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 Do People Lose On Mounjaro?
Clinical trials show that people taking Mounjaro (tirzepatide) lose an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Weight loss depends on the dose, adherence to a reduced-calorie diet, physical activity levels, and personal metabolism. In the UK, Mounjaro is prescribed through NHS specialist services or private online prescribing following clinical assessment. This guide explains what NHS data and clinical evidence tell us about realistic weight loss expectations.
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.
Mounjaro Weight Loss Results — Clinical Evidence and NHS Context
The SURMOUNT-1 clinical trial provides the most robust data on Mounjaro weight loss in the UK. Results showed:
- 5 mg dose: average weight loss of approximately 15% body weight (72 weeks)
- 10 mg dose: average weight loss of approximately 19.5% body weight
- 15 mg dose: average weight loss of approximately 20.9% body weight (maximum dose)
These results were achieved alongside a reduced-calorie diet and increased physical activity. Weight loss typically begins within the first 4 weeks, with most significant changes occurring between weeks 8–24. It's crucial to remember that these are clinical trial averages — individual weight loss varies considerably based on dose titration, how your body responds, diet adherence, and exercise consistency. The NHS now recognises Mounjaro as an approved weight management option through specialist tier 3 services, though regional availability and waiting lists vary significantly across ICBs.
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.
Realistic Weight Loss Expectations — What the Data Shows
For a 100 kg person on the maximum 15 mg Mounjaro dose, clinical data suggests potential weight loss of approximately 20–21 kg over 72 weeks — but this is an average, not a assures. Some people lose more, some lose less. Weight loss typically plateaus if lifestyle factors aren't maintained. Using our free GLP-1 weight loss calculator, you can estimate potential outcomes at different doses based on clinical trial data. It's also worth checking your current BMI using our BMI calculator to understand where you start and set realistic health-focused targets. Many people find that even modest weight loss (5–10%) delivers meaningful health improvements including better blood pressure control and improved blood sugar levels.
- 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 will I lose on Mounjaro in the first month?
Most people begin seeing weight loss within the first 4 weeks, though this is typically modest (1–2 kg). Significant weight loss accelerates between weeks 8–16 as you reach higher maintenance doses. Individual results depend heavily on diet adherence and activity levels — Mounjaro works alongside lifestyle changes, not instead of them.
Is Mounjaro weight loss permanent after stopping the medication?
Clinical data shows that weight loss is often regained after stopping Mounjaro if lifestyle changes aren't maintained. Long-term weight management requires ongoing dietary and exercise habits. Many people stay on Mounjaro long-term to sustain results, though this requires ongoing prescription and clinical monitoring.
How does Mounjaro weight loss compare to Wegovy in the UK?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist, while Wegovy (semaglutide) is a single GLP-1 agonist. SURMOUNT trials show Mounjaro produces slightly higher average weight loss (~20.9% at 15 mg) compared to Wegovy's STEP trial data (~14.9% at 2.4 mg). However, individual responses vary — both are effective, and prescriber choice depends on clinical suitability.
Can I get Mounjaro on the NHS in the UK?
Yes — Mounjaro is now approved by NICE for NHS use through specialist tier 3 weight management services. Access varies by region, with some areas having significant waiting lists. You'll need referral from your GP and assessment by a specialist team. Private online prescribing offers faster access if you meet eligibility criteria.
What affects how much weight I lose on Mounjaro?
Key factors include: dose level (higher doses typically produce more loss), diet adherence (essential for results), physical activity levels, baseline weight, metabolism, how your body responds to tirzepatide, and consistency with injections. Your GP or prescriber can discuss which factors may influence your individual outcome.
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.