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 Often Is Mounjaro Injection in the UK?
Mounjaro (tirzepatide) is a once-weekly weight loss injection licensed in the UK for adults with obesity or overweight with health complications. You inject yourself once every seven days, typically on the same day each week. The dose starts at 2.5 mg and increases gradually over several weeks as your body adjusts. Understanding the injection frequency and dose escalation schedule is important for managing your treatment effectively. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses alongside your prescription plan.
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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 Dosing Schedule and Injection Frequency
Mounjaro is administered once weekly — this means you inject 2.4 ml (containing your prescribed dose) under the skin every seven days, ideally on the same day each week. Each pre-filled KwikPen device contains four doses (a four-week supply). The dosing schedule follows a titration protocol where you remain on each dose for a minimum of four weeks before escalating:
- Weeks 1–4: 2.5 mg (starting/adjustment dose)
- Weeks 5–8: 5 mg (first maintenance)
- Weeks 9–12: 7.5 mg (escalation if needed)
- Weeks 13–16: 10 mg (escalation if needed)
- Weeks 17–20: 12.5 mg (escalation if needed)
- Weeks 21+: 15 mg (maximum dose)
You do not skip weeks or double up doses. Missing a dose means injecting as soon as you remember if within four days — otherwise waiting for your next scheduled injection. Your prescriber will guide dose increases based on your tolerability and response, and you may stay on any dose longer than four weeks if it suits your needs.
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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.
Accessing Mounjaro in the UK: NHS vs Private Routes
NHS route: Mounjaro is available through NICE-approved tier 3 specialist weight management services following GP referral. Availability varies by region (Integrated Care Board), and waiting lists can extend several months or longer. NHS prescription comes at no additional cost if eligible, though access criteria are strict.
Private route: You can access Mounjaro privately through a UK-licensed prescriber via online consultation without NHS referral. A GPhC-registered pharmacy then dispenses your prescription. Private costs range from approximately £129–£320 per month depending on dose and provider. The prescription process typically takes 2–5 working days once approved. Both routes require clinical assessment of your BMI, health history, and eligibility before the first injection.
- 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.
Can I skip a Mounjaro injection week if I'm not ready?
No — consistency matters. Mounjaro works best with regular once-weekly injections. If you need to delay, contact your prescriber. Missing a dose and injecting more than four days late? Wait for your next scheduled injection day. Never take double doses to catch up. Skipping weeks can affect weight loss results.
How long does a Mounjaro KwikPen last?
Each pre-filled KwikPen contains four weeks of doses (one week per injection). You'll need a new pen every four weeks. Your prescriber or pharmacy will provide a new pen as part of your ongoing prescription. Storage is crucial — unopened pens must be refrigerated at 2–8°C.
What if I want to stop Mounjaro after starting?
You can stop at any time, but discuss it with your prescriber first. Stopping abruptly won't cause harm, but weight regain may follow. Some people continue on maintenance doses long-term; others pause and restart. Your prescriber can advise what suits your health goals and discuss any concerns.
Does Mounjaro work differently if I inject on different days each week?
Consistency is ideal — injecting on the same day weekly helps your body maintain steady hormone levels. If you occasionally inject a day or two early or late, it's unlikely to cause problems. But stick to a regular schedule for best results and to avoid missing doses accidentally.
How do I know if Mounjaro is working if I only inject once a week?
Weight loss typically appears after 4–8 weeks on a dose, though some people see changes sooner. Use our free BMI calculator and progress tracker to monitor your weight, measurements, and BMI weekly. Your prescriber will also review your progress at regular check-ins and adjust your dose if needed.
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.