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 Long Do You Need To Be On Mounjaro?
There's no fixed timeframe for how long you need to take Mounjaro (tirzepatide) — treatment duration depends on your individual health goals, response to the medication, and guidance from your prescriber. Most people continue for at least 12 months if the medication is working, though some may stay on it longer. Unlike some short-term treatments, Mounjaro is typically viewed as a longer-term support tool alongside lifestyle changes. Your GP or prescriber will review your progress regularly to decide whether to continue, adjust your dose, or eventually reduce the medication.
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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 vs Wegovy: Treatment Duration and Clinical Evidence
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are ongoing treatments rather than short courses. In the SURMOUNT clinical trials, participants using Mounjaro continued for 72 weeks (approximately 17 months) and experienced progressive weight loss, with results showing that the dual GIP and GLP-1 mechanism supported sustained reduction in appetite. Similarly, Wegovy participants in the STEP trials continued for 68 weeks and achieved weight loss averaging around 14.9% of body weight.
The key difference: once you stop either medication, the appetite-suppressing effects gradually reduce, meaning weight can return. Neither medication is typically a "course" you complete — they're ongoing medications you take as long as they're working and your prescriber recommends them. Your UK prescription will specify a review schedule, often every 3–6 months, to assess whether to continue. Use our GLP-1 weight loss calculator to explore potential outcomes over different timescales and understand what sustained treatment might achieve for you.
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.
Individual Suitability and Prescriber Decision
How long you should be on Mounjaro is a decision made between you and your UK prescriber based on your individual circumstances — there is no universal answer. Factors include whether you're losing weight steadily, tolerating the medication well, achieving your health goals, and whether weight-related conditions (like type 2 diabetes or high blood pressure) are improving.
Some people may take Mounjaro for a year or two, others longer. Your prescriber might eventually suggest stopping to see if you can maintain weight loss with lifestyle changes alone. Equally, they might recommend continuing if you've found your weight creeps back up without it. For eligible adults in the UK with a BMI over 27 and weight-related health conditions, or BMI over 30, a prescriber will assess whether treatment is appropriate and discuss realistic timescales.
- 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.
Do you have to stay on Mounjaro forever?
No. Treatment duration is individualised. Many people take it for 12–24 months or longer, but you don't have to take it indefinitely. Your prescriber will review your progress every 3–6 months and discuss whether to continue, adjust, or stop based on your weight loss, health improvements, and tolerability. Some people stop and maintain weight loss; others find they need ongoing support.
What happens when you stop taking Mounjaro?
The appetite-suppressing effects gradually reduce over weeks. Weight can return if you don't maintain the lifestyle changes (reduced calories and increased activity) that supported your initial loss. This is why Mounjaro is typically combined with diet and exercise. Your prescriber may recommend a gradual dose reduction rather than stopping suddenly, and will advise you on managing the transition.
Is Mounjaro treatment duration different from Wegovy?
Both are ongoing treatments with no fixed end date — duration is individualised for each patient. Clinical trials ran Mounjaro for 72 weeks and Wegovy for 68 weeks. Neither has a standard "course length". The choice between them depends on your eligibility, prescriber preference, and how your body responds, not on treatment length.
How often will my prescriber review my Mounjaro treatment?
UK prescribers typically review GLP-1 medications every 3–6 months. They'll assess your weight loss, side effects, blood sugar control (if diabetic), and overall health. These reviews help determine whether to continue at your current dose, increase, decrease, or eventually stop treatment.
Can I use our BMI calculator alongside Mounjaro treatment?
Yes. Track your BMI regularly with our free BMI calculator throughout your treatment to monitor progress objectively. Calculate it at baseline, then monthly or every 3 months to see changes. This helps you and your prescriber assess whether the medication is working and whether your BMI is moving towards a healthier range for your height.
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.