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
What Happens to Your Face After 20 Lb Weight Loss?
When you lose 20 pounds (approximately 9 kg), visible changes often appear in your face first. Fat deposits under the chin, cheeks, and jawline diminish, making facial features more defined. For sustainable weight management in the UK, prescription options like Mounjaro and Wegovy are available through NHS weight loss services or private clinical assessment. These medications support steady, healthy weight loss alongside diet and exercise — helping you achieve lasting results with visible improvements.
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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.
UK Prescription Weight Loss Options for Sustainable Results
Losing 20 lbs typically results in noticeable facial changes — reduced puffiness, sharper cheekbones, and a more defined jawline. For eligible UK adults, prescription weight management medication can support consistent, healthy weight loss. Three main options are licensed in the UK:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once-weekly injection. Clinical trials showed average weight loss of 15–21% of body weight.
- Wegovy (semaglutide) — GLP-1 receptor agonist, once-weekly injection. Average weight loss of approximately 15% of body weight in clinical trials.
- Saxenda (liraglutide) — GLP-1 receptor agonist, daily injection. Lower dose than Mounjaro and Wegovy but proven effective.
All three are prescription-only and require clinical assessment. Eligibility includes adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. Use our free GLP-1 weight loss calculator to explore potential results at different doses.
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.
How to Access Weight Loss Medication in the UK
Two main pathways exist for prescription weight management in the UK. NHS access is through specialist tier 3 weight management services — you'll need a GP referral, though waiting times vary significantly by region. Private access is available through GPhC-registered online prescribers following an online clinical assessment, without NHS referral.
Your GP can assess your eligibility based on your BMI and health history. You can also use our free BMI calculator to check where you currently stand. Whether you lose weight through medication, lifestyle changes, or both, sustainable loss (0.5–1 kg per week) leads to the most lasting facial and overall health improvements. Always discuss your weight management goals with your GP or a qualified healthcare professional.
- 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 quickly will my face change after weight loss?
Facial changes are often visible within 4–8 weeks of consistent weight loss, particularly in the cheeks, chin, and jawline. However, individual timelines vary. Sustainable loss of 0.5–1 kg per week (the NHS-recommended rate) typically produces noticeable facial definition within 2–3 months.
Will prescription weight loss medication help me lose 20 lbs?
Prescription GLP-1 medications like Mounjaro and Wegovy are designed to support significant weight loss — clinical trials showed average losses of 15–21% of body weight. A 20 lb loss falls well within typical results for eligible adults, especially when combined with dietary changes and physical activity.
Am I eligible for NHS weight loss medication?
You may be eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea, or cardiovascular disease). Check your BMI using our free calculator, then discuss eligibility with your GP.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) works on two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) targets one (GLP-1 only). Both are once-weekly injections. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. Your prescriber will recommend the most suitable option for you.
Can I combine weight loss medication with diet and exercise?
Yes — prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. They support appetite control and consistency, making it easier to maintain healthy habits. Track your progress with our free progress tracker to monitor weight changes and facial improvements over time.
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.