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
Exercise Is Not The Key To Weight Loss — Why Medication Matters
While exercise is important for overall health, research shows that diet is the primary driver of weight loss. Many UK adults struggle to lose weight through exercise alone — especially those living with obesity or weight-related health conditions. The good news is that prescription weight loss medications are now available on the NHS and privately for eligible adults. Understanding what actually works for weight management, and what options exist in the UK, can help you make informed decisions about your health.
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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 Options
Three GLP-1 and dual-action medications are licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist. In clinical trials, it helped participants lose an average of 15–21% of their body weight when combined with lifestyle changes. It's a once-weekly injection.
- Wegovy (semaglutide) — a GLP-1 receptor agonist. Clinical trials showed average weight loss of around 15% of body weight. Also a once-weekly injection.
- Saxenda (liraglutide) — another GLP-1 agonist, taken as a daily injection.
You're eligible if you 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 cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, lower BMI thresholds apply. Use our free BMI calculator above to check your current BMI and understand where you fall.
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.
How To Access Weight Loss Medication In The UK
NHS access is through specialist tier 3 weight management services — you'll typically need a referral from your GP. Availability and waiting times vary significantly by region. Private access is available through UK-licensed online prescribers following a consultation; you don't need an NHS referral. Either way, a qualified prescriber will assess whether prescription weight loss medication is suitable for you.
Your GP is the best starting point. Discuss your weight management goals, any weight-related health conditions, and ask about both NHS services and private options in your area. Even if you're not eligible for prescription medication yet, your GP can signpost you to evidence-based weight management programmes. You can also calculate your BMI and use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
Q1: Why isn't exercise alone enough for weight loss? A1: Weight loss depends on creating a calorie deficit, which is primarily achieved through diet. While exercise is vital for cardiovascular health, muscle strength, and mental wellbeing, it burns relatively fewer calories than most people think. Most weight loss comes from eating fewer calories — around 80% diet, 20% exercise is a common guideline. This is why prescription weight management options focus on appetite regulation and calorie reduction alongside lifestyle change. Q2: How does Mounjaro work differently from Wegovy? A2: Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways for appetite control. Wegovy is a GLP-1 receptor agonist only, activating one pathway. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs 15%), but individual results vary significantly. Both work best alongside a reduced-calorie diet and increased physical activity. Q3: Am I eligible for NHS weight loss medication? A3: 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 (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). For South Asian, Chinese, Black African, or Black Caribbean adults, thresholds are lower. Your GP can assess your individual eligibility and refer you to specialist services if appropriate. Q4: What's the difference between NHS and private weight loss medication? A4: NHS access is through specialist weight management services (tier 3) — free but subject to regional availability and waiting lists. Private access is through UK-licensed online prescribers — faster but comes with a cost (typically £130–£320 per month depending on dose). Both require a clinical assessment and prescription. Your GP can discuss both pathways with you. Q5: Can I use our weight loss calculator to estimate my potential results? A5: Yes — our free GLP-1 weight loss calculator lets you explore potential weight loss outcomes at different medication doses based on clinical trial data. Remember that individual results vary significantly, and weight loss depends on medication, diet, physical activity, and personal factors. Use it as a guide alongside a conversation with your GP or prescriber for personalised advice.- 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 is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
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.