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
Does Mounjaro Always Work for Weight Loss?
Mounjaro (tirzepatide) does not work equally for everyone. Clinical trials showed an average weight loss of 15–21% of body weight, but individual results vary significantly. Some people see substantial weight loss, whilst others experience more modest results. Success depends on your body's response to the medication, how well you follow dietary and lifestyle changes, and your starting point. Your GP or prescriber can help assess whether Mounjaro is likely to be effective for you personally.
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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 the Clinical Evidence Actually Shows
Mounjaro's effectiveness is supported by the SURMOUNT clinical trials, which followed adults for 72 weeks. On average, participants taking the maximum 15 mg dose lost approximately 20.9% of their body weight—equivalent to roughly 18–20 kg for someone starting at 85 kg. However, these are average figures, and individual outcomes ranged widely.
The trials also showed that some participants lost very little weight despite taking the medication consistently. Response variation is normal with any weight loss medication. Factors affecting whether Mounjaro works for you include: how your body responds to the GIP and GLP-1 receptor agonist mechanism, your adherence to a reduced-calorie diet, your activity level, your genetics, your age, and any underlying health conditions like type 2 diabetes. Mounjaro is a prescription-only medicine available in the UK following clinical assessment—it is not assured to produce significant weight loss in every person.
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.
Why Some People See Better Results Than Others
Weight loss with Mounjaro depends partly on factors beyond the medication itself. People who combine the tirzepatide injection with consistent dietary changes, increased physical activity, and good sleep typically see better outcomes than those who rely on the medication alone. Your starting weight also matters—someone with more weight to lose may see larger absolute numbers but potentially similar percentage losses.
Individual differences in metabolism, insulin sensitivity, and how your body responds to appetite-suppressing signals all influence results. Some people's bodies simply respond more effectively to GLP-1 and GIP activation than others. Your prescriber will monitor your progress and may adjust your Mounjaro dose titration schedule or suggest lifestyle modifications if you are not seeing expected results after several weeks.
- 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.
Does Mounjaro work immediately?
No. Mounjaro takes time to build up in your system. Most people notice changes in appetite within 2–4 weeks, but significant weight loss typically takes 8–12 weeks to become apparent. The medication works best over months, not days.
What percentage of people lose weight on Mounjaro?
Clinical trials showed that the vast majority of participants lost weight, but the amount varied dramatically. Some lost over 25% of body weight, whilst others lost 5–10%. Individual response is highly variable, which is why results cannot be assured.
Can I use our GLP-1 weight loss calculator to estimate my results with Mounjaro?
Yes. Our free weight loss calculator on this page uses clinical trial data to show potential weight loss ranges at different doses. This gives you a realistic estimate based on evidence, though your actual results may differ from the projection.
What if Mounjaro does not work for me after 3 months?
Discuss with your prescriber. They may increase your dose (you may not yet be at the optimal dose for your body), suggest dietary or activity changes, or consider alternative weight management options. Not every medication works equally for every person.
Is Mounjaro more effective than Wegovy?
Clinical trials suggest Mounjaro (tirzepatide) may produce slightly larger average weight loss than Wegovy (semaglutide) because it activates two pathways instead of one. However, individual variation is large—some people respond better to Wegovy. Your prescriber will advise which is suitable 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.