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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Average Mounjaro Weight Loss — Clinical Evidence
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Clinical trials show that adults taking Mounjaro lost an average of 15% to 21% of their body weight over 72 weeks — though individual results vary significantly. Weight loss depends on several factors including starting weight, dose, diet, activity level, and how long you've been taking the medication. This guide explains what the evidence shows about average weight loss, how results compare to other options, and what affects your personal outcomes.
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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.
What Do Clinical Trials Show About Average Weight Loss?
The SURMOUNT-1 clinical trial is the main evidence for Mounjaro's weight loss effects. At 72 weeks, participants achieved the following average weight loss results:
- 5 mg dose: approximately 15% of body weight
- 10 mg dose: approximately 19.5% of body weight
- 15 mg dose: approximately 20.9% of body weight
To put this in practical UK terms: an adult starting at 100 kg (15 stone 10 lbs) taking the maximum 15 mg dose might lose around 21 kg (3 stone 4 lbs) over the trial period. However, these are average results alongside a reduced-calorie diet and increased physical activity — actual weight loss varies between individuals. Some people lose more, some lose less. Your GP or prescriber can discuss realistic expectations for your situation using our free GLP-1 weight loss calculator.
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.
What Affects Your Personal Weight Loss Results?
Several factors influence how much weight you personally lose on Mounjaro, regardless of the average figures. Your starting weight matters — people with higher starting weight often lose larger amounts. Dose strength is important too: the 15 mg maximum dose typically produces better results than lower doses like 5 mg or 10 mg. Your lifestyle choices are critical — weight loss injections work best alongside a reduced-calorie diet and regular physical activity. How long you take it affects outcomes: most clinical trial results come from 72 weeks of treatment. Individual metabolism, medical conditions, and medications you're already taking also play a role. Your prescriber will assess your individual circumstances and help set realistic targets during your clinical assessment.
- 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 do most people lose on Mounjaro?
On average, clinical trials showed weight loss of 15–21% of body weight over 72 weeks at different doses. This means someone weighing 100 kg might lose approximately 15–21 kg on average. However, individual results vary significantly based on starting weight, dose, diet, activity, and other personal factors.
Is Mounjaro weight loss assured?
No. While clinical trials showed average weight loss, not everyone responds the same way. Mounjaro is a tool that works alongside lifestyle changes — it's not a assured solution. Some people lose more than average, some lose less. Your GP will discuss realistic expectations during your assessment.
How does Mounjaro compare to Wegovy for weight loss?
Clinical trials show Mounjaro (15 mg) achieved approximately 20.9% average weight loss, while Wegovy (semaglutide) achieved approximately 14.9% average weight loss. However, these are separate trials with different populations — direct comparison is complex. Both are prescription-only and require clinical assessment.
How long before you see average Mounjaro weight loss results?
Weight loss typically begins within the first 2–4 weeks as your dose increases, but significant results develop over weeks 8–16 as you reach maintenance doses. The clinical trial results span 72 weeks, so expect a gradual process alongside consistent diet and activity changes.
Should I use a weight loss calculator to estimate my results?
Yes — our free GLP-1 weight loss calculator can help you estimate potential outcomes at different Mounjaro doses based on clinical trial data. However, this is an estimate only. Your actual results will depend on your individual response, adherence, and lifestyle factors. Always discuss realistic expectations with your prescriber.
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.