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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What Does 5 x 18 Mean in Wegovy Dosing?
In Wegovy weight loss injections, "5 x 18" refers to the standard UK dosing schedule where patients receive 5 weekly injections at a specific dose, with the notation sometimes used to describe dose escalation phases. Wegovy (semaglutide) is a prescription-only GLP-1 receptor agonist licensed in the UK for weight management in adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Understanding how this notation works helps clarify what to expect during treatment. This UK health guide explains Wegovy dosing conventions and what they mean for your weight management journey.
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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.
How Wegovy Dosing Works in the UK
Wegovy dosing follows a gradual escalation schedule over approximately 16–20 weeks, starting at a low dose and increasing every 4 weeks to minimise side effects and allow your body to adjust. The standard dose progression is:
- 0.25 mg — weeks 1–4 (starting dose)
- 0.5 mg — weeks 5–8
- 1 mg — weeks 9–12
- 1.7 mg — weeks 13–16
- 2.4 mg — week 17 onwards (maintenance dose)
Each dose is injected once weekly. The "5 x 18" notation sometimes appears in clinical literature to indicate 5 weeks at a particular dose level, though UK prescribers typically refer to the actual mg dose rather than this notation. In clinical trials (STEP-1), patients on the 2.4 mg maintenance dose lost an average of approximately 14.9% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Use our free BMI calculator above to check your current BMI and see whether you might be eligible for prescription weight loss treatment.
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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.
Wegovy vs Ozempic — Why the Distinction Matters
A common source of confusion: both Wegovy and Ozempic contain semaglutide, but they are not interchangeable for weight loss. Ozempic is approved for type 2 diabetes management (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is specifically licensed for weight management at higher doses (up to 2.4 mg). Using Ozempic off-label for weight loss is not recommended practice in the NHS. If you're considering weight loss medication, ask your GP or prescriber whether Wegovy is appropriate for you. Access in the UK is through NHS specialist tier 3 services (with potential waiting lists) or private online prescribing following a clinical assessment. Our GLP-1 weight loss calculator can help you explore projected outcomes at different doses.
- 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 "5 x 18" notation mean on Wegovy prescriptions?
"5 x 18" isn't standard UK prescription notation for Wegovy. Prescribers typically refer to the actual dose in mg (0.25 mg to 2.4 mg). This notation may appear in older clinical trial literature indicating 5 weeks at a particular dose. If you see unfamiliar notation on your prescription, ask your prescriber or pharmacist to clarify.
How long does it take to reach the full 2.4 mg dose of Wegovy?
The standard escalation takes approximately 16–20 weeks. You start at 0.25 mg and increase every 4 weeks: 0.25 → 0.5 → 1 → 1.7 → 2.4 mg. You must spend at least 4 weeks on each dose before increasing. Some patients stay longer on lower doses if side effects occur.
Is Wegovy available on the NHS in the UK?
Wegovy is available through NHS specialist weight management services (tier 3), but access varies significantly by region and waiting times can be long. It's also available privately through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber.
What weight loss should I expect with Wegovy?
Clinical trials showed an average weight loss of approximately 14.9% of body weight over 68 weeks on the 2.4 mg dose, alongside dietary changes and increased activity. Results vary considerably between individuals. Some people lose more, others less. Weight loss depends on adherence, lifestyle factors, and individual metabolism.
Can I switch from Ozempic to Wegovy for weight loss?
Any switch between medications must be managed by your prescriber — never change medications independently. Ozempic is not licensed for weight loss in the UK, so a prescriber would need to reassess your situation and issue a new Wegovy prescription if appropriate. This is a clinical decision based on your individual health.
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.