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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How Much Mounjaro for Weight Loss
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK, but the amount you need depends entirely on your individual health profile, current weight, and how your body responds to the medication. There's no single "right" dose for everyone — treatment starts low and increases gradually over several months. Clinical trials showed that doses ranging from 5mg to 15mg helped people lose between 15% and 21% of their body weight on average, though results vary significantly. Your GP or prescriber will assess what's appropriate for you following a clinical consultation.
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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.
Mounjaro Dosing Schedule and Expected Weight Loss
Mounjaro is prescribed in a step-up dosing schedule, starting at 2.5mg per week and increasing every 4 weeks up to a maximum of 15mg. Each dose is injected once weekly.
- Weeks 1–4: 2.5mg (starting dose for adjustment)
- Weeks 5–8: 5mg (first maintenance dose)
- Weeks 9–12: 7.5mg (escalation if needed)
- Weeks 13–16: 10mg (further escalation)
- Weeks 17–20: 12.5mg (high dose)
- Week 21+: 15mg (maximum dose)
In the SURMOUNT clinical trials, participants at 15mg lost approximately 21% of their body weight after 72 weeks, whilst those on 5mg lost around 15%. However, you may reach your ideal weight or healthy weight for your height before reaching the maximum dose — your prescriber will monitor your progress and may adjust accordingly. Weight loss typically becomes most noticeable between weeks 8–12 as doses increase. Try our GLP-1 weight loss calculator to estimate potential results at different doses based on your starting weight.
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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.
Individual Factors That Affect How Much Weight You'll Lose
Weight loss on Mounjaro is not the same for everyone. Your results depend on several factors beyond the dose itself: your starting weight, age, metabolism, how strictly you follow a reduced-calorie diet, how much physical activity you do, whether you're taking other medications, and your genetic predisposition to weight loss. Some people reach a healthy weight range (BMI 18.5–24.9 according to NHS guidelines) at lower doses; others require the full 15mg to achieve meaningful results. Ethnicity also matters — if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, you may have different health thresholds and weight loss targets. Check your healthy weight for your height using our free BMI calculator, then discuss realistic targets with your prescriber.
- 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's the average weight loss with Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, depending on dose. At 5mg, people lost approximately 15%; at 15mg, approximately 21%. However, individual results vary significantly based on diet, exercise, starting weight, and personal factors. Your own results may be higher or lower.
Do you need to reach the maximum 15mg dose?
No. Some people reach their target healthy weight at lower doses like 5mg, 7.5mg, or 10mg. Your prescriber will monitor your progress and may adjust your dose or maintain you at a level that works for you. The maximum dose isn't necessary for everyone.
How long does it take to see weight loss results?
Most people notice changes between weeks 8–12 as doses increase, though some see results earlier. Significant weight loss typically becomes more obvious after 16–20 weeks of treatment. Results depend on dose, diet adherence, and individual metabolism.
Does Mounjaro work better than other weight loss injections?
Mounjaro uses a dual GIP and GLP-1 mechanism, whilst other licensed injections use GLP-1 alone. Clinical data suggests Mounjaro may produce slightly higher average weight loss, but individual responses vary. Your prescriber can advise which is most appropriate for you.
Can you stop Mounjaro once you reach a healthy weight?
This depends on your prescriber's guidance. Some people maintain weight loss after stopping; others regain weight. Discuss your long-term plan with your GP or specialist — many people continue treatment to prevent weight regain, especially if lifestyle alone isn't maintaining results.
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.