The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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What Are the BMI Requirements for Mounjaro in the UK?
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK, but you need to meet specific BMI requirements to be eligible. The primary requirement is a BMI of 30 or above. However, if you have weight-related health conditions like type 2 diabetes, high blood pressure, or heart disease, you may be eligible with a BMI of 27 or above. These thresholds follow NHS guidance and are designed to prioritise treatment for those at greatest health risk. Your GP or a licensed prescriber will assess your individual circumstances to determine suitability.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
UK BMI Thresholds for Mounjaro Eligibility
The standard BMI requirement for Mounjaro in the UK is 30 kg/m² or above. This aligns with the NHS definition of obesity. However, you may be eligible at a lower BMI of 27 to 29.9 if you have a weight-related health condition, such as:
- Type 2 diabetes or prediabetes
- High blood pressure (hypertension)
- Abnormal blood lipids (dyslipidaemia)
- Obstructive sleep apnoea
- History of heart attack, stroke, or cardiovascular disease
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recognises lower health thresholds, and eligibility may begin at a BMI of 27.5 or above, even without additional comorbidities. Use our free BMI calculator above to check your current BMI and see where you fall within these ranges. A prescriber will always assess your individual health profile before deciding if Mounjaro is appropriate for you.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
BMI Limitations and What Else Matters
BMI is a screening tool, not a complete picture of your health. It does not distinguish between muscle mass and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. Waist circumference is also important: the NHS recommends measuring waist size as a complementary indicator. For men, over 94 cm (37 inches) indicates increased health risk; over 102 cm (40 inches) indicates high risk. For women, over 80 cm (31.5 inches) is increased risk; over 88 cm (34.5 inches) is high risk. Your prescriber may ask about your waist measurement, family history, lifestyle, and existing health conditions alongside your BMI to make a comprehensive assessment. Try our GLP-1 weight loss calculator to explore potential outcomes if you are considering Mounjaro.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can I get Mounjaro with a BMI of 28?
Only if you have a weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Without a comorbidity, standard eligibility begins at BMI 30. Those of South Asian or Black African heritage may be eligible at BMI 27.5. A prescriber will assess your individual circumstances.
What is the BMI formula used in the UK?
The standard BMI formula is weight (kg) divided by height (metres) squared. For example, if you weigh 85 kg and are 1.75 m tall, your BMI is 85 ÷ (1.75 × 1.75) = 27.8. Our BMI calculator works this out instantly for you.
How do I know if my BMI falls within the healthy range?
According to NHS guidelines, a healthy BMI is 18.5 to 24.9 for most adults. For people of South Asian or Black African heritage, the healthy range is 18.5 to 22.9. You can check your personal BMI using our free calculator on this page.
Does waist measurement affect Mounjaro eligibility?
While BMI is the primary eligibility criterion, waist circumference is often considered too. High waist circumference (over 94 cm for men, 80 cm for women) indicates increased health risk and may strengthen your case for treatment, especially at lower BMIs.
Can my BMI change after starting Mounjaro?
Yes. As you lose weight on Mounjaro, your BMI will decrease. Many people achieve a healthy BMI range through the medication combined with lifestyle changes. You can track your progress and updated BMI using our free progress tracker.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.