GLP-1 BMI calculator: Are you eligible for weight loss treatment?

Most people arrive at a BMI calculator having already done the sum in their head, twice, hoping the number lands on the right side of a line.

That worry is common and understandable.

Nobody enjoys the feeling that their access to treatment depends on a single figure.

Here is what usually happens. People calculate a BMI of 28 or 29, assume they will be turned down, and are surprised to learn that a weight-related health condition brings them comfortably inside the licence.

Others come in at 31 or 32, assume it is a formality, and are surprised that the prescriber wants to talk about their gallbladder history first.

So the BMI matters, but not on its own.

If GLP-1 medications are new to you altogether, our complete UK guide to GLP-1 medications covers the basics before you get to the eligibility question.

Before you begin: A little bit about OnlineClinic

OnlineClinic has been operating since 2011 and has treated more than 2.1 million patients.

The pharmacy is registered with the General Pharmaceutical Council (GPhC), our prescribers are registered with the General Medical Council (GMC), and the service is regulated by the Care Quality Commission (CQC).

As of August 2026, on Trustpilot, the service rating is 4.6 out of 5 based on 6,643 reviews.

One thing to be clear about up front. This guide is for adults aged 18 and over. Weight loss medication is not licensed for minors, and we do not sell these medicines to minors at OnlineClinic.

BMI (body mass index) compares your weight against your height. The calculation is your weight in kilograms divided by your height in metres squared.

If you would rather do it by hand, the formula looks like this.

Someone who is 1.70m tall and weighs 88kg works out as 88 divided by (1.70 x 1.70), which is 88 divided by 2.89, giving a BMI of 30.4.

NICE sets out the standard categories for adults in its guideline on overweight and obesity management, NG246.

This is the licensed criteria for weight loss treatments available in the UK.

Two points worth adding to that table.

• Wegovy has a second, separate licence. Since July 2024, Wegovy has been authorised in the UK to reduce the risk of heart attack and stroke in adults with established cardiovascular disease and a BMI of 27 or above, and NICE recommended it for that purpose in April 2026.

  It is the only GLP-1 medication with that recommendation in the UK.

  If you have had a heart attack or stroke, this is worth discussing with your prescriber.

• The Wegovy pill is new. The MHRA approved oral semaglutide on 11 June 2026, the first GLP-1 tablet licensed for weight management in the UK.

  The BMI criteria are the same as the injection.

  The practical differences are in how you take it rather than in who qualifies. To know more, you can check out our complete guide on the Wegovy pill.

This is the question we are asked most often, usually by someone who suspects they have a qualifying condition but has never heard it described as one.

The conditions that typically count with a BMI of 27 include:

• Type 2 diabetes
• Prediabetes
• High blood pressure (hypertension)
• High cholesterol or raised triglycerides
• Obstructive sleep apnoea
• Non-alcoholic fatty liver disease
• Polycystic ovary syndrome (PCOS)
• Osteoarthritis, particularly in the knees or hips
• Established cardiovascular disease, including a previous heart attack or stroke

A few things people commonly get wrong here.

You do not need a formal diagnosis letter in hand, but the prescriber does need something more than a suspicion.

A blood pressure reading from your pharmacy, a recent blood test result, or a note in your GP record all count.

Prediabetes is most often overlooked, partly because it rarely comes with symptoms.

If a blood test has ever put your HbA1c in the 42 to 47 range, that is relevant, and our guide on Mounjaro for prediabetes goes into what the NICE guidance says about taking the weight loss medicine with prediabetes.

Snoring is not sleep apnoea, though it can be a sign of it.

If your partner has mentioned that you stop breathing in your sleep, that is worth investigating in its own right, separately from any weight loss treatment.

BMI has one great virtue, which is that anyone can calculate it with a tape measure and a set of scales.

It also has a well-known weakness.

It cannot tell the difference between fat and muscle, and it says nothing about where on your body the weight sits.

This matters more than a technicality, because abdominal fat carries most of the cardiometabolic risk.

But there are different ways to measure your BMI accurately, including:

Waist-to-height ratio

NICE now advises using this alongside BMI for anyone with a BMI below 35.

The rule of thumb is easy to remember: Your waist should be less than half your height. The bands are:

• 0.4 to 0.49, healthy central adiposity
• 0.5 to 0.59, increased health risk
• 0.6 or above, further increased health risk

To measure your waist, find the bottom of your ribs and the top of your hips, then wrap the tape around the midpoint between the two, over bare skin or light clothing.

High muscle mass

NICE advises interpreting BMI with caution in people who carry a lot of muscle, because BMI overstates their risk.

A rugby player at BMI 31 is not in the same clinical position as someone else at BMI 31.

Age 65 and over

BMI is also interpreted with more caution in this group, taking comorbidities and functional capacity into account, since a slightly higher BMI may be protective in later life.

The wider shift in how obesity is defined

In January 2025, a report published in The Lancet Diabetes & Endocrinology proposed distinguishing "clinical obesity", where excess body fat is already affecting how organs or tissues function, from "preclinical obesity", where the excess fat is a risk factor but has not yet caused measurable harm.

The Commission recommended confirming excess body fat with at least one measure in addition to BMI, and it has been endorsed by more than 75 medical organisations.

UK licensing still runs on BMI thresholds, so the numbers in this guide are the ones that apply today.

But obesity medicine is moving towards a fuller picture than a single figure, which is roughly how a careful prescriber has always worked anyway.

A prescriber cannot simply take your word for your BMI.

In February 2025, the GPhC added weight-management medicines to its list of high-risk medicines, and the rules that came with that are specific: An online questionnaire on its own is not enough.

Before prescribing, the prescriber must independently verify your weight, height, or BMI, either through two-way communication with you, by accessing your clinical records, or by contacting your GP or regular prescriber.

What BMI verification looks like with us:

• A short two-way exchange with the prescriber through your account
• Your consent to check or confirm details with your GP, where that is the sensible route
• Clear questions about your medical history, current medications, and any conditions or allergies
• A documented record of the decision, including the reasoning if treatment is not issued

Some things rule out GLP-1 treatment regardless of where your BMI lands.

You are not eligible for GLP-1 treatment if you:

• Are pregnant, trying to conceive, or breastfeeding
• Have a personal or family history of medullary thyroid carcinoma, a rare thyroid cancer
• Have Multiple Endocrine Neoplasia syndrome type 2
• Have had a serious allergic reaction to the active ingredient
• Are under 18

Discuss with a prescriber first if you have:

• A history of pancreatitis or gallbladder disease
• Severe kidney or liver problems
• Diabetic retinopathy
• A history of an eating disorder
• Other diabetes medication, particularly insulin or a sulphonylurea
• A planned pregnancy in the next few months

On pregnancy, the MHRA issued specific advice in June 2025. GLP-1 medicines should not be used in pregnancy, just before trying to conceive, or while breastfeeding, because there is not enough safety data.

Anyone who could become pregnant should use effective contraception during treatment, and with some of these medicines, that means stopping up to two months before trying to conceive.

There is an additional point for Mounjaro, which may reduce the effectiveness of oral contraceptives in people who are overweight.

The advice there is to add a non-oral method for four weeks after starting and after each dose increase. We cover this in more detail in Mounjaro and contraception.

On 29 January 2026, the MHRA updated the product information for GLP-1 medicines and issued a safety alert about acute pancreatitis, which is an infrequent side effect but can be serious.

If you have severe, persistent stomach pain, often spreading to the back and sometimes with nausea and vomiting, stop and seek medical advice the same day.

If your BMI is under 27, or between 27 and 30 without a weight-related condition, GLP-1 medication is not licensed for you at the moment.

What is worth doing instead:

• Check your waist-to-height ratio. If it is 0.5 or above, that is a genuine finding to take to a GP, and it may prompt a cardiometabolic risk assessment even at a lower BMI.
• Ask about the conditions you might already have. Blood pressure and HbA1c are quick to check and are the two that most often move someone from ineligible to eligible.
• Look at Xenical if your BMI is 28 or above with risk factors. Orlistat works differently, by reducing how much dietary fat you absorb, and produces more modest average weight loss than the GLP-1 injections. For some people, it is the right fit.
• Re-check your BMI in a few months. BMI is not fixed, and neither is your health history.

Our process is straightforward. From start to finish, this is what happens when you order with us:

1. Fill in the medical questionnaire. It takes 5 to 10 minutes. The questions are thorough on purpose
2. A GMC-registered prescriber reviews your answers. If they need more details or want confirmation from the clinician managing your heart, they will message you through your account
3. If treatment is approved, it is dispensed and dispatched. Next-day delivery, with needles, a sharps bin, and the full patient information leaflet included. Wegovy pens are stable below 30°C and ship in standard insulated packaging
4. If it is not approved, the prescriber explains why. You are not charged for treatment that is not issued

Our Wegovy prices start at £139.99, and every price includes the prescription, the consultation, the packaging, and delivery. There are no hidden fees.

We prescribe Mounjaro for weight management following an online consultation.