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
When Should I Take Mounjaro?
Mounjaro (tirzepatide) is a once-weekly injection prescribed in the UK for weight management. The timing of your Mounjaro injection is flexible — you choose the day that suits your routine best. Once you pick your injection day, aim to take it on the same day each week, ideally at a similar time. This consistency helps maintain steady hormone levels and supports the medication's effectiveness. Always follow your prescriber's specific guidance, as individual dosing schedules may vary based on your health needs.
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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 Injection Scheduling and Consistency
Mounjaro is administered once every 7 days — you have complete flexibility in choosing which day of the week suits you best. Many people choose a day that's easy to remember, such as a Monday morning or Friday evening. The key is consistency: once you select your injection day, stick to it each week to maintain stable tirzepatide levels in your bloodstream.
- Pick a day and time that fits naturally into your routine
- Set a phone reminder if helpful to avoid missed doses
- Each KwikPen contains 4 weekly doses — plan ahead for pen storage
- Minimum 72 hours (3 days) must pass between consecutive injections
- If you miss a dose, inject within 4 days and resume your normal schedule
- Do not take two doses within 3 days to make up for a missed injection
The Mounjaro KwikPen is a pre-filled injection device with a clear dose counter. You can inject into your stomach (abdomen), upper thigh, or upper arm — rotate injection sites each week to minimise irritation.
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.
Storage and Preparing Your Mounjaro Dose
Proper storage ensures Mounjaro remains effective. Unopened pens must be kept in a refrigerator between 2°C and 8°C — do not freeze. Once you start using a pen, it can be stored at room temperature (below 30°C) for up to 30 days. After 30 days from first use, dispose of the pen safely.
Before injecting, remove the pen from the fridge 15–30 minutes before use — allowing it to reach room temperature makes injection more comfortable. Always check that the liquid is clear and colourless. If it appears cloudy or discoloured, do not use it. Your prescriber or pharmacist will provide full injection training when you receive your first 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.
Does the time of day matter when taking Mounjaro?
No specific time of day is required — you can inject Mounjaro morning, afternoon, or evening. The most important factor is consistency: choose the same day and time each week to maintain steady hormone levels. Pick whatever time fits naturally into your routine.
What if I forget my Mounjaro injection?
If you remember within 4 days of your scheduled dose, inject as soon as possible and resume your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on your normally scheduled day. Never inject two doses within 3 days.
Can I change my Mounjaro injection day?
Yes, you can change your injection day if needed. Simply pick a new day and begin injecting on that day from then onwards, maintaining at least 3 days (72 hours) between doses. Inform your prescriber of any significant changes to your dosing schedule.
Should I refrigerate Mounjaro between injections?
Once you've started using a Mounjaro pen, you can store it at room temperature (below 30°C) for up to 30 days. Unopened pens must stay refrigerated at 2–8°C. Check your pen's expiry date and discard 30 days after first use.
Does Mounjaro need to be injected at the same time as meals?
No, Mounjaro can be injected regardless of meal timing. You can inject before, during, or after eating. Consistency in your weekly injection day matters more than meal timing. Our BMI calculator can help you monitor progress alongside your prescribed treatment.
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.