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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Mounjaro Average Weight Loss — Clinical Data
Mounjaro (tirzepatide) helped participants lose an average of 15% to 21% of their body weight in clinical trials, though individual results vary significantly. For a person weighing 100kg (15st 10lbs), this could mean losing 15–21kg (2st 5lbs to 3st 5lbs) over 72 weeks. However, actual weight loss depends on the dose, adherence, diet, exercise, and individual metabolism. This guide explains the real data behind Mounjaro's weight loss and what to expect.
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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 — What the SURMOUNT Studies Show
The SURMOUNT-1 clinical trial is the primary evidence for Mounjaro's weight loss in the UK. Over 72 weeks, participants receiving Mounjaro alongside a reduced-calorie diet and increased physical activity achieved:
- 5mg dose: approximately 15% average body weight loss
- 10mg dose: approximately 19.5% average body weight loss
- 15mg dose: approximately 20.9% average body weight loss (maximum dose)
For context, a person weighing 80kg (12st 8lbs) losing 15% would weigh approximately 68kg (10st 10lbs). At 20.9%, they would weigh around 63kg (9st 13lbs). Importantly, these are averages — some participants lost more, others less. The placebo group lost approximately 3% on average, showing that Mounjaro's effect is significantly greater than diet and exercise alone, but medication is not a substitute for lifestyle changes.
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 Individual Weight Loss
Your personal weight loss with Mounjaro depends on several factors beyond the medication itself:
- Starting weight and metabolism: Metabolic rate varies between individuals and with age
- Adherence to diet: Mounjaro reduces appetite, but calorie deficit is still essential
- Physical activity: Regular exercise amplifies weight loss and preserves muscle mass
- Dose and duration: Higher doses and longer treatment typically produce greater results
- Genetics and medical conditions: Conditions like thyroid disorders or PCOS may affect outcomes
Use our free GLP-1 weight loss calculator to estimate your potential weight loss at different doses. Calculate your current healthy weight range with our BMI calculator, and track your progress using our free progress tracker.
- 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 at maintenance doses. However, individual results vary significantly. Your actual loss depends on starting weight, dose, diet adherence, exercise, and metabolism. Only a healthcare professional can estimate your personal outcome.
Is 15–clinically studied weight loss realistic for me?
These percentages are trial averages — realistic for many, but not assured for all. Factors like your starting weight, how well you stick to diet changes, physical activity level, and how your body responds to the medication all matter. Your GP or prescriber can discuss realistic expectations based on your situation.
How long does it take to see weight loss on Mounjaro?
Most people notice appetite reduction within days or weeks, but significant weight loss typically takes 4–12 weeks. The SURMOUNT trial measured results over 72 weeks, so sustained treatment at a stable dose produces the best outcomes. Patience and consistency are key.
What's the difference between 5mg, 10mg, and 15mg weight loss?
Higher doses generally produce greater average weight loss: 5mg ≈15%, 10mg ≈19.5%, 15mg ≈20.9%. However, not everyone tolerates higher doses, and some people achieve their goals at lower doses. Your prescriber will determine the right dose for you.
What happens to weight loss after stopping Mounjaro?
Clinical trials show that weight lost on Mounjaro can regain if treatment stops without sustained lifestyle changes. Weight maintenance requires ongoing dietary habits and physical activity. Some people continue treatment long-term; others transition to maintained diet and exercise. Discuss your long-term plan with your GP.
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.