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
Does Wegovy Work? What the Clinical Evidence Shows
Yes, Wegovy does work for weight loss in clinical trials — but results vary significantly between individuals. Based on the STEP-1 trial data, adults taking semaglutide (Wegovy) lost an average of approximately 15% of their body weight over 68 weeks when combined with a reduced-calorie diet and increased physical activity. However, not everyone experiences the same results. Some people lose more, others less. Wegovy is a prescription-only GLP-1 receptor agonist licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Whether it's right for you depends on individual factors, medical history, and prescriber assessment.
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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.
How Wegovy Works: Mechanism and Clinical Trial Results
Wegovy (semaglutide) is a GLP-1 receptor agonist — it mimics a natural hormone that signals fullness to the brain, reduces appetite, and slows how quickly food leaves the stomach. In the STEP-1 clinical trial, participants taking the maximum dose of 2.4 mg lost an average of 14.9% of their body weight. This is significant compared to placebo (which resulted in approximately 2.4% loss), but individual results ranged widely.
- Average weight loss on Wegovy 2.4 mg: ~15% body weight
- Timeframe: 68 weeks (approximately 16 months)
- Requires: reduced-calorie diet and physical activity
- Mechanism: GLP-1 receptor agonist (single pathway)
Importantly, the STEP trials showed that weight loss plateaus after approximately 12 months — this is normal. Results depend on dose adherence, lifestyle changes, and individual metabolism. Some people stop losing weight on Wegovy; others maintain their loss long-term.
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.
Wegovy vs Mounjaro: Key Differences in Effectiveness
Mounjaro (tirzepatide) and Wegovy differ in mechanism and average outcomes. Mounjaro activates two pathways (GIP + GLP-1), whilst Wegovy activates only GLP-1. In their respective trials, Mounjaro showed slightly higher average weight loss (15–21% vs Wegovy's 15%), but this doesn't mean Mounjaro is "better" — individual response varies greatly. Some people respond better to Wegovy; others to Mounjaro. Dose also matters: Wegovy's maximum is 2.4 mg weekly, whilst Mounjaro goes up to 15 mg weekly, allowing more personalised titration. Your prescriber will assess which suits your individual health profile, medical history, and previous weight loss attempts.
- 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 Wegovy work for everyone?
No. Whilst clinical trials show average weight loss of 15%, individual results vary significantly. Some people lose more, others lose less or plateau. Approximately 20–30% of trial participants experience minimal weight loss. Success depends on adherence, lifestyle changes, genetics, and individual metabolism. Your GP or prescriber can discuss realistic expectations for you.
How quickly does Wegovy work for weight loss?
Weight loss typically begins within the first 2–4 weeks but accelerates over 12–16 weeks as you reach therapeutic doses. Most significant loss occurs between weeks 12–52. The STEP trials measured results at 68 weeks. Weight loss is gradual (0.5–1 kg per week on average) and requires ongoing use — stopping Wegovy often leads to weight regain.
What's the difference between Wegovy and Mounjaro for weight loss?
Wegovy is a GLP-1 agonist; Mounjaro is a dual GIP+GLP-1 agonist. Mounjaro showed slightly higher average weight loss (15–21% vs 15%), but differences are modest. Both require prescription and clinical assessment. Neither is "superior" — suitability depends on your individual health profile and how your body responds. Your prescriber decides which is appropriate.
Can you use our GLP-1 weight loss calculator to estimate Wegovy results?
Yes. Our free GLP-1 weight loss calculator can help you estimate potential weight loss at different doses based on clinical trial data. Simply enter your current weight and height to see projections. Remember these are averages — your actual results may differ. Always consult your prescriber for personalised advice.
Does Wegovy work without diet and exercise?
No. Wegovy works best alongside a reduced-calorie diet and increased physical activity. Clinical trials specifically required lifestyle changes alongside the medication. Wegovy reduces appetite and supports feeling fuller, but it's not a standalone solution. Diet, exercise, and medication work together for sustainable weight loss.
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.