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 lose an average of 15% to 21% of their body weight, though individual results vary significantly. On the highest dose (15 mg), participants in the SURMOUNT-1 trial lost approximately 20.9% of their body weight over 72 weeks. However, weight loss depends on many personal factors including your starting weight, adherence to the medication, diet, activity level, and individual metabolism. Mounjaro is a prescription-only medicine and works best alongside a reduced-calorie diet and increased physical activity. Results are not assured, and some people lose more weight than others.
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.
Average Weight Loss From Clinical Trials
In the SURMOUNT-1 clinical trial, adults taking Mounjaro (tirzepatide) achieved the following average weight losses over 72 weeks alongside a reduced-calorie diet and exercise:
- 5 mg dose: Approximately 15% of body weight
- 10 mg dose: Approximately 19.5% of body weight
- 15 mg dose: Approximately 20.9% of body weight (highest dose)
To put this in context, a person starting at 100 kg could expect to lose roughly 15–21 kg at the highest dose. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses based on your starting weight. It's important to remember these are average figures—some people lose more, some less. Weight loss typically develops gradually over 16–20 weeks as doses increase, with continued loss over the full treatment period.
Clinically BackedWeight Loss
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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.
What Affects How Much Weight You Lose
Individual weight loss on Mounjaro depends on several personal factors beyond the medication itself. Your starting weight and BMI influence outcomes—people with higher starting weights often lose more total weight. Diet adherence is critical; Mounjaro reduces appetite but only works if you eat fewer calories. Your physical activity level, metabolism, age, and genetics all play a role. Some people experience faster weight loss in the first 8–12 weeks, then plateau. Medical conditions like thyroid disease or PCOS, plus certain medications, may affect results. Importantly, body composition matters—the scale doesn't show whether you're losing fat or muscle. Use our free BMI calculator to track your healthy weight range for your height, and monitor progress beyond just the number on the scales.
- 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 15–clinically studied weight loss assured on Mounjaro?
No. Clinical trials show these are average results, but individual outcomes vary. Some people lose more, others less, depending on diet, activity, adherence, and personal metabolism. Your GP or prescriber can discuss what to realistically expect based on your circumstances.
How long does it take to see weight loss on Mounjaro?
Weight loss typically begins after 4–8 weeks as doses increase. Noticeable results often appear by weeks 12–16. Most weight loss in trials occurred between weeks 16–72. Consistency with diet and exercise is key to maximising results.
Can someone lose more than 21% of their body weight on Mounjaro?
Yes, some people lose more than the trial average, especially those who combine the medication with significant dietary changes and regular activity. However, results above 21% are less common and should not be expected or assured.
Does weight loss continue after stopping Mounjaro?
No. Most people regain weight after stopping Mounjaro unless lifestyle changes (diet and exercise) are maintained long-term. This is why Mounjaro is often described as a tool to support lasting behaviour change, not a permanent solution.
How does my healthy weight range compare to Mounjaro weight loss?
Your healthy weight depends on your height and is measured by BMI (18.5–24.9). Use our free weight loss calculator and BMI calculator to estimate your personal healthy weight range, then discuss realistic targets with your GP before starting any weight loss treatment.
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.