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 Calculation With Prescription Medication in the UK
Working out your potential weight loss depends on your starting point, health goals, and available treatment options. If you're looking to understand how much weight you might lose with prescription medication in the UK, this guide covers eligibility, the three main licensed options, and how to access them through the NHS or privately. Even modest weight loss of 5–10% of your body weight can significantly improve health markers like blood pressure and blood sugar control.
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 Prescription Weight Loss Options
Three medications are currently licensed in the UK for weight management in eligible adults: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, while Saxenda is a daily injection.
In clinical trials, average weight loss varied by medication and dose. Mounjaro users lost approximately 15–21% of their body weight, while Wegovy users lost around 15% on average — though individual results differ significantly. These medications work best alongside a reduced-calorie diet and increased physical activity, not as standalone treatments.
Eligible adults typically have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage. Use our free BMI calculator above to check where you currently stand.
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 Next Steps
NHS access: Weight loss medications are available through specialist tier 3 or tier 4 weight management services, but you'll need a GP referral. Waiting times vary significantly by region — some areas have substantial waiting lists. Ask your GP about local specialist weight management services.
Private access: UK-licensed prescribers assess eligibility via online consultation, and medications are dispensed by registered pharmacies without an NHS referral. This route is typically faster but involves upfront costs.
Your first step is speaking with your GP about weight management options and whether prescription medication might be suitable for you. They can discuss your individual circumstances, health conditions, and goals. Alternatively, you can explore private options by consulting a UK-licensed prescriber. Track your progress over time using our free progress tracker.
- 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 do I calculate if I'm eligible for weight loss medication in the UK?
Check your BMI using our free BMI calculator on this page. You're typically eligible if your BMI is 30 or above, or 27–29.9 with weight-related conditions like diabetes or high blood pressure. Lower thresholds apply for certain ethnic backgrounds. Your GP or a licensed prescriber will do a full health assessment before prescribing.
How much weight can I expect to lose with prescription medication?
Clinical trials show average weight loss of 15–21% of body weight depending on the medication and dose — but individual results vary considerably. Some people lose more, some less. Weight loss works best alongside dietary changes and increased activity, not as a standalone treatment.
Can I access weight loss medication through the NHS?
Yes, through specialist weight management services (tier 3 or 4). You'll need a GP referral, but availability and waiting times vary significantly by region. Private access is also available via UK-licensed prescribers without an NHS referral, though this involves costs.
What's the difference between Mounjaro, Wegovy, and Saxenda?
All three are prescription-only UK-licensed medications, but they work differently. Mounjaro is a dual GIP/GLP-1 agonist (once-weekly), Wegovy is a GLP-1 agonist (once-weekly), and Saxenda is a GLP-1 agonist (daily injection). Your prescriber will recommend the best option based on your health profile.
What should I do if I think I'm eligible for weight loss medication?
Start by talking to your GP about weight management options, your health goals, and whether prescription medication might suit you. They can refer you to specialist services or discuss private options. A licensed prescriber will assess your individual circumstances before any medication is prescribed.
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.