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
How Mounjaro Helps with Weight Loss
Mounjaro (tirzepatide) is a prescription-only weekly injection that may help with weight loss by activating two natural hormone pathways in your body. Clinical trials showed participants lost an average of 15–21% of their body weight when using Mounjaro alongside a reduced-calorie diet and increased physical activity. Results vary significantly between individuals. Access in the UK is through NHS specialist services or private prescribing following a clinical assessment. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses.
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.
How Mounjaro Works for Weight Loss
Mounjaro is a dual GIP and GLP-1 receptor agonist — this dual mechanism sets it apart from other weight loss injections like Wegovy (semaglutide), which targets GLP-1 only. The medication activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1), which work together to help regulate appetite and reduce food cravings. It signals to your brain that you feel fuller after eating smaller portions, and it slows how quickly food leaves your stomach — though this effect typically reduces over time with continued use.
In the SURMOUNT-1 clinical trial, participants on the maximum dose (15 mg weekly) lost an average of 20.9% of their body weight over 72 weeks alongside lifestyle changes. At the 10 mg dose, average loss was 19.5%. These are average results — individual weight loss varies based on metabolism, adherence, diet, and exercise. Mounjaro is not insulin and works differently from diabetes medications, though it can help improve blood sugar control.
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.
UK Access and Weight Loss Eligibility
In the UK, Mounjaro is available as a prescription-only weekly injection in pre-filled KwikPen devices. You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions including type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. NHS access is through specialist tier 3 weight management services (referral required from your GP), though waiting lists vary significantly by region. Private prescribing is available through licensed online services following an online clinical assessment, without requiring NHS referral.
Use our free BMI calculator to check your starting point, and our progress tracker to monitor weight loss once you begin treatment. Your prescriber will assess suitability and start you on 2.5 mg weekly, increasing gradually to your maintenance dose over 16–20 weeks. Success depends on combining the weekly weight loss injection with sustained dietary changes and regular physical activity.
- 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 clinically studied weight loss?
No. Mounjaro may help support weight loss, but results vary. Clinical trials showed average weight loss of 15–21%, but individual outcomes depend on diet, exercise, metabolism, and adherence. It's not assured — some people lose more, others less. Always combine treatment with lifestyle changes.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Both are once-weekly injections. Clinical trials showed Mounjaro produced slightly higher average weight loss (20.9% at maximum dose) versus Wegovy (14.9%), but individual results vary. Your prescriber will recommend based on your health.
How long does it take to lose weight on Mounjaro?
Weight loss typically becomes noticeable after 4–8 weeks, with most loss occurring over 12–16 weeks as your dose increases. The SURMOUNT trial measured results over 72 weeks (18 months). Mounjaro is not a structured approach — sustainable weight loss develops gradually alongside diet and exercise changes.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for NHS use, but access is through specialist tier 3 weight management services, not standard GP prescription. You need referral from your GP, and availability varies by region — waiting lists can be long. Private access is available through licensed online prescribers.
Will I regain weight if I stop Mounjaro?
Weight regain is possible after stopping any weight loss medication. Clinical data suggests gradual weight regain occurs in the months after stopping. The goal is to use Mounjaro alongside lifestyle changes that become sustainable long-term — your GP can advise on managing weight after treatment ends.
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.