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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Wegovy to Mounjaro Conversion — Understanding the Switch
If you're considering switching from Wegovy (semaglutide) to Mounjaro (tirzepatide), you may wonder how doses compare. While approximate dose equivalences exist, there is no official NHS conversion chart. Both are prescription-only weight management injections licensed in the UK, but they work differently — Wegovy is a GLP-1 receptor agonist, whilst Mounjaro is a dual GIP and GLP-1 agonist. Any switch between these medications must be managed by your prescriber following a clinical assessment. Understanding how they compare helps you have an informed discussion with your GP or prescriber about which option might suit you.
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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.
Approximate Dose Equivalence and Clinical Trial Data
There is no official NHS or manufacturer-endorsed conversion between Wegovy and Mounjaro doses. However, clinical practice guidance suggests approximate equivalences based on clinical trial outcomes:
- Wegovy 0.5 mg ≈ Mounjaro 5 mg — both lower starting maintenance doses
- Wegovy 1.7 mg ≈ Mounjaro 10 mg — mid-range escalation doses
- Wegovy 2.4 mg ≈ Mounjaro 15 mg — maximum doses
STEP trial data showed Wegovy 2.4 mg achieved approximately 15% average body weight loss over 68 weeks. SURMOUNT trial data showed Mounjaro 15 mg achieved approximately 21% average body weight loss at 72 weeks. However, individual results vary significantly, and these are averages in controlled trials alongside calorie reduction and increased activity. The difference in mechanisms — Mounjaro's dual GIP+GLP-1 action versus Wegovy's single GLP-1 action — may contribute to different outcomes between individuals.
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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? Prescriber Assessment and Suitability
Choosing between Wegovy and Mounjaro is not about which is "better" — it's about which suits your individual health, medical history, and circumstances. Your GP or prescriber will assess factors including your eligibility (BMI, weight-related health conditions, ethnic background), current medications, any previous experience with GLP-1 medications, and whether you've used either medication before. If you've been taking Wegovy without side effects, switching may not be necessary. If you're interested in switching, discuss your reasons with your prescriber — they can advise whether a change is clinically appropriate. Both require ongoing monitoring, and both are used alongside reduced-calorie diet and increased physical activity for best results. Try our GLP-1 weight loss calculator to explore potential outcomes, and use the BMI calculator to understand your starting point.
- 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 more effective than Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (21% vs 15%), but individual results vary. Effectiveness depends on your personal response, medical history, lifestyle, and adherence. Your prescriber will discuss which suits you best.
Can I switch directly from Wegovy to Mounjaro at the equivalent dose?
No. Switching requires prescriber guidance. You cannot simply move to an "equivalent" dose — your prescriber will typically restart at a lower Mounjaro dose (2.5 mg) and titrate upward, even if you were on a high Wegovy dose.
What's the difference between Wegovy and Mounjaro?
Wegovy is a GLP-1 agonist only; Mounjaro is a dual GIP and GLP-1 agonist. This dual mechanism may affect appetite, glucose control, and weight loss differently. Both require prescriptions and clinical assessment.
Why do approximate dose conversions exist if they're not official?
Approximate equivalences help prescribers make informed switching decisions based on clinical experience and trial data. However, every patient responds differently, so switches are individualised, not formulaic.
Is NHS tirzepatide (Mounjaro) prescribed differently from private prescriptions?
Yes. NHS access is through tier 3 specialist weight management services with regional variation and waiting lists. Private prescriptions are through GPhC-registered online services. Eligibility, monitoring, and support may differ between pathways.
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.