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 Long Does Mounjaro Last in the UK?
Mounjaro (tirzepatide) is administered as a once-weekly injection, with each KwikPen lasting exactly 4 weeks as it contains 4 pre-filled doses. However, the duration of your treatment—how long you take Mounjaro overall—depends on your individual response, weight loss goals, and whether you access it through the NHS or privately. Understanding both the pen supply duration and your overall treatment timeline helps you plan your weight management journey 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 KwikPen Duration and Cost in the UK
Each Mounjaro KwikPen contains 4 pre-filled doses, providing exactly one month (4 weeks) of treatment at the standard once-weekly injection schedule. You will need to order a new pen every 4 weeks to continue your treatment without interruption.
Private prescription costs in the UK typically range from £129 to £320 per month, depending on your dose level. Higher doses (15 mg) cost more than lower doses (2.5 mg). Most private online prescribers offer transparent pricing upfront, and many provide subscription options that may offer modest savings when ordering multiple months in advance. Costs do not include GP consultation fees, though many online prescribers bundle their clinical assessment into the medication price.
- 2.5–5 mg doses: approximately £129–£180/month privately
- 7.5–10 mg doses: approximately £180–£240/month privately
- 12.5–15 mg doses: approximately £240–£320/month privately
NHS access, where available through specialist tier 3 weight management services, is free at the point of use, though regional availability and waiting lists vary significantly across the UK.
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: Treatment Duration and Timelines
NHS Mounjaro access is available through specialist weight management services in some regions, but waiting lists can extend from several months to over a year depending on your ICB (Integrated Care Board) area. Once approved, treatment is free, but availability is postcode-dependent and requires GP referral into tier 3 services.
Private prescription access is typically faster—you can complete an online clinical assessment with a UK-licensed prescriber within 24–48 hours and receive your first prescription within days. Most people continue Mounjaro for 6–12 months or longer, though your prescriber will review whether to continue based on your progress, side effects, and health goals. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and track your progress monthly with our progress tracker tool to monitor real results alongside 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.
How long will one Mounjaro KwikPen last?
Each KwikPen contains 4 pre-filled doses, lasting exactly 4 weeks (one month) when using the standard once-weekly injection schedule. You'll need to order a new pen every 4 weeks to maintain continuous treatment without gaps.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£320 per month depending on your dose. Lower starting doses (2.5–5 mg) cost around £129–£180, while higher maintenance doses (12.5–15 mg) cost £240–£320. Many providers offer subscription discounts for advance orders.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro is approved by NICE for NHS use through specialist tier 3 weight management services. However, availability is limited by region, and waiting lists can be very long (months to over a year). You'll need a GP referral to access NHS tirzepatide treatment.
How long will I need to take Mounjaro?
Treatment duration varies by individual. Most people continue for 6–12 months or longer, depending on weight loss progress, side effects, and your health goals. Your prescriber will review your treatment regularly and decide whether to continue, pause, or stop based on your response.
What's the difference between NHS and private Mounjaro access?
NHS Mounjaro is free but involves referral, waiting lists, and regional availability issues. Private access is faster (24–48 hours) and doesn't require NHS referral, but costs £129–£320/month. Both require a clinical assessment from a licensed prescriber before treatment starts.
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.