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 Clicks On A Mounjaro Pen?
A Mounjaro KwikPen doesn't work with traditional "clicks" — instead, each pre-filled pen delivers one complete weekly dose automatically. The pen shows a colour-coded dose window and simply clicks once when you press the injection button, administering the full 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg dose in a single injection. Understanding how the Mounjaro pen works and how tirzepatide dosing progresses is important before starting treatment through NHS or private prescription routes in the UK.
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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.
How The Mounjaro KwikPen Delivery System Works
The Mounjaro KwikPen is a pre-filled, single-use injection device manufactured by Eli Lilly. Unlike insulin pens with adjustable dose dials, each Mounjaro pen contains one fixed dose and cannot be adjusted. When you press the injection button, the mechanism automatically delivers the entire dose in a single click-like motion. The pen features a colour-coded dose window on the side that displays your current dose strength (yellow for 2.5 mg, blue for 5 mg, purple for 7.5 mg, grey for 10 mg, green for 12.5 mg, and red for 15 mg). Each KwikPen pen is supplied as a four-pack, providing four weeks of once-weekly injections at the same dose level. The needle is fine (31-gauge), and the entire injection typically takes a few seconds. You rotate injection sites weekly between your stomach (most common), upper thigh, or upper arm. After injection, the needle retracts automatically for safety.
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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 And Accessing Treatment In The UK
Mounjaro dosing follows a structured titration schedule, meaning your dose increases gradually over weeks. You start at 2.5 mg for weeks 1–4, then step up to 5 mg for weeks 5–8, and continue escalating every 4 weeks (7.5 mg, 10 mg, 12.5 mg) until reaching the maximum 15 mg maintenance dose. This gradual increase helps your body adjust and typically reduces side effects. In the UK, you can access Mounjaro through NHS specialist tier 3 weight management services (eligibility varies by region) or via private prescription following an online consultation with a UK-licensed prescriber. Private costs range from approximately £129–£280 per month depending on your dose, though prices vary between GPhC-registered pharmacies. Your prescriber will assess your BMI (typically 30 or above, or 27+ with weight-related conditions) and discuss whether tirzepatide is suitable before issuing a prescription.
- 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 KwikPen is empty?
Each KwikPen contains exactly one weekly dose. Once you've injected, the pen is empty and must be disposed of. You'll receive a fresh pen the following week. The colour-coded window helps you identify your dose strength before injection — if the window shows your expected colour, the pen is ready to use.
Can I reuse a Mounjaro pen?
No. Each Mounjaro KwikPen is single-use only and cannot be refilled. After your weekly injection, dispose of the pen safely in a sharps bin (your pharmacy or GP surgery can provide one). A new pen is supplied weekly as part of your prescription.
What's the difference between Mounjaro and Wegovy pens?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both once-weekly injectable pens but deliver different medications at different dose ranges. Mounjaro uses a KwikPen device and doses up to 15 mg, while Wegovy uses an auto-injection pen with maximum dose 2.4 mg. Mounjaro is a dual GIP and GLP-1 agonist, whereas Wegovy is a GLP-1 agonist only. Both are prescription-only in the UK.
How do I access Mounjaro on the NHS in the UK?
NHS access to Mounjaro (tirzepatide) is through specialist tier 3 weight management services, typically requiring a GP referral. Availability varies significantly by region, and waiting lists can be lengthy. Your GP can advise whether your local integrated care board offers tirzepatide through NHS services. Private prescription is faster — available through online consultations with licensed UK prescribers.
What happens if I miss a Mounjaro dose?
If you miss your weekly dose, inject as soon as you remember if it's within 4 days of the scheduled date. If more than 4 days have passed, skip that dose and inject on your normally scheduled day the following week. Never take two doses close together. Your prescriber or pharmacist can provide specific guidance for your situation.
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.