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 A Mounjaro Pen?
A Mounjaro KwikPen is a pre-filled injection device that contains enough medication for 4 weekly doses, not a single large volume. Rather than measuring Mounjaro by total millilitres, each dose is measured in milligrams (mg), which is the standard way prescribers manage your treatment. Understanding how the pen works and how doses progress is important for anyone starting this prescription-only weight management injection.
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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.
Understanding Mounjaro KwikPen Dose Structure
Each Mounjaro KwikPen contains 4 pre-filled doses — one dose per week for 4 weeks. The medication is measured in milligrams (mg), not millilitres, because the concentration varies between different dose strengths. Available doses progress from 2.5 mg (starting dose) up to 15 mg (maximum dose). Your prescriber will determine which dose strength you need, and you'll receive a pen containing four weekly injections at that specific dose. For example, a 5 mg pen delivers four 5 mg injections. Each injection is administered once weekly, and after 4 weeks you'll need a new pen. The exact volume of liquid in each pen varies slightly depending on the dose, but this is automatically calibrated in the KwikPen design — you don't need to measure it yourself. When you inject, the pen automatically delivers the correct dose with each click-and-hold action.
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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 Dose Titration Schedule
Mounjaro dosing follows a careful titration schedule where your dose increases every 4 weeks if tolerated. You start at 2.5 mg weekly for 4 weeks, then increase to 5 mg, then 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg — each step lasting at least 4 weeks. This gradual escalation allows your body to adjust and helps minimise side effects like nausea. Your prescriber will assess your response at each stage before progressing. If you experience side effects, your prescriber may keep you at your current dose longer or adjust the schedule. Most people find their optimal dose somewhere between 5 mg and 15 mg, and many remain on doses lower than the maximum. Always follow your prescriber's guidance — never adjust doses independently. Use our GLP-1 weight loss calculator to see how different dose levels are associated with different weight loss outcomes in clinical trials.
- 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.
Is Mounjaro measured in ML or MG?
Mounjaro is measured in milligrams (mg), not millilitres (ml). This is the standard for prescription medications — the dose strength indicates the amount of tirzepatide in each injection. The actual volume of liquid varies by dose but is automatically calibrated in the KwikPen device.
How long does one Mounjaro KwikPen last?
One pen lasts exactly 4 weeks — it contains 4 weekly injections. After 4 weeks, you'll need a new pen. If you're still at the same dose, you'll receive the same pen strength. If you're escalating doses as part of the titration schedule, your next pen will contain a higher dose.
Can I store a Mounjaro pen after opening it?
Yes. Unopened pens must stay refrigerated at 2–8°C in their original carton. Once you use the first dose from a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Dispose of the pen 30 days after first use, even if doses remain.
What's the difference between Mounjaro and Wegovy dosing?
Mounjaro (tirzepatide) and Wegovy (semaglutide) use different dose ranges because they're different medications. Mounjaro starts at 2.5 mg and goes up to 15 mg weekly; Wegovy starts at 0.25 mg and goes up to 2.4 mg weekly. Approximate clinical equivalence exists (e.g. Mounjaro 5 mg ≈ Wegovy 0.5 mg), but any switch must be managed by your prescriber.
Is Mounjaro available on the NHS in the UK?
Mounjaro has been approved by NICE for NHS use within specialist tier 3 weight management services. However, availability varies significantly by region and waiting lists can be substantial. Your GP can refer you to local services. Many people access Mounjaro privately through GPhC-registered online prescribers following a clinical assessment.
Ready to take control of your weight loss journey?
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