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
When To Order Your Next Mounjaro Pen
Mounjaro comes in a pre-filled KwikPen device containing four weekly doses, so you'll need to reorder every 28 days. In the UK, you can access tirzepatide through NHS specialist weight management services or private prescription following an online clinical assessment. Understanding when to reorder, what it costs, and how the UK access routes work will help you stay on track with your treatment without disruption.
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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.
Mounjaro Ordering Timeline & Supply Management
Each Mounjaro KwikPen contains exactly four weekly injections, meaning a single pen lasts approximately 28 days. You should plan to order your next pen around day 24–26 to ensure it arrives before your current supply runs out. If you're receiving treatment through an NHS specialist service, your prescriber will advise on their ordering schedule and how prescriptions are managed. For private prescription access, you'll place an order through your chosen provider, submit a clinical questionnaire if you're a new patient or haven't been assessed recently, and receive your next pen within 2–5 working days depending on stock availability.
- Each KwikPen = 4 weekly doses (28-day supply)
- Reorder timing: days 24–26 of your current pen
- Unopened pens store in the fridge at 2–8°C
- Never freeze — frozen pens cannot be used
- After first use, pens can be kept at room temperature (below 30°C) for up to 30 days
Tracking your injection schedule using a simple calendar or our free progress tracker can help you remember when to reorder and stay consistent with your weekly doses.
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.
Mounjaro Cost & Private Prescription Access in the UK
Mounjaro is not currently available through standard NHS GP prescription — access is through specialist tier 3 weight management services following a formal referral. However, NHS availability is extremely limited and waiting lists can stretch to many months in some areas. Private prescription access is available immediately without an NHS referral. Cost varies by provider and dose, typically ranging from approximately £129–£320 per month depending on whether you're on a starting dose (2.5 mg) or maintenance dose (5–15 mg). You'll need a UK-licensed prescriber to assess your eligibility based on your BMI, health conditions, and medical history before issuing a prescription to a GPhC-registered pharmacy.
- NHS route: referral to specialist weight management service (long waiting lists)
- Private route: online clinical assessment with UK-licensed prescriber (immediate access)
- Both routes require a prescription — neither is available to purchase without clinical assessment
- 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 when my Mounjaro pen is running out?
Each KwikPen delivers four weekly injections over 28 days. Mark your calendar for your fourth injection and plan to reorder around days 24–26. Most patients receive reminder notifications from their prescription provider, but setting a phone alarm is also helpful to avoid gaps in treatment.
Can I store multiple Mounjaro pens at home?
Yes, unopened pens store safely in the fridge at 2–8°C for many months until the expiry date. Keep them in their original carton away from light. Once opened, use the pen within 30 days even if doses remain. Never freeze pens as this damages the medication.
What's the difference between NHS and private Mounjaro access in the UK?
NHS access is through specialist weight management services (with long waiting lists and regional variation). Private prescription access is available immediately following an online clinical assessment with a UK-licensed prescriber and costs £129–£320 per month depending on dose. Both require a valid prescription.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£320 per month depending on your dose and the provider. Starting doses cost less than maintenance doses. Some providers offer subscription discounts if you commit to regular monthly orders, but individual costs vary — check directly with providers for current pricing.
What happens if I can't order my next Mounjaro pen in time?
Contact your prescription provider as soon as possible if you anticipate a gap. Many can arrange expedited delivery or may provide temporary emergency supply. Gaps in treatment should be avoided as stopping and restarting can affect tolerance. Your prescriber can advise on managing any delays. ```
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.