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 Calculator and NHS Prescription Options
If you're looking for a weight loss calculator combined with NHS information, you'll want to understand your prescription options. The UK offers several licensed medications for weight management—Mounjaro, Wegovy, and Saxenda—available through NHS specialist services or private prescription. This guide covers eligibility, how these medications work, and the difference between NHS and private access. Use our free weight loss calculator above to explore potential outcomes, then speak with your GP about whether prescription support might be right for you.
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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 Loss Medications
Three GLP-1 receptor agonist medications are currently licensed in the UK for weight management in adults. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist offering once-weekly injections at doses up to 15 mg, with clinical trials showing average weight loss of 15–21% of body weight. Wegovy (semaglutide) is a GLP-1-only injection, also once-weekly, up to 2.4 mg, with trials showing approximately 15% average weight loss. Saxenda (liraglutide) is a daily injection option at up to 3 mg.
You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, hypertension, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to increased health risk at lower weights. Use our BMI calculator to check your current BMI and understand where you sit on the NHS weight management spectrum.
Important: All three medications are prescription-only and require clinical assessment before being prescribed. They work best alongside reduced-calorie diet and increased physical activity—they are not a standalone solution.
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
NHS access: Prescription weight loss medication is available through NHS tier 3 specialist weight management services. You'll need a referral from your GP, and availability varies significantly by region and ICB (Integrated Care Board). Waiting lists can be several months or longer in many areas. Once accepted into a specialist service, you'll be assessed for suitability and supported throughout treatment at no direct cost.
Private access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. No NHS referral needed, and treatment can begin much sooner. Costs typically range from £129–£320 per month depending on medication and dose. Speak with your GP first—they can advise whether prescription medication is appropriate for you and may be able to support your choice, even if prescribing privately.
- 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 know if I'm eligible for prescription weight loss medication?
You may be eligible if your BMI is 30 or above, or 27–29.9 with a weight-related condition like type 2 diabetes or high blood pressure. Lower thresholds apply for certain ethnic backgrounds. Use our free BMI calculator to check your BMI, then speak with your GP about eligibility. They can assess your individual health and discuss whether medication is appropriate for you.
Can I access weight loss injections like Mounjaro or Wegovy on the NHS?
Yes, Mounjaro and Wegovy are available through NHS specialist weight management services. However, access requires a GP referral to tier 3 services and varies by region. Waiting times can be lengthy. Alternatively, these medications are available through private prescription following an online clinical assessment. Your GP can advise on the best option for you.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with clinical trials showing 15–21% average weight loss, whilst Wegovy (semaglutide) is a GLP-1-only injection with approximately 15% average loss. Mounjaro uses once-weekly injections up to 15 mg; Wegovy up to 2.4 mg. Individual results vary. Your prescriber will advise which is more suitable for you.
Are weight loss injections safe?
UK-licensed weight loss medications have been through rigorous safety testing and are monitored by the MHRA. Common side effects include nausea and diarrhoea, which often improve over time. Serious side effects are rare. However, they're not suitable for everyone—pregnant women, those with a history of thyroid cancer, and others may not be able to use them. A prescriber will assess your suitability.
Do I need to change my diet and exercise while taking weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. They support appetite control and help you feel fuller, but they're not a replacement for lifestyle changes. Our GLP-1 weight loss calculator can help you estimate potential outcomes when combined with diet and exercise changes.
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.