journal of Medicine. Those averages come from a population with a specific clinical profile; whether that profile matches yours is a clinical judgement, not a calculator output.

For context on cost, our weight-loss treatment overview covers what private treatment typically involves financially. The consultation itself at nume is free, and treatment pricing is shown on the treatment page rather than buried in body copy.

How to check your eligibility properly

A BMI calculator is the right first step. Use the NHS tool, note your figure, and then consider whether you have any of the weight-related health conditions that open the lower threshold. If your BMI is 27–29.9, that comorbidity question matters a great deal. If you're unsure whether a condition counts, that uncertainty is exactly what the consultation is for.

At nume, every consultation is read by a GPhC-registered Independent Prescriber (a real clinician, not a questionnaire-scoring system) on the day it's submitted. You'll go through identity verification and live weight confirmation before any prescription is issued. If you're approved, treatment is dispatched the same day for free next-working-day delivery via DPD, arriving in plain, unbranded packaging. Some people keep the pen in the fridge door and barely think about it once it's part of their week; that routine starts with getting the eligibility question answered properly.

Our full Wegovy overview covers the medicine itself in more detail. If you want to understand where to get it, the guide to accessing Wegovy in the UK explains the options, including what to look for in a regulated online pharmacy.