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 Per Month in the UK?
Each Mounjaro KwikPen contains exactly 4 weekly doses, which means you need one pen per month. The number of pens you'll need depends on your dose and treatment duration. In the UK, Mounjaro is available through NHS specialist services or private prescription following a clinical assessment. Understanding your monthly pen requirement and cost helps you plan treatment sustainably alongside lifestyle changes like diet and 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 Pens and Monthly Dosing in the UK
Each Mounjaro KwikPen contains 4 weekly doses, so you require one pen per month during treatment. Here's how the dosing structure works: Mounjaro uses a step-up approach where you start at 2.5mg weekly and increase every 4 weeks to find your effective maintenance dose (5mg, 7.5mg, 10mg, 12.5mg, or 15mg maximum). This means your initial treatment month uses one 2.5mg pen, then one pen at your next dose level, and so on. Because each pen lasts exactly 4 weeks, your monthly supply is predictable and consistent. UK pricing varies depending on whether you access Mounjaro through the NHS or via private prescription. On the NHS, there is no monthly cost to the patient — prescriptions are dispensed through tier 3 specialist weight management services. Privately, monthly costs range from approximately £150–£320 depending on your dose and the prescribing service you use. Your GP or prescriber will discuss the appropriate starting dose and escalation schedule for your individual health profile.
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.
NHS vs Private Access to Mounjaro in the UK
NHS access requires referral to a tier 3 specialist weight management service through your GP. Availability varies significantly across regions (integrated care boards), and waiting lists can extend several months to over a year in many areas. Once approved and on treatment, Mounjaro is dispensed at no cost via NHS prescription. Private prescription access is faster — available through online consultations with UK-licensed prescribers affiliated with GPhC-registered pharmacies. A private clinical assessment typically takes 1–2 days, and treatment can begin within days if approved. You pay per dose or monthly depending on the service provider. Private access suits those needing faster treatment or those whose NHS waiting list is very long. Both routes require clinical eligibility assessment and are not suitable for everyone.
- 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 often do I need to reorder Mounjaro pens?
You need one Mounjaro KwikPen per month (every 4 weeks). Each pen contains 4 weekly injections. If you're increasing your dose every 4 weeks during the titration phase, you'll receive a new pen with the higher dose each month. Once you reach your maintenance dose, you'll continue with one pen monthly at that same strength.
Is Mounjaro cheaper on the NHS or private prescription in the UK?
On the NHS, Mounjaro is free to patients (standard prescription cost applies in England — currently £9.90 per item). Privately, costs range from approximately £150–£320 per month depending on your dose and the prescribing service. NHS access requires a waiting list referral; private access is faster but costs money upfront.
Can I switch between Mounjaro doses mid-month?
No. Mounjaro pens are dose-specific — each pen contains one fixed strength. You cannot split a pen or adjust the dose mid-week. Dose changes happen every 4 weeks (every new pen). Your prescriber will ensure you receive the correct dose pen for each month based on your titration schedule.
What happens if I miss a Mounjaro dose or injection?
If you miss your weekly injection, inject within 4 days of the scheduled date and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on the usual day. Never give yourself two injections to catch up. Always maintain at least 3 days between doses.
How do I store multiple Mounjaro pens at home?
Keep unopened pens in the refrigerator at 2–8°C in their original carton. They stay good until the expiry date. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. After 30 days of use, dispose of the pen even if it contains medication left.
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.