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 Much Weight Loss Per Week With Mounjaro?
Mounjaro (tirzepatide) is a prescription-only once-weekly injection that may help support weight loss in UK adults. Clinical trials showed that people taking Mounjaro lost an average of 0.5 to 1 kg per week on higher doses, though individual results vary considerably. Weight loss isn't immediate — most people see meaningful changes after 4 to 8 weeks. The NHS and NICE have approved tirzepatide for specialist weight management services in England. This guide explains real weekly weight loss data, NHS eligibility, and what clinical evidence tells us about realistic expectations.
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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.
Weekly Weight Loss Data From Clinical Trials
The SURMOUNT-1 trial (the main UK-referenced study) tracked weight loss over 72 weeks in adults taking Mounjaro at different doses. Here's what the data showed:
- 5 mg dose: average weight loss of approximately 15% body weight over 72 weeks (roughly 0.3–0.4 kg per week)
- 10 mg dose: approximately clinically studied weight loss (roughly 0.5–0.7 kg per week)
- 15 mg dose: approximately clinically studied weight loss (roughly 0.5–0.8 kg per week)
However, these are averages — some people lost more, others less. Weight loss typically accelerates after the first 4 weeks as the body adjusts to the medication. Most weight loss occurs in weeks 4 to 16. After week 16, weight loss often slows or plateaus, which is normal. Importantly, all trial participants also followed a reduced-calorie diet and increased physical activity — Mounjaro works best alongside lifestyle changes, not instead of them.
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.
NHS Eligibility and UK Prescribing Context
In the NHS, Mounjaro (tirzepatide) is available through tier 3 specialist weight management services, not standard GP prescription. To access it on the NHS, you typically need referral from your GP to a specialist service in your Integrated Care Board (ICB) area. NICE guidance recommends tirzepatide for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (27.5 and above) due to higher cardiovascular risk at the same BMI. NHS waiting lists for specialist services vary significantly by region — some areas have waits of several months. Our free GLP-1 weight loss calculator can help you understand projected outcomes at different doses.
- 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.
Is 0.5 kg weight loss per week realistic with Mounjaro?
Yes, but only on higher doses (10–15 mg) and alongside a reduced-calorie diet and exercise. Lower doses (5 mg) typically result in slower weight loss of 0.3–0.4 kg per week. Clinical trial data showed these averages, but individual results vary. Some people lose faster, others more slowly. Consistency with diet and physical activity is essential.
When does weight loss start with Mounjaro?
Most people notice initial appetite suppression and small weight changes within 2–4 weeks. However, meaningful weight loss (1–2 kg) usually becomes apparent after 4–8 weeks as the dose builds up. Remember, Mounjaro requires dose escalation over 20 weeks to reach maximum effect, so patience is important during the early stages.
How do I access Mounjaro through the NHS?
Ask your GP for referral to your local tier 3 specialist weight management service. You'll need a BMI of 30 or above, or 27–29.9 with a weight-related health condition. NHS availability and waiting times vary by region. If NHS waiting lists are lengthy, private online prescribing is available through UK-licensed prescribers and GPhC-registered pharmacies.
Does weight loss continue indefinitely with Mounjaro?
No. Clinical trials showed that weight loss typically plateaus after 12–16 weeks once you reach your maintenance dose. This is normal and expected. Long-term weight loss is maintained through continued medication use alongside diet and exercise. If you stop Mounjaro, weight is often regained gradually.
How does Mounjaro weight loss compare to Wegovy?
In clinical trials, Mounjaro (tirzepatide) showed slightly higher average weight loss (20.9% at 15 mg) compared to Wegovy (semaglutide) at approximately 15% body weight. However, this represents average data — individual responses vary. Mounjaro is a dual GIP/GLP-1 receptor agonist, while Wegovy is GLP-1 only. Your prescriber will recommend the most suitable option based on your individual health profile.
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.