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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Expected Weight Loss With Mounjaro
If you're considering Mounjaro (tirzepatide) for weight management in the UK, you'll want to know what realistic weight loss to expect. Clinical trials showed that adults using Mounjaro lost an average of 15% to 21% of their body weight over 72 weeks, though individual results vary significantly. This guide explains the evidence behind these figures, how dose affects outcomes, and what factors influence your personal results. Remember, Mounjaro is a prescription-only medicine requiring a clinical assessment, and weight loss works best alongside dietary changes and increased physical activity.
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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 Results and Dose-Dependent Outcomes
The SURMOUNT-1 clinical trial — the main UK-referenced trial for Mounjaro — tracked weight loss across different doses over 72 weeks. At the maximum dose of 15 mg weekly, participants lost an average of 20.9% of their body weight. At 10 mg weekly, average loss was approximately 19.5%, and at the lower 5 mg dose, around 15%. These figures are substantial: for someone weighing 100 kg (15st 10lbs), a 20% loss would mean approximately 20 kg (3st 2lbs) weight reduction.
- 5 mg dose: ~clinically studied weight loss on average
- 10 mg dose: ~clinically studied weight loss on average
- 15 mg dose: ~clinically studied weight loss on average
However, these are trial averages — your individual result depends on adherence to the medication, dietary changes, exercise, genetics, and baseline metabolism. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses for your starting weight.
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.
Factors Affecting Your Personal Weight Loss
Not everyone achieves the average result, and that's normal. Weight loss with Mounjaro depends on several factors: how strictly you follow a reduced-calorie diet, your baseline weight (heavier individuals often lose more kg), your age and metabolism, whether you're physically active, genetic predisposition, and how long you stay on the medication. Many people also experience reduced appetite initially, which fades slightly over time — this is expected.
Dose titration matters too. Mounjaro starts at 2.5 mg and increases gradually over weeks. People who escalate to higher doses typically achieve greater weight loss. Your GP or prescriber will assess whether you should reach the maximum 15 mg dose or maintain a lower dose that works for you. Track your progress using our free progress tracker to monitor your personal results over time.
- 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.
How much weight will I lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, depending on dose. However, individual results vary significantly based on diet, exercise, genetics, and adherence. A prescriber can discuss realistic expectations for your situation during your clinical assessment.
Is clinically studied weight loss realistic for everyone?
No. The 20.9% figure from SURMOUNT-1 at 15 mg is a trial average. Some people lose more, others less. Weight loss depends on calorie deficit, lifestyle changes, metabolism, and how your body responds to the medication. Results are not assured.
How long does it take to see weight loss on Mounjaro?
Most people notice appetite reduction within the first few weeks, but measurable weight loss typically becomes apparent over 4–8 weeks. Significant weight loss usually develops over months. Mounjaro works best as part of a long-term approach alongside diet and exercise.
Is Mounjaro better than Wegovy for weight loss?
Mounjaro (dual GIP/GLP-1 agonist) showed slightly higher average weight loss than Wegovy (GLP-1 agonist only) in different trials — around 21% versus 15% on average. However, individual response varies. Your prescriber will recommend the most suitable option for you based on your health profile.
Can I lose weight faster with a higher dose?
Higher doses (10 mg, 15 mg) showed greater average weight loss than lower doses in trials. However, higher doses also increase side effect risk. Your prescriber will titrate you gradually to find the balance between effectiveness and tolerability for your individual needs.
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.