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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Mounjaro vs Wegovy: Calculator Comparison for UK Adults
If you're considering GLP-1 weight loss treatment in the UK, comparing Mounjaro (tirzepatide) and Wegovy (semaglutide) is an important first step. Both are prescription-only injections approved for adults with obesity or overweight plus health conditions, but they work differently and produce different average results. Our GLP-1 weight loss calculator above can help you explore potential outcomes, while this guide explains the key differences between these two medications to help inform your conversation with a prescriber.
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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.
How Mounjaro and Wegovy Differ: Mechanism, Doses, and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may help explain why clinical trials showed higher average weight loss. In the SURMOUNT-1 trial, participants on the maximum 15 mg dose lost approximately 20.9% of their body weight over 72 weeks. The dose range runs from 2.5 mg up to 15 mg, increasing weekly or every four weeks depending on individual tolerance.
Wegovy (semaglutide) works as a single GLP-1 receptor agonist — activating one pathway. In the STEP-1 trial, the 2.4 mg maintenance dose achieved approximately 14.9% average weight loss over 68 weeks. Wegovy starts at 0.25 mg and titrates up to the maximum 2.4 mg dose. Both medications are once-weekly injections delivered via pre-filled pen (Mounjaro as a KwikPen, Wegovy as an auto-injection pen).
- Mounjaro: Dual mechanism, higher trial weight loss average, maximum 15 mg
- Wegovy: Single mechanism, lower trial average, maximum 2.4 mg
- Both: Once-weekly injection, prescription-only, require clinical assessment
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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.
Which Is Right for You? Suitability and Prescriber Guidance
There is no "better" choice between Mounjaro and Wegovy — suitability depends entirely on individual medical history, previous medications, and how your prescriber assesses your particular situation. Eligibility for both medications is identical: you must have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Both require a prescription and clinical assessment — neither can be accessed without one.
Use our free BMI calculator to check whether you fall within typical eligibility ranges. Your prescriber will review your full health picture, including any other medications you take (particularly oral contraceptives, which both medications may affect), and decide which option is appropriate for you. Some patients may be switched between the two if one is not tolerated well or results plateau.
Both medications work best alongside sustainable dietary changes and increased physical activity — they are not replacements for lifestyle changes. Track your progress with our free progress tracker throughout your weight loss journey. Remember that individual results vary significantly, even among people at the same dose. A prescriber will discuss realistic expectations, potential side effects (nausea, diarrhoea, and constipation are common to both), and how long treatment typically lasts. If you're interested in exploring potential outcomes, try our GLP-1 weight loss calculator — it can help you understand weight loss projections at different doses, though actual outcomes will be unique to your circumstances.
- 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 use a calculator to decide between Mounjaro and Wegovy?
Calculators like ours help you understand potential weight loss ranges at different doses based on trial data. However, only a prescriber can assess which medication is suitable for your medical history, medications, and individual circumstances. Use our tools to inform your discussion with your GP or prescriber, not to replace their clinical judgment.
Why does Mounjaro show higher weight loss in trials than Wegovy?
The SURMOUNT trial for Mounjaro showed approximately 20.9% average weight loss versus 14.9% for Wegovy in the STEP trial, largely because Mounjaro is a dual GIP and GLP-1 agonist — it activates two hormone pathways rather than one. However, trial conditions and patient populations differ, and individual results vary widely regardless of which medication you take.
Are Mounjaro and Wegovy available on the NHS in the UK?
Yes, both are approved by NICE for NHS use, but access is typically through specialist tier 3 weight management services following GP referral. Waiting lists vary significantly by region. Both are also available privately through UK-registered online prescribing services following a clinical assessment.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is approved for type 2 diabetes (doses up to 2 mg) and using it for weight loss is off-label. Wegovy is specifically licensed for weight management in the UK at doses up to 2.4 mg. Always ensure you're prescribed the correct product for your treatment goal.
How long does treatment with Mounjaro or Wegovy typically last?
There is no set duration — treatment continues as long as it's effective and well-tolerated. Some people use these medications for months, others for years. Your prescriber will review your progress regularly and discuss whether to continue, adjust dose, or stop treatment based on your individual response and health goals.
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.