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 Semaglutide Works for Weight Loss
Semaglutide is a prescription-only GLP-1 receptor agonist medication licensed in the UK for weight management under the brand name Wegovy. It may help reduce appetite and support weight loss when combined with lifestyle changes. Clinical trials showed that adults using semaglutide lost an average of around 15% of their body weight, though individual results vary significantly. Understanding how this weekly weight loss injection works, who is eligible, and what to expect can help you make an informed decision about whether it might be right for you.
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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 Semaglutide Works and Expected Results
Semaglutide is a GLP-1 receptor agonist — it mimics a natural gut hormone that regulates appetite and blood sugar. When you take this weekly weight loss injection, it may help you feel fuller after eating smaller meals, reduce food cravings, and slow how quickly food leaves your stomach. This mechanism differs from older weight loss approaches and is based on how your body's natural appetite signals work.
In the STEP clinical trials conducted by Novo Nordisk, adults taking semaglutide 2.4mg (the maximum dose) lost an average of 14.9% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. However, results vary — some people lost more, some less. Weight loss typically begins within the first few weeks but continues gradually over months. Using our GLP-1 weight loss calculator can help you estimate potential outcomes at different dose levels based on trial data.
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.
UK Eligibility and How to Access Semaglutide
In the UK, semaglutide (Wegovy) may be prescribed to adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to increased health risks at lower weights.
Access is available through NHS specialist weight management services (though availability and waiting times vary significantly by region) or through private online prescribing following a clinical assessment with a UK-licensed prescriber. A GP or prescriber will assess your individual health to determine if semaglutide is suitable. Check your BMI using our free BMI calculator to see if you might meet initial eligibility criteria.
- 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 semaglutide the same as Ozempic?
Both Ozempic and Wegovy contain semaglutide, but they are different products. Ozempic is licensed for type 2 diabetes management and contains up to 2mg. Wegovy is the licensed weight management version, containing up to 2.4mg per dose. In the UK, Wegovy is the prescription-only medication approved for weight loss.
How much weight can I expect to lose with semaglutide?
Clinical trials showed an average of clinically studied weight loss at the maximum dose (2.4mg), but individual results vary significantly. Some people lose more, some less. Weight loss depends on your starting weight, lifestyle changes, and individual response. Results are never assured — always use conditional language like "may help."
What are the common side effects of semaglutide?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — especially when starting or increasing doses. These often improve over time. Less common side effects include headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain. Always discuss side effects with your prescriber.
How often do I inject semaglutide?
Semaglutide (Wegovy) is a once-weekly injection. You inject the same day each week using a pre-filled auto-injection pen. Doses range from 0.25mg in week 1 up to 2.4mg, increasing gradually every 4 weeks. Each pen contains 4 weekly doses, so you need a new pen every month.
Can I get semaglutide on the NHS?
Semaglutide may be available through NHS specialist weight management services (tier 3), but availability varies significantly by region and waiting times can be very long. Access through the NHS requires referral from your GP to a specialist service in your area. Private online prescribing is also available following a clinical assessment with a UK-licensed prescriber.
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.