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 Ml In Mounjaro Pen — Dosing Explained
Mounjaro comes in a pre-filled KwikPen device, and the dosing is measured in milligrams (mg), not millilitres (ml). Each Mounjaro KwikPen contains a 4-week supply with four separate doses already pre-filled and ready to inject. The pen uses a simple dial mechanism to select your prescribed dose. Understanding how your Mounjaro pen works is essential for safe, consistent weight management alongside a reduced-calorie diet and increased physical activity.
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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 KwikPen Dose Amounts And Supply
Mounjaro is supplied as a pre-filled KwikPen that contains exactly 4 weeks of doses — one injection per week. Each pen delivers your prescribed dose automatically via a dial system. The doses available are: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. Each individual dose is already measured within the pen; you do not measure millilitres yourself. When you dial your dose number on the KwikPen, the device automatically dispenses the correct amount. After 4 weeks of use, you discard the empty pen and receive a new one with your next prescription. Your prescriber will determine which dose is right for you during your initial clinical assessment and may adjust it over time as part of dose titration. The pen should be stored in a refrigerator at 2–8°C before first use, and can be kept at room temperature below 30°C for up to 30 days after opening.
Clinically BackedWeight Loss
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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.
Mounjaro Injection Versus Oral Medications
Unlike oral weight loss medications, Mounjaro is an injectable tirzepatide — a dual GIP and GLP-1 receptor agonist. Because it is injected, the dose is measured in milligrams of active drug rather than liquid volume. This is different from some other injectable GLP-1 medications like Saxenda (liraglutide), which is dosed in mg but injected daily. Mounjaro's once-weekly dosing via KwikPen makes it convenient for consistent use. Each weekly injection may help reduce appetite and support feeling fuller after meals, alongside lifestyle changes. Your GP or prescriber will explain how to use the KwikPen correctly and answer any questions about your specific dose or UK eligibility for tirzepatide treatment.
- 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 KwikPen contain the same amount of liquid?
Each KwikPen contains the same total volume of solution, but the device is pre-calibrated so that when you dial your prescribed dose (e.g. 5 mg, 10 mg, or 15 mg), it delivers only that amount. You do not measure or adjust liquid yourself — the pen does it automatically.
How is Mounjaro different from Wegovy in terms of dosing?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both once-weekly injections but use different mechanisms. Mounjaro is a dual GIP/GLP-1 agonist with doses up to 15 mg, whilst Wegovy is a GLP-1-only agonist with doses up to 2.4 mg. Both require a UK prescription and clinical assessment.
Can I refill my Mounjaro KwikPen or do I get a new one each month?
You receive a new pre-filled KwikPen every 4 weeks. After using all four doses, you discard the empty pen. You do not refill it. Your prescriber will issue a new prescription for the next month's supply.
What should I do if I accidentally dial the wrong dose on my Mounjaro pen?
If you dial incorrectly before injecting, you can dial back to zero and start again. If you have already injected, contact your prescriber or pharmacist for guidance. Never try to inject a second dose to "make up" for a missed or incorrect dose.
Is Mounjaro available on the NHS in the UK, and how do I check eligibility?
Mounjaro is NICE-approved and available through NHS specialist tier 3/4 weight management services, though availability and waiting times vary by region. You can also access it privately via a UK-licensed prescriber following an online clinical assessment. Your GP can advise on both routes.
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.