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
Free tracker included with every download this week
Is Wegovy or Mounjaro Better for Weight Loss?
Neither medication is universally "better" — the right choice depends on your individual health, NHS access, and prescriber recommendation. Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weekly weight loss injections licensed in the UK. Wegovy is a GLP-1 receptor agonist, whilst Mounjaro works through a dual GIP and GLP-1 mechanism. Clinical trials show both can help with weight loss alongside diet and exercise, but individual results vary significantly. Your GP or a licensed prescriber will assess which medication, if either, is appropriate for you based on your personal health profile and eligibility criteria.
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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.
Clinical Trial Data and NHS Eligibility Context
Mounjaro (tirzepatide) showed average weight loss of 20.9% of body weight at the maximum 15 mg dose over 72 weeks in the SURMOUNT-1 trial. Wegovy (semaglutide) showed average weight loss of 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks in the STEP-1 trial. However, these are clinical trial averages — individual outcomes vary considerably based on adherence, diet, exercise, and personal factors.
Both are approved by NICE for NHS use through tier 3 specialist weight management services. NHS eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. Access through the NHS can involve waiting lists; private prescription routes are faster but cost approximately £129–£320 monthly depending on dose.
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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.
How to Choose: NHS Access and Practical Considerations
If you're accessing treatment through the NHS, your prescriber will determine which medication is suitable based on your medical history, not personal preference. Mounjaro dose titration begins at 2.5 mg weekly, escalating to a maximum of 15 mg, whilst Wegovy starts at 0.25 mg, reaching a maximum 2.4 mg weekly dose. Mounjaro's dual mechanism may suit some patients better, but Wegovy's longer clinical track record and established safety profile appeal to others.
Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses. Your GP or a licensed prescriber can assess your eligibility, discuss side effects, and recommend the most appropriate option. Neither medication assures weight loss — success depends on commitment to lifestyle changes alongside pharmacological support.
- 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.
Which weight loss injection is more effective — Wegovy or Mounjaro?
Clinical trials show Mounjaro (tirzepatide) achieved slightly higher average weight loss (~21% body weight) compared to Wegovy (~15%), but individual results vary significantly. Effectiveness depends on adherence, diet, exercise, and personal metabolism — not the medication alone. Both are effective when used with lifestyle changes.
Can I get Mounjaro or Wegovy through the NHS in the UK?
Yes, both are NICE-approved for NHS use through tier 3 specialist weight management services. Access requires referral from your GP and assessment by a specialist team. Eligibility criteria include BMI ≥30 or ≥27 with weight-related health conditions. Availability and waiting times vary significantly by region and ICB.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro has a dual mechanism, whilst Wegovy operates through a single pathway. Maximum doses differ: Mounjaro 15 mg weekly versus Wegovy 2.4 mg weekly. Both are once-weekly injections.
How much do Mounjaro and Wegovy cost privately in the UK?
Private costs typically range from £129–£320 per month depending on dose and provider. The actual cost varies by starting dose and how quickly you escalate. NHS access is free but involves potentially lengthy waiting lists. Costs also vary between different online prescribing services.
Which medication has fewer side effects — Mounjaro or Wegovy?
Both have similar side effect profiles, with nausea, diarrhoea, and constipation being most common. Individual tolerance varies — some people tolerate one better than the other. Your prescriber will monitor side effects and adjust your dose or medication if needed. Side effects typically reduce as your body adjusts.
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.