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
How Many Doses of Mounjaro Come in Each Pen?
Each Mounjaro KwikPen contains exactly 4 weekly doses, providing one month's supply of treatment. This UK prescription injection comes pre-filled and ready to use. If you're considering tirzepatide (Mounjaro's active ingredient) as part of your weight management plan, understanding the pen format and dosing schedule helps you plan your treatment. Our GLP-1 weight loss calculator can help you explore what results might look like at different Mounjaro doses, while our BMI calculator shows where you currently sit on NHS guidelines.
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.
Mounjaro Pen Format vs Wegovy — Key Differences
Mounjaro KwikPen format: Each pen contains 4 pre-filled doses of 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg (depending on your dose strength). You inject once weekly for 4 weeks, then order a new pen.
Wegovy pen format: Each pre-filled auto-injection pen also contains 4 weekly doses, but semaglutide comes in different dose strengths (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, or 2.4 mg).
Key difference: Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1 agonist only. In the SURMOUNT clinical trials, Mounjaro at 15 mg showed average weight loss of approximately 21% body weight, whilst Wegovy at 2.4 mg (maximum dose) showed approximately 15% in STEP trials. Both are prescription-only and require clinical assessment before use.
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.
Which Medication Suits You — Clinical Assessment Matters
Neither Mounjaro nor Wegovy is suitable for everyone. Your prescriber will assess whether you meet NHS eligibility criteria: a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or high blood pressure. If you're of South Asian, Chinese, Black African, or Caribbean heritage, lower thresholds may apply due to higher health risks at lower BMI levels.
Both medications work best when combined with reduced-calorie diet and increased physical activity. Individual results vary significantly. A licensed UK prescriber will review your medical history, current medications, and health goals to decide which injection format and mechanism is appropriate for you. Try our GLP-1 weight loss calculator to estimate potential outcomes, and use our progress tracker to monitor your journey once treatment starts.
- 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.
Does each Mounjaro pen last a whole month?
Yes, each KwikPen contains 4 weekly doses, lasting exactly 4 weeks. After 4 weeks, you need a new pen. The pen remains in your fridge between doses and must be discarded 30 days after first use, even if some medication remains.
Can I switch between Mounjaro and Wegovy once I start treatment?
Switching between medications must only be done under prescriber guidance. Whilst approximate dose equivalences exist (Mounjaro 15 mg ≈ Wegovy 2.4 mg), there is no official conversion chart. Your prescriber will manage any switch carefully, considering your response and tolerance.
What happens if I lose or damage my Mounjaro pen?
Contact your prescriber or pharmacy immediately — they can arrange a replacement. Do not attempt to refill or repair the pen yourself. If you've missed a dose, contact your healthcare provider for guidance on timing your next injection.
Are Mounjaro pens available on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval, but access varies significantly by region and local health board. Waiting lists can be lengthy. Private prescribing via UK-licensed online providers offers faster access without NHS referral.
How do I store my Mounjaro pen between weekly injections?
Keep unopened pens in the fridge at 2–8°C. Once you start using a pen, it can be stored at room temperature (below 30°C) for up to 30 days. Never freeze. Keep in the original carton away from light and heat to protect the medication.
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.