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
What's the Average Weight Loss on Mounjaro?
Clinical trials show that adults taking Mounjaro (tirzepatide) lost an average of 15 to 21% of their body weight over 72 weeks, depending on the dose used. However, individual results vary significantly — some people lose more, some less. Weight loss on Mounjaro is not assured and depends on many factors including your starting weight, diet, physical activity, and how your body responds to the medication. This guide explains the clinical data, what "average" means in real terms, and the factors that influence your personal weight loss outcome.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 — Mounjaro Weight Loss Data
The SURMOUNT-1 clinical trial, which tested Mounjaro in adults with obesity, found these average weight loss results over 72 weeks:
- 5 mg dose: approximately clinically studied weight loss
- 10 mg dose: approximately clinically studied weight loss
- 15 mg dose: approximately clinically studied weight loss
To illustrate in UK measurements: an adult weighing 100 kg (15 stone 10 lbs) taking the maximum 15 mg dose might expect to lose around 21 kg (3 stone 4 lbs) on average. A person at 80 kg (12 stone 8 lbs) might lose approximately 17 kg (2 stone 9 lbs). These results were achieved alongside a reduced-calorie diet and increased physical activity — medication alone is not responsible for weight loss. Individual results vary considerably; some participants lost significantly more, whilst others lost less.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 That Affect Your Individual Weight Loss
Your personal weight loss on Mounjaro depends on multiple factors beyond the medication itself. Your starting weight, age, metabolic rate, genetics, and how consistently you follow dietary and exercise changes all play a role. South Asian, Black African, Caribbean, and Chinese adults may experience different metabolic responses. Women and men sometimes show different average weight loss patterns. Medical conditions like type 2 diabetes, polycystic ovary syndrome (PCOS), and thyroid disorders can affect results. Additionally, adherence to your prescribed dose, how your body tolerates the medication, and whether you experience side effects like nausea or reduced appetite all influence outcomes. Your GP or prescriber can discuss realistic expectations based on your individual circumstances using our free BMI calculator to assess 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.
What does "average weight loss" really mean for me?
"Average" refers to the mean result across all trial participants. Some lost more, some less. Your personal outcome will be unique based on your body, lifestyle, dose adherence, and how you respond to the medication. Even if the average is 20%, you might lose 10% or 30% — the range is wide.
Can I expect to lose weight like the clinical trials show?
Clinical trial results are achieved with professional support, monitored reduced-calorie diets, and regular activity — a structured environment. Real-world results often differ. Weight loss still requires consistent dietary changes and exercise alongside medication for best outcomes.
How much weight might I lose in the first month?
Weight loss is usually gradual. In the first month, you might lose 1–2 kg (2–4 lbs) as your body adjusts. Most significant weight loss occurs between weeks 8–16 as your dose increases. Patience is important; this is a marathon, not a sprint.
Does everyone on Mounjaro lose weight?
Not everyone experiences significant weight loss. Some people are non-responders and may lose little or no weight despite being on the medication. Your prescriber will monitor progress and discuss options if weight loss plateaus after several months.
How can I track whether my weight loss is "average"?
Use our free progress tracker to log your weight weekly and monitor your trend over 12+ weeks. Our GLP-1 weight loss calculator can also estimate potential weight loss at different doses based on your starting weight, helping you set realistic expectations.
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.