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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Stone Weight Loss Calculator — UK Prescription Medication Guide
If you're looking to lose weight and measure progress in stone, understanding UK prescription weight management options can help. For eligible adults, prescription medications like Mounjaro and Wegovy are available through the NHS or privately. This guide explains how UK-licensed weight loss injections work, who qualifies, and how to access them. Use our free GLP-1 weight loss calculator above to estimate potential results, and our BMI calculator to check if you might be eligible for prescription weight management support.
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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-only weight loss medications are licensed in the UK for eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 injection given once weekly. Clinical trials showed participants lost an average of 15–21% of body weight over 72 weeks alongside reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 injection given once weekly. In clinical trials, participants lost approximately 14.9% of body weight at the maximum dose.
- Saxenda (liraglutide) — a GLP-1 injection given daily, with an average weight loss of around 5–10% in clinical trials.
You're typically eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean descent. All three medications work best alongside lifestyle changes, not as replacements for them. Individual results vary significantly.
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 Routes — and Next Steps
In the UK, you can access prescription weight loss medication through the NHS or privately. NHS access involves referral to a tier 3 specialist weight management service (ask your GP). Availability varies by region and waiting lists can be long. Private access is faster — you can consult a UK-licensed prescriber online, and if eligible, receive a prescription from a GPhC-registered pharmacy.
Start by calculating your BMI using our free BMI calculator to see if you fall into an eligible range. Then speak with your GP about your weight management goals. They can assess your overall health, discuss prescription options if suitable, or refer you to specialist services. Use our progress tracker to monitor your weight loss journey in stone and kg once you've begun any weight management programme.
- 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 does the GLP-1 in Mounjaro and Wegovy stand for?
GLP-1 stands for glucagon-like peptide-1, a natural hormone that regulates appetite and blood sugar. Mounjaro is a dual GIP and GLP-1 agonist (it activates two pathways), while Wegovy is a single GLP-1 agonist. Both help reduce hunger and support feeling fuller after smaller meals, making it easier to maintain a calorie deficit for weight loss.
Can I get Mounjaro or Wegovy on the NHS?
Yes, both medications are available through NHS specialist weight management services (tier 3). You'll need a GP referral. However, NHS access varies significantly by region and waiting lists can be several months. Private access through online prescribers is generally faster, though you'll pay out of pocket.
How much weight loss can I expect in stone?
Average weight loss in clinical trials ranged from 15–21% of body weight for Mounjaro and around 15% for Wegovy. If you weigh 100kg (15st 10lbs), that could be roughly 15–21kg (2st 5lbs to 3st 4lbs) on average. However, individual results vary widely based on dose, adherence, diet, and activity level. Use our GLP-1 weight loss calculator for a personalised estimate.
Do I need to change my diet and exercise while taking these medications?
Yes. Clinical trials showed weight loss happened alongside reduced-calorie diet and increased physical activity. The medication supports appetite control, but sustainable weight loss requires lifestyle changes. A prescriber will discuss realistic expectations and healthy behaviour changes as part of treatment.
How do I know if I'm eligible for prescription weight loss medication?
You're typically eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your BMI instantly. Then speak with your GP, who can assess your overall health and whether prescription medication is suitable for you based on your individual circumstances.
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.