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
When Can You See Weight Loss with UK Medication?
Weight loss timelines vary significantly depending on your starting weight, metabolism, and whether you're using prescription medication. With UK-licensed options like Mounjaro and Wegovy, most people begin noticing changes within 4โ8 weeks, though some see results sooner. This guide explains realistic expectations for prescription weight management in the UK, NHS eligibility, and how to track your progress alongside lifestyle changes.
10,000+ calculations today ยท NHS-aligned thresholds ยท 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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
UK-Licensed Weight Loss Medications and Timeline
Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only GLP-1 medications licensed in the UK for weight management. Clinical trials show that most people experience noticeable weight loss between weeks 4 and 12 of treatment, with average weight loss around 15โ21% of body weight over 72 weeks for Mounjaro and approximately 15% for Wegovy when used alongside a reduced-calorie diet and increased physical activity.
- Weeks 1โ4: Appetite suppression begins; some feel fuller sooner but weight change may be minimal
- Weeks 4โ12: Most people start seeing measurable weight loss on the scales and in clothes fit
- Weeks 12+: Progressive weight loss continues as doses are optimised
Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses. Individual results vary significantly โ your GP or prescriber can discuss realistic expectations based on your personal health.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
NHS Access vs Private: Getting Started with Prescription Weight Loss
In the UK, prescription weight loss medication is available through two routes. NHS access is via specialist tier 3 weight management services (referral from your GP) โ availability and waiting times vary significantly by region. Private access is through GPhC-registered online prescribing following a clinical assessment, with no NHS referral needed.
To find out if you're eligible, check your BMI using our free BMI calculator. Prescription weight management is typically available for adults with a BMI of 30 or above, or 27โ29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea). Your GP can advise on NHS eligibility and referral, or you can pursue private assessment options. Track your weight loss journey with our free progress tracker once you start.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 quickly will I see weight loss with Mounjaro or Wegovy?
Most people notice weight loss between weeks 4 and 12, though some see changes sooner. Measurable results typically appear within 8โ12 weeks when combined with a reduced-calorie diet and increased physical activity. Individual results vary based on starting weight, metabolism, dose, and adherence to lifestyle changes.
Can I use our BMI calculator to check if I'm eligible for prescription weight loss medication?
Yes, use our free BMI calculator to determine your current BMI. If it's 30 or above, or 27โ29.9 with weight-related health conditions, you may be eligible. However, a prescriber must assess your individual health before offering medication โ BMI alone isn't the only factor considered.
What's the difference between NHS and private weight loss medication access in the UK?
NHS access is through specialist weight management services by GP referral, with availability varying by region and potential waiting lists. Private access is through online prescribing with GPhC-registered pharmacies, available without NHS referral but at a cost. Both require a clinical assessment and prescription from a licensed UK prescriber.
Will I lose weight if I don't change my diet or exercise alongside medication?
Prescription weight loss medications are designed to work alongside reduced-calorie diet and increased physical activity โ not instead of them. Clinical trials show that weight loss results are achieved through the combination of medication, dietary change, and lifestyle modifications. Your prescriber will discuss this during assessment.
How can I track my weight loss progress once I start medication?
Use our free progress tracker to log your weight, measurements, and progress regularly. Tracking helps you see changes beyond the scales โ such as improved energy, better sleep, or clothes fitting differently โ which are often noticed before significant weight loss appears on the scale.
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.