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
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Weight Loss Goal Estimator for UK Adults
Setting realistic weight loss goals is essential for long-term success. If you're considering prescription weight management in the UK, understanding what's available, how these medications work, and whether you're eligible can help you make informed decisions with your GP. This guide covers the prescription options available on the NHS and privately, clinical evidence on potential weight loss, and how to estimate what realistic goals might look like for your situation.
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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-Licensed Prescription Weight Management Options
Three prescription medications are currently licensed in the UK for weight management in adults: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy and Saxenda are GLP-1 agonists. Clinical trial data shows average weight loss of 15–21% body weight with Mounjaro and approximately 15% with Wegovy when used alongside a reduced-calorie diet and increased physical activity. Saxenda, a daily injection, typically results in 5–clinically studied weight loss. Eligibility generally requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. These are prescription-only medicines requiring clinical assessment before being prescribed.
Our GLP-1 weight loss calculator can help you estimate potential weight loss at different doses based on your starting weight and the clinical evidence available.
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 Access vs Private Prescription — Finding Out If You're Eligible
In the UK, prescription weight management is available through two routes. NHS access is through specialist tier 3 and tier 4 weight management services, typically requiring a GP referral. Availability varies significantly by region and waiting lists can be lengthy. Private access is available through GPhC-registered online prescribing services following a clinical assessment with a UK-licensed prescriber. The first step is always to speak with your GP about your weight loss goals and health concerns. Your GP can discuss what's appropriate for your situation, refer you to specialist services if eligible, or advise on private options. Use our free BMI calculator to understand your current BMI category and use that as a starting point for the conversation. Setting realistic weight loss goals—typically 5–10% of body weight as a first target—can have significant health benefits regardless of which route you choose.
- 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 much weight can I expect to lose with prescription weight management medication?
Individual results vary considerably. Clinical trials show average weight loss of 15–21% body weight with Mounjaro, around 15% with Wegovy, and 5–10% with Saxenda. These are averages alongside reduced-calorie diet and physical activity. Your GP or prescriber can discuss realistic expectations for your personal situation.
Am I eligible for prescription weight loss medication on the NHS?
Generally, you may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Lower thresholds apply for some ethnic backgrounds. Speak with your GP, who can assess your eligibility and refer you to specialist services if appropriate.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a maximum dose of 15 mg weekly, whilst Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4 mg weekly. Clinical trial data suggests slightly higher average weight loss with Mounjaro, but both are effective. Your prescriber can advise which is most suitable for you.
Can I get prescription weight loss medication privately if I'm not eligible for the NHS?
Yes. Private prescribing is available through GPhC-registered online services. You'll need to complete a clinical assessment with a UK-licensed prescriber. This pathway doesn't require NHS referral, though it does involve costs. Always ensure you're using a legitimate, regulated service.
Should I use a weight loss calculator before speaking to my GP?
Yes. Using our free BMI calculator and weight loss goal estimator can help you understand your starting point and realistic targets. This makes the conversation with your GP more informed and practical. Write down your goals beforehand to help guide the discussion.
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.