BMI Weight Loss Calculator: Check Injection Eligibility
Use our BMI weight loss calculator to check your body mass index and get an initial indication of eligibility for weight loss medications. A prescriber will assess your medical history and suitability before any treatment is prescribed.
How to use our BMI calculator
- Select whether you are currently taking weight loss medication.
- Choose metric or imperial units, then select your current height and weight.
- Select “Check eligibility” to see your BMI and the calculator's initial indication.
Use accurately measured height and weight. The result is a screening guide, not a diagnosis or a guarantee that treatment will be prescribed.
What should I do after checking my BMI?
To plan your next steps, you can use our calorie deficit calculator to estimate a daily calorie target, or read about weight loss medications and how treatment is assessed.
If Mounjaro is one option you are considering, review its doses, prices and assessment process before you buy Mounjaro online. Your BMI result alone cannot confirm suitability or guarantee a prescription.
If you wish to request treatment, complete the online weight loss consultation. A clinician will review your information and decide whether treatment is suitable before a prescription is issued.
Weight Loss Eligibility Check
Find out if you're eligible for our weight loss treatment in just 30 seconds.
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Your information is secure and confidential
This calculator checks BMI only and cannot confirm medication eligibility. For adults starting Mounjaro or Wegovy for weight management, a BMI of 27 to below 30 must be considered alongside at least one weight-related health condition under the standard licensed criteria. A full clinical assessment is required before treatment can be prescribed or supplied. See the explanation below for starting, switching and maintenance considerations.
BMI for Weight Loss Injections: What Your Result Means
Your result helps a prescriber assess whether you meet the starting BMI criteria for weight loss injections. It does not confirm that a medicine is suitable or guarantee a prescription.
If you are new to treatment, understanding how weight loss injections work can make the eligibility criteria easier to put in context.
For adults starting Mounjaro or Wegovy injections for weight management, the standard licensed BMI criteria are:
| Your starting BMI | What the result means |
|---|---|
| Below 27 | You generally fall below the standard licensed starting BMI criteria. A prescriber can explain whether any different clinical pathway applies. |
| 27 to below 30 | You may meet the BMI criteria if you also have at least one weight-related health condition. |
| 30 or above | You meet the starting BMI criterion, but still need a clinical assessment before treatment can be prescribed. |
Relevant conditions can include high blood pressure, abnormal cholesterol levels, obstructive sleep apnoea or type 2 diabetes. Your prescriber will also review your medical history, current medicines and other factors affecting suitability. These medicines are used alongside a reduced-calorie diet and increased physical activity.
Examples: what your BMI result could mean
- BMI 28 without a weight-related condition: generally does not meet the standard licensed starting criteria.
- BMI 28 with diagnosed high blood pressure: may meet the starting criteria, subject to a clinical assessment.
- BMI 32: meets the starting BMI criterion; a prescriber still needs to confirm that treatment is suitable.
Starting BMI and current BMI are different
If you already take weight-loss medication, your current BMI needs to be considered alongside your original starting BMI, treatment history and response. A lower BMI after losing weight does not, by itself, determine whether treatment should continue. Switching and maintenance decisions require an individual clinical review.
The table describes the standard adult licensed starting criteria. Ethnicity-related risk assessment and Happy Pharmacy's switching and maintenance pathways are explained separately below; they should not be confused with these standard starting thresholds.
What does a BMI of 27 mean?
A BMI of 27 falls within the standard adult overweight range. It is a prescribing threshold used with other criteria, rather than a point at which health risk suddenly begins. BMI also has limitations, including differences in muscle mass and ethnic background.
Read the official Mounjaro prescribing information and Wegovy prescribing information, or see our weight-loss medication guide. To request an assessment, complete the online weight-loss consultation.
Background
A word on the limits of BMI
BMI is a useful starting point but it is not perfect. It does not tell the difference between muscle and fat, so a very muscular person may have a high BMI without carrying excess body fat. It also does not show where fat is stored on the body, and the standard thresholds may need to be adjusted for some ethnic backgrounds. For this reason, your BMI should always be looked at alongside the rest of your medical picture. Understanding why obesity is more than a BMI number helps explain why clinicians also assess your health and how excess body fat affects daily life.
What is BMI and why does it matter?
A simple measure of body size Body Mass Index (BMI) is a number worked out from your height and your weight. It gives a quick estimate of whether your weight sits within a healthy range for someone of your size. BMI was first developed in the nineteenth century and is now used by doctors, nurses, and pharmacists all over the world as a first-line screening tool. Why BMI is important BMI does not measure body fat directly, but it gives a reliable indication, across a population, of how much body fat a person is likely to be carrying. As BMI rises above the healthy range, so does the risk of a number of long-term health conditions, including type 2 diabetes, high blood pressure, heart disease, stroke, certain cancers, and joint problems such as arthritis. For this reason, clinicians use BMI as the first step in deciding whether weight-management treatment is likely to be helpful — and whether a prescription medicine such as Mounjaro (tirzepatide) or Wegovy (semaglutide) may be appropriate. How to calculate your BMI The formula is:BMI = weight (kg) ÷ height (m)²
For example, an adult who weighs 80 kg and is 1.70 m tall would have a BMI of:
80 ÷ (1.70 × 1.70) = 27.7 kg/m²
If you prefer imperial units, you can multiply your weight in pounds by 703 and then divide by the square of your height in inches.
BMI categories
< 18.5
Underweight
18.5 – 24.9
Healthy Weight
25 – 29.9
Overweight
30 +
Obesity
Three Eligibility Pathways
Which patient group do you fall into?
Our prescribing framework is structured around three distinct clinical pathways, each with its own minimum BMI threshold. This reflects evidence-based guidance from NICE and adapts it for safe, continuous private weight-management care.
Pathway 1 — New Starter
Beginning prescription weight-management treatment for the first time
≥ 30BMI KG/M²
If you are starting treatment with a GLP-1 receptor agonist such as tirzepatide (Mounjaro) or semaglutide (Wegovy) for the very first time, you must meet one of the eligibility criteria below.
- BMI of 30 kg/m² or above — the standard clinical definition of obesity, and the principal entry point for treatment under the licensed indication.
- BMI of 27 kg/m² or above in the presence of at least one weight-related comorbidity (see the checklist below).
- For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds: BMI 27.5 or above, or BMI 24.5 to below 27.5 with at least one weight-related comorbidity.
Pathway 2 — Switching Provider
Already established on treatment with another UK provider
≥ 21BMI KG/M²
If you are already receiving a licensed GLP-1 weight-management medicine through another UK-regulated prescriber and wish to transfer your care to us, we may continue your treatment at a current BMI as low as 21 kg/m².
- Documented prescription history from a CQC-registered clinic or GPhC-registered pharmacy in the UK.
- Evidence of clinical response — typically a sustained weight loss of at least 5% from your starting weight while on treatment.
- Original starting BMI that met the criteria for initiation under Pathway 1.
- No new contraindications — your medical history will be re-reviewed by our prescriber as part of the transfer.
Pathway 3 — Maintenance Management
Continuing low-dose treatment to preserve weight loss
≥ 20BMI KG/M²
For patients who have successfully reached or are approaching their target weight, our maintenance pathway supports the long-term preservation of weight loss using a stable, lower dose.
- Current BMI of 20 kg/m² or above — this floor exists to protect against the risks associated with becoming underweight.
- Stable weight over the previous 8–12 weeks (i.e. plateau reached).
- Maintenance-dose prescribing — typically the lowest effective dose, rather than continued escalation.
- Ongoing clinical review at each prescription cycle, including weight, blood pressure, and any new symptoms.
Have you been diagnosed with any of these medical conditions?
The presence of any of the conditions below alongside a BMI of 27 kg/m² or above (or 24.5 kg/m² for the listed ethnic backgrounds when at least one weight-related condition is present) means you may be eligible to begin treatment without needing to reach the higher BMI 30 threshold.
What to consider: Think about formal diagnoses given to you by a GP, hospital doctor, or specialist — not symptoms you suspect but have not had investigated. Past diagnoses still count, even if you are no longer receiving treatment for them.
Type 2 Diabetes — Whether managed through diet alone, tablets, or insulin. Please tick this if you have ever been diagnosed.
Pre-diabetes or insulin resistance — A blood test result showing your sugar level is higher than normal but not yet in the diabetes range, or a previous diagnosis of metabolic syndrome.
High blood pressure (hypertension) — A diagnosis made by a clinician, or any medication you currently take to lower your blood pressure.
Raised cholesterol or triglycerides — A diagnosis of high cholesterol, or currently taking a statin or other medication to lower your cholesterol.
Cardiovascular disease — Includes angina, coronary artery disease, a previous stent or bypass operation, or a diagnosis of heart failure.
Obstructive sleep apnoea (OSA) — A diagnosis confirmed by a sleep study. Please indicate if you currently use a CPAP machine at night.
Osteoarthritis of the hips or knees — Particularly where a clinician has suggested that losing weight would help to ease your symptoms.
Start Your Consultation →
Your answers are confidential and used only for the purposes of clinical assessment by a UK-registered prescriber.
Ethnicity-Adjusted Thresholds
Why lower BMI thresholds may apply to some ethnic backgrounds may apply to some ethnic backgrounds
BMI was originally designed using data from white European populations, but research has consistently shown that weight-related health problems can begin to develop at a lower BMI in people from certain ethnic backgrounds. To reflect this, NICE guidance (NG246, 2025) recommends a BMI threshold that is around 2.5 points lower for the following groups:
How This Differs From the NHS
NHS criteria are stricter than Happy Pharmacy's
NHS commissioning rules are designed around population-level cost-effectiveness and rationing, whereas a regulated private prescriber follows the licensed indication of the medicine and the relevant NICE technology appraisals (TA875 for semaglutide; TA1026 for tirzepatide). The thresholds for accessing treatment privately are therefore generally lower. Read our NHS weight loss injection eligibility guide for a fuller comparison.
Why These Thresholds?
The evidence underpinning each pathway
These thresholds reflect the licensed indications of the medicines, the relevant NICE technology appraisals, and the long-term cohort and trial evidence on cardiometabolic risk in different populations.
South Asian
Chinese
Other Asian
Middle Eastern
Black African
African-Caribbean
If you are of mixed background, a prescriber will use clinical judgement, taking into account your full medical and family history rather than a single threshold figure.
NHS
Specialist Weight-Management Service
- BMI ≥ 35 kg/m² with at least one weight-related condition (BMI 30–34.9 only under very specific tier-3/tier-4 criteria).
- Referral required from your GP into a tier-3 multidisciplinary service.
- Typical waiting times of 6–18 months depending on local commissioning.
- Maximum treatment duration capped at two years under TA875.
- Requires evidence of prior structured lifestyle intervention.
- Tirzepatide being rolled out in stages — highest BMI groups offered it first.
HAPPY
Happy Pharmacy
- BMI ≥ 30, or ≥ 27 with a co-morbidity. For the listed ethnic backgrounds, these thresholds are usually reduced by 2.5 points.
- Direct online consultation — no GP referral required.
- Typical clinical review within 24–48 hours of submission.
- Duration determined by individual clinical response, not a hard cap.
- Lifestyle support offered alongside treatment, but not a prerequisite.
- Switching and maintenance pathways available for continuity of care.
01BMI 30Obesity thresholdThe point at which all-cause mortality and the risk of type 2 diabetes, cardiovascular disease, and several cancers rise substantially.
02BMI 27Co-morbidity thresholdIn the STEP and SURMOUNT trials, BMI ≥ 27 was the inclusion criterion when a weight-related condition was present.
03BMI 27.5 / 24.5 + conditionEthnicity-adjustedNICE NG246 recognises lower BMI cut-offs for South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean groups. A weight-related condition is still required between BMI 24.5 and 27.5.
04BMI 21Switching floorReflects the clinical reality that established patients have already responded to treatment. Abrupt discontinuation correlates with rapid weight regain.
05BMI 20Maintenance floorSits safely above the underweight threshold of 18.5 kg/m². Below this point, continued GLP-1 therapy is not considered clinically appropriate.
06MHRA / GPhCRegulatory frameworkAll treatments dispensed are MHRA-approved. All prescribing follows GPhC standards. Side effects reportable via the Yellow Card scheme.
Frequently Asked Questions
FAQs
Answers to the questions we are most often asked about BMI and weight-loss treatment eligibility.
BMI (Body Mass Index) is a number worked out from your height and your weight, using the formula BMI = weight (kg) ÷ height (m)². It gives a quick estimate of whether your weight sits within a healthy range for someone of your size. The standard categories are: under 18.5 (underweight), 18.5–24.9 (healthy weight), 25–29.9 (overweight), and 30 or above (obesity).
BMI does not measure body fat directly, but at a population level it gives a reliable indication of how much body fat a person is likely to be carrying. As BMI rises above the healthy range, so does the risk of long-term health problems such as type 2 diabetes, high blood pressure, heart disease, stroke, certain cancers, and joint problems. The BMI thresholds used in prescribing also match the populations studied in the major clinical trials of these medicines.
For new patients starting treatment for the first time, you usually need a BMI of 30 or above. You may also qualify with a BMI of 27 or above if you have at least one weight-related health condition. If you are from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, the thresholds are usually 27.5 or above, or 24.5 to below 27.5 with at least one weight-related health condition. If you are switching from another provider or already in maintenance treatment, the thresholds are lower again.
No — a BMI of 27 alone is not enough on its own. To qualify at this BMI you must also have a documented weight-related health condition, such as type 2 diabetes, high blood pressure, raised cholesterol, cardiovascular disease, obstructive sleep apnoea, osteoarthritis, or another condition recognised as linked to excess weight. Eligibility is always confirmed during a clinician-led consultation.
For first-time patients, treatment is not usually recommended below a BMI of 27. However, if you are already receiving treatment from another UK-regulated prescriber and wish to transfer your care, we may accept you with a current BMI as low as 21. If you have already lost weight on treatment and are stable at or near your target weight, our maintenance pathway supports continued low-dose prescribing down to a BMI of 20.
If you enter your height and weight correctly, the calculator will work out your BMI accurately using the standard formula. However, BMI itself has limitations: it does not tell the difference between muscle and fat, and the standard thresholds may need to be adjusted for some ethnic backgrounds. For this reason, your BMI should always be looked at alongside the rest of your medical picture.
No — the calculator gives you an indication of whether your BMI meets the usual thresholds, but it cannot confirm eligibility on its own. Final eligibility is decided by a GPhC-registered prescriber after a full online consultation, which takes into account your medical history, any weight-related health conditions, current medications, and your ethnic background.
No — BMI is the starting point, but a clinician will always look at the whole picture. This includes your full medical history, any weight-related health conditions, any other medicines you are currently taking, and your ethnic background. If you are switching from another provider, your prescriber will also review evidence of your response to previous treatment.
NHS criteria are stricter and apply through a tier-3 or tier-4 specialist weight-management service. To access NHS treatment you usually need a BMI of 35 or above with at least one weight-related condition, a GP referral, and evidence of prior structured lifestyle intervention — with treatment capped at two years. Private prescribing follows the licensed indication of the medicine and is accessed directly through an online consultation with no GP referral and no two-year cap.
The next step is to complete our secure online consultation, where you will be asked about your weight history, any medical conditions, your current medications, and other relevant background. A GPhC-registered prescriber will then review your answers and decide whether prescription weight-loss treatment is appropriate for you. If it is, your prescriber will discuss the most suitable medicine and arrange ongoing reviews to monitor your progress.
References
This consultation is medically reviewed by GPhC-registered pharmacists and independent prescribers. Last reviewed: May 2026. Next scheduled review: November 2026. Medication is prescribed following a consultation with a qualified prescriber. Read the official patient information, including safety advice, for Mounjaro and Wegovy.
- NICE. Overweight and obesity management. NICE guideline NG246. 2025. nice.org.uk/guidance/ng246
- NICE. Semaglutide for managing overweight and obesity. Technology appraisal TA875. 2023. nice.org.uk/guidance/ta875
- NICE. Tirzepatide for managing overweight and obesity. Technology appraisal TA1026. 2024. nice.org.uk/guidance/ta1026
- NHS. Body mass index (BMI) and healthy weight. nhs.uk
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). NEJM. 2021;384:989–1002.
- Rubino D et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance (STEP 4). JAMA. 2021;325(14):1414–1425.
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM. 2022;387:205–216.
- Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). NEJM. 2023;389:2221–2232.