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 0.5mg Equivalent to Mounjaro?
Wegovy 0.5mg is roughly equivalent to Mounjaro 5mg in terms of clinical potency, though direct dose-for-dose comparison is complex because these medications work through different mechanisms. Wegovy (semaglutide) is a GLP-1 receptor agonist, whilst Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist. Both are prescription-only weight loss injections licensed in the UK. The choice between them depends on individual health circumstances and prescriber assessment, not just dose equivalence. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication.
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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.
Mechanism Differences and Dose Equivalence
Wegovy (semaglutide) activates GLP-1 receptors only, signalling to the brain that you are full, slowing gastric emptying, and reducing hunger hormones. Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors — a dual mechanism that may explain its slightly stronger average weight loss in clinical trials.
Approximate dose equivalence based on clinical practice:
- Wegovy 0.5mg ≈ Mounjaro 5mg (early escalation doses)
- Wegovy 1.7mg ≈ Mounjaro 10mg (mid-range doses)
- Wegovy 2.4mg ≈ Mounjaro 15mg (maximum doses)
Important: These are clinical approximations only. There is no official conversion chart. Any switch between medications must be managed by your prescriber, who will assess your individual response and adjust doses accordingly.
Clinically BackedWeight Loss
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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.
Clinical Trial Outcomes and Individual Variation
In the STEP-1 trial, Wegovy 2.4mg achieved average weight loss of approximately 14.9% of body weight over 68 weeks. In the SURMOUNT-1 trial, Mounjaro 15mg achieved approximately 20.9% average weight loss over 72 weeks. However, individual results vary significantly — some people lose more, some less.
Both medications work best alongside a reduced-calorie diet and increased physical activity. Your GP or licensed prescriber will assess which medication suits your individual circumstances, medical history, and preferences. Calculate your potential weight loss range using our GLP-1 weight loss calculator above, then discuss results with your prescriber.
- 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.
Is Mounjaro stronger than Wegovy?
Clinical trials suggest Mounjaro may produce slightly greater average weight loss (around 20.9% vs 14.9% at maximum doses), likely due to its dual GIP+GLP-1 mechanism versus Wegovy's single GLP-1 mechanism. However, individual responses vary considerably. Suitability depends on your health profile, not potency alone.
Can I switch from Wegovy 0.5mg to Mounjaro?
Yes, but only under prescriber guidance. There is no official conversion chart. Your prescriber will assess your response to Wegovy and may recommend starting Mounjaro at a lower dose (typically 2.5mg) before escalating. Never switch without medical supervision.
Which injection is available on the NHS in the UK?
Both Mounjaro and Wegovy have been approved by NICE for NHS specialist weight management services, but access varies significantly by region and local commissioning. Waiting lists can be lengthy. Private prescribing is available through GPhC-registered online pharmacies following clinical assessment.
What are the main side effects of both injections?
Both commonly cause nausea, diarrhoea, vomiting, and stomach discomfort, especially during dose escalation. These typically ease over time. Serious side effects are rare but include pancreatitis and gallbladder problems. Report persistent severe stomach pain to your GP immediately.
How do I know which medication is right for me?
Your GP or licensed prescriber will assess your BMI, medical history, weight-related conditions, and previous weight loss attempts. They will discuss both medications, their mechanisms, side effect profiles, and cost. Individual suitability cannot be determined from dose equivalence alone — clinical assessment is essential.
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.