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 Results Can You Expect From Mounjaro Injections?
Mounjaro (tirzepatide) is a prescription-only weekly injection that has shown significant weight loss results in clinical trials. However, individual results vary considerably, and weight loss depends on factors including your starting weight, dose, diet, and physical activity level. Understanding realistic expectations—based on evidence rather than marketing claims—helps you make an informed decision about whether this medication might be right for you. This guide covers trial data, timelines, and what the NHS says about prescription weight loss treatment in the UK.
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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 Average Weight Loss
The SURMOUNT-1 clinical trial, which tested Mounjaro for weight management, showed average weight loss results over 72 weeks:
- 5 mg dose: approximately 15% of body weight lost on average
- 10 mg dose: approximately 19.5% of body weight lost on average
- 15 mg dose: approximately 20.9% of body weight lost on average (maximum dose)
These results were achieved when participants also followed a reduced-calorie diet and increased their physical activity. For reference, a person weighing 100 kg losing 15% of body weight would lose approximately 15 kg (about 2 stone 5 lbs). However, it's crucial to understand that these are trial averages—some participants lost more, others lost less. Weight loss with any weekly weight loss injection depends heavily on your individual metabolism, adherence to lifestyle changes, and how your body responds to the medication.
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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.
Timeline: When Do Mounjaro Results Appear?
Weight loss with Mounjaro is not immediate. Most people experience modest weight loss in the first 4 weeks while taking the starting dose (2.5 mg), with more noticeable results after 8–12 weeks as doses increase. The dose titration schedule means you increase your injection dose every 4 weeks: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg. Maximum weight loss typically occurs around 12–16 weeks into treatment. Use our free GLP-1 weight loss calculator above to project potential results at different doses. Remember that sustainable weight loss is gradual—rapid loss is not the goal and can indicate muscle loss rather than fat loss. Your GP or prescriber can discuss realistic timelines for your individual situation.
- 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 percentage of body weight do most people lose with Mounjaro?
In the SURMOUNT-1 trial, the average was 15–21% of body weight depending on the dose used. At the maximum 15 mg dose, participants lost around 20.9% on average. However, results vary significantly between individuals. Some lost more, others lost less. These results were achieved alongside dietary changes and increased physical activity, not from the injection alone.
How quickly will I see results from Mounjaro?
Most people notice modest changes within 2–4 weeks, but more significant results typically appear after 8–12 weeks as your dose increases through the titration schedule. Maximum weight loss is usually seen around 12–16 weeks. Weight loss is gradual and sustainable—this is preferable to rapid loss, which can include muscle loss. Your prescriber will monitor your progress.
Is Mounjaro better than Wegovy for weight loss results?
Mounjaro (tirzepatide, dual GIP/GLP-1) and Wegovy (semaglutide, GLP-1 only) showed similar average weight loss in trials—approximately 15–21% and 14.9% respectively. Mounjaro may have a slight advantage in some people, but individual results vary. Your prescriber will assess which is more suitable for you based on your health profile.
Can I use the MyWeightCheck BMI calculator to track my progress with Mounjaro?
Yes. Our free BMI calculator helps you track how your BMI changes as you lose weight on Mounjaro. You can also use our free progress tracker to log your weight loss journey week by week. Regular tracking can help you see trends and stay motivated, even when progress feels slow.
Will I keep the weight off after stopping Mounjaro?
Weight regain is common if lifestyle changes aren't maintained after stopping any weight loss medication. Clinical data shows that people who maintain dietary changes and physical activity are more likely to sustain results. Your GP or prescriber can discuss long-term management strategies and whether continued treatment might be appropriate for you.
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.