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
Largest Weight Loss Ever — What's Possible in the UK
The largest weight losses ever recorded often involve intensive medical support, structured lifestyle changes, and prescription weight management medication. In the UK, adults struggling with significant excess weight now have access to clinically-proven options including Mounjaro and Wegovy — prescription medications that can support meaningful weight reduction when combined with diet and exercise. Understanding what's realistic, how these medications work, and whether you're eligible is the first step towards sustainable weight management.
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.
UK-Licensed Weight Management Medications
The UK now has three main prescription weight loss medications licensed for eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks when combined with reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a daily GLP-1 injection. Average weight loss around 5–8% of body weight in trials.
All three are prescription-only medicines requiring a clinical assessment. Individual results vary significantly based on dosage, adherence, diet, and physical activity. Our GLP-1 weight loss calculator can help you estimate potential results at different medication 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.
NHS vs Private Access and Eligibility
In the UK, weight loss medications are available through both NHS specialist services and private prescribing. NHS access: Referral to a tier 3 or 4 specialist weight management service through your GP. Availability varies by region, and waiting lists can be lengthy. Private access: Online consultation with a UK-licensed prescriber, available without NHS referral. To be eligible for any prescription weight management medication, you typically need 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 sleep apnoea. Use our BMI calculator to check your current status, and speak to your GP about options for weight management support in your area.
- 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.
What's the largest weight loss possible with prescription medication?
Clinical trials show average weight losses of 15–21% of body weight with Mounjaro and around 15% with Wegovy over 12–18 months. Some individuals lose significantly more, others less. Results depend on dose, adherence, calorie intake, and physical activity. These medications work best alongside lifestyle changes, not as a standalone solution.
How quickly can I expect to lose weight on these medications?
Most people begin to notice weight loss within 4–8 weeks. The NHS recommends a safe rate of 0.5–1 kg per week. With prescription medications alongside diet and exercise, many people achieve this or slightly faster. Your prescriber will monitor progress and adjust dosage as needed.
Am I eligible for weight loss medication on the NHS?
Generally, yes, if you have a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions like diabetes or high blood pressure. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. Ask your GP for a referral to a specialist weight management service to be assessed.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections for weight management. Mounjaro uses a dual mechanism (GIP and GLP-1), while Wegovy uses GLP-1 only. Clinical evidence suggests Mounjaro may produce slightly greater average weight loss, but results vary individually. Your prescriber will recommend the most suitable option based on your health.
Can I lose weight without prescription medication?
Yes. A calorie deficit of around 500 kcal per day typically results in 0.5 kg weight loss per week. The NHS recommends combining dietary changes with increased physical activity. Our free progress tracker can help you monitor your journey. For some people, prescription medication provides additional support when lifestyle changes alone are not sufficient.
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.