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 Weight Loss on Mounjaro 2.5 mg
Mounjaro 2.5 mg is the starting dose of tirzepatide prescribed in the UK for weight management. Whilst 2.5 mg is an adjustment dose, clinical trial data and real-world experience suggest that participants may lose an average of 3–5% of their body weight during the initial 4–8 weeks on this dose. However, weight loss at the 2.5 mg starting dose is typically modest compared to higher maintenance doses. Individual results vary significantly based on adherence to dietary changes, physical activity, and personal metabolism. Always consult your GP or prescriber about realistic expectations for your specific situation.
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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 and Starting Dose Outcomes
Mounjaro 2.5 mg is not a maintenance dose — it's a starting/adjustment dose used for the first 4 weeks of treatment. Based on the SURMOUNT clinical trials, participants at the 2.5 mg dose level showed modest weight loss results compared to the full maintenance doses (5 mg, 10 mg, 15 mg). At 2.5 mg, average weight loss was approximately 3–5% of body weight in the early weeks, though this varies considerably between individuals.
It's important to remember that the full weight loss benefits of tirzepatide appear as doses are escalated over weeks 5–21. The 2.5 mg starting dose is designed to allow your body to adjust to the medication and minimise initial side effects like nausea. Most prescribers increase the dose every 4 weeks if tolerated, with maintenance doses typically at 5 mg or higher. Weight loss continues to increase as the dose increases, with the maximum dose (15 mg) showing approximately 20–21% average body weight loss in clinical trials.
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 Individual Weight Loss Results
Weight loss on any Mounjaro dose — including the 2.5 mg starting dose — depends on several factors beyond the medication itself. Calorie deficit is critical: Mounjaro reduces appetite, but sustainable weight loss still requires eating fewer calories than you burn. Adherence to a reduced-calorie diet and increased physical activity significantly impact outcomes. Personal metabolism, age, baseline weight, and genetics all play a role in how quickly weight loss occurs. Muscle mass and frame size also influence results — two people of the same height and weight may lose weight at different rates depending on their body composition.
Additionally, consistency with injection timing, management of side effects, and how your body responds to the GIP/GLP-1 mechanism all matter. Your GP or prescriber can use our free BMI calculator and healthy weight range guidance to set realistic goals for your individual circumstances. Track your progress using our free weight loss progress tracker to monitor results beyond just the number on the scales.
- 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 should I expect to lose on Mounjaro 2.5 mg?
At 2.5 mg (the starting dose), average weight loss is approximately 3–5% of body weight during the first 4 weeks. This is modest compared to higher doses because 2.5 mg is an adjustment dose, not a maintenance dose. Individual results vary significantly based on diet, exercise, and personal metabolism. Your prescriber can discuss realistic expectations for you specifically.
Why is Mounjaro 2.5 mg only a starting dose?
Mounjaro 2.5 mg allows your body to adjust to the medication and typically causes fewer side effects like nausea. Most prescribers increase the dose every 4 weeks if tolerated. Weight loss generally increases as the dose increases, with maintenance doses typically at 5 mg or higher, reaching up to 15 mg as the maximum.
What's the difference between 2.5 mg and higher Mounjaro doses for weight loss?
At 2.5 mg, average weight loss is 3–5% of body weight. At 5 mg, approximately 15% of body weight. At 10 mg, approximately 19.5%. At 15 mg (maximum), approximately 20–21% of body weight. These are clinical trial averages; individual results vary based on adherence to lifestyle changes and personal response.
Does the NHS provide Mounjaro 2.5 mg for weight loss?
Mounjaro is available through NHS specialist weight management services (tier 3/4) for eligible adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Access varies by region and waiting times can be long. Private prescribing is also available following an online clinical assessment.
How can I track my weight loss progress on Mounjaro?
Use our free weight loss progress tracker to log your weight, measurements, and how you feel week to week. Our BMI calculator helps you understand your current weight status and healthy weight range for your height. Remember that weight loss isn't linear — some weeks you'll see changes, others you won't, and that's normal.
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.