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 You Inject Mounjaro — Morning or Night?
There is no specific requirement to inject Mounjaro in the morning or at night — you can take your weekly injection at any time that suits your schedule. The important thing is consistency: pick the same day and time each week and stick to it. Your prescriber or the information leaflet will advise on injection technique, storage, and what to do if you miss a dose. Always follow guidance from your healthcare professional or the KwikPen instructions.
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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 to Choose Your Mounjaro Injection Time
The timing of your Mounjaro injection depends entirely on your personal preference and routine. The active ingredient, tirzepatide, works consistently regardless of whether you inject in the morning or evening. What matters most is choosing a time you can remember and maintain week after week.
- Morning injection — suits people who prefer to get their weekly task done early
- Evening injection — works well if you prefer injecting before bed or after work
- Midweek timing — many people choose Wednesday or Thursday to space doses evenly
Once you select your injection day and time, mark it in your calendar or set a phone reminder. Consistency helps you remember your dose and allows your body to maintain steady medication levels. If you accidentally inject at a different time one week, simply return to your normal schedule the following week — do not take a double dose.
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 Preparation Tips for Your KwikPen
Storage affects when you can inject. Unopened Mounjaro pens must be stored in the refrigerator at 2–8°C. Once you start using a pen, it can be kept at room temperature (below 30°C) for up to 30 days. This flexibility means you can inject at home, at work, or when travelling — as long as your pen has been stored correctly.
Before injecting, allow the pen to reach room temperature for 15–30 minutes if it has been refrigerated. Never inject a frozen pen. Wash your hands, clean the injection site with an alcohol wipe, and follow the step-by-step instructions on your KwikPen. Rotate injection sites weekly between your stomach, thigh, and upper arm to reduce irritation.
- 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 injecting Mounjaro at night affect sleep or side effects?
No — tirzepatide works the same regardless of injection time. Some people find evening injections convenient before bed, while others prefer morning. If you experience nausea (a common side effect), timing your injection when you can rest or have lighter meals nearby may help manage it.
What if I forget my weekly Mounjaro injection?
If you remember within 4 days of your scheduled time, inject as soon as you remember, then continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on your normal scheduled day. Never take a double dose.
Can I change my Mounjaro injection time or day?
Yes — you can change your injection day or time if needed. Simply choose a new day that works better for you and stick to it consistently. Ensure at least 72 hours (3 days) between each injection. Inform your prescriber if you make a significant change.
Does Mounjaro need to be injected at the same time every week?
No — the medication will work effectively at different times. However, injecting on the same day each week makes it easier to remember your dose and maintains consistent medication levels in your body. A reminder on your phone can help.
Is there a best time to inject Mounjaro with food?
Mounjaro can be injected regardless of whether you have eaten. You do not need to avoid food before or after injection. If nausea is an issue, some people find it helpful to inject when they plan to have a light meal or snack nearby.
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.