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 Mounjaro Pens Do You Need Per Month?
Each Mounjaro KwikPen contains exactly 4 weekly doses, which means you'll use one pen every month if you're on a stable maintenance dose. However, the number of pens you receive depends on your current dose and whether you're still in the titration phase, where your dose increases every 4 weeks. Understanding your Mounjaro prescription helps you plan refills and track your treatment progress effectively.
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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 Pen Supply and Dose Titration Schedule
Mounjaro (tirzepatide) comes as a pre-filled KwikPen device, with each pen containing 4 once-weekly injections. This means one Mounjaro pen covers exactly 4 weeks of treatment. During the dose titration phase — where your prescriber gradually increases your dose — you'll typically receive pens matching your current dose level every 4 weeks.
The standard titration schedule works as follows:
- Weeks 1–4: 2.5 mg dose (1 pen)
- Weeks 5–8: 5 mg dose (1 pen)
- Weeks 9–12: 7.5 mg dose (1 pen)
- Weeks 13–16: 10 mg dose (1 pen)
- Weeks 17–20: 12.5 mg dose (1 pen)
- Week 21+: 15 mg maintenance dose (1 pen per month)
Once you reach your maintenance dose — typically the dose your prescriber considers optimal for you — you'll receive one pen per calendar month. If your prescriber decides to keep you on a lower maintenance dose (e.g. 5 mg or 10 mg), you'll still receive one pen per month at that dose.
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.
Planning Your Mounjaro Supply and Private Prescription Access
If you're accessing Mounjaro through NHS specialist weight management services, your prescriber will manage supply directly. If you're using a private online prescriber in the UK, you'll typically place orders for monthly supplies. Most private providers deliver pens on a subscription basis, allowing you to adjust or pause your order as needed.
Each KwikPen is supplied with 4 pre-filled needles and comes in a carton with storage instructions. Unopened pens must be refrigerated at 2–8°C; once opened, a pen can be kept at room temperature (below 30°C) for up to 30 days. Plan your refills carefully to ensure you don't run short, especially if you're between dose increases where you may need to time your next order around your prescriber's guidance.
- 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 one Mounjaro pen really last exactly a month?
Yes. Each KwikPen contains 4 weekly doses, so one pen covers exactly 4 weeks. Once you're on a stable maintenance dose, you'll use one pen per calendar month. During dose titration, you'll receive one pen every 4 weeks at your current dose level.
What if I'm increasing my dose — do I get multiple pens at once?
No. Your prescriber will typically issue a prescription for the appropriate dose every 4 weeks. You'll receive one pen containing your current dose, then return for assessment before moving to the next dose level. This ensures your prescriber can monitor your response.
How should I store my Mounjaro pens?
Unopened pens must be stored in a refrigerator at 2–8°C in their original carton. Once you've started using a pen (first injection taken), you can store it at room temperature below 30°C for up to 30 days. Never freeze pens — if frozen, they cannot be used. Dispose of the pen 30 days after first use.
Can I get Mounjaro on the NHS, and how does supply work?
NHS access is through specialist tier 3 weight management services — not standard GP prescription. Availability varies significantly by region. If approved by your NHS service, they'll manage your supply and dose titration directly. Waiting times can be lengthy in many areas.
What's the difference between Mounjaro and Wegovy pens in terms of monthly supply?
Both Mounjaro and Wegovy are once-weekly injections, so both use one pen per month on maintenance doses. However, Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with different dose escalation than Wegovy (semaglutide), a single GLP-1 agonist. Your prescriber will recommend whichever is appropriate for you.
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.