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 Take Your Mounjaro Injection?
Mounjaro (tirzepatide) is a once-weekly prescription injection for weight management. The best time to take Mounjaro is flexible — you choose a day that suits your routine and stick to it consistently. Unlike some medications that require specific timing with meals, Mounjaro can be injected on any day of the week, at any time of day, with or without food. The key is consistency: pick the same day each week and inject around the same time. This helps you build a routine and reduces the chance of missing doses. Your prescriber will guide you on exact timing when you start treatment.
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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 Day
You have complete flexibility in choosing when to take your Mounjaro dose each week. Some people prefer Monday morning so they start the week with their injection completed. Others choose Friday evening to build it into a weekend routine. The actual time of day doesn't matter — morning, afternoon, or evening all work equally well, and food intake doesn't affect how Mounjaro works.
What matters most is consistency. If you inject every Monday at 8am, your body adapts to that weekly rhythm. If you inject every Friday at 6pm instead, that's equally effective — as long as you stick with it. Set a phone reminder for your chosen day to help you remember, especially during the first few months when the routine is new.
Mounjaro comes in a pre-filled KwikPen device containing four weeks of doses. Each pen delivers one dose (between 2.5 mg and 15 mg depending on your titration stage). Store unopened pens in the fridge at 2–8°C, and once you've started a pen, you can keep it at room temperature (below 30°C) for up to 30 days.
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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.
Missing a Dose and Adjusting Your Schedule
If you miss your Mounjaro injection, take it as soon as you remember if it's within 4 days of your scheduled dose. Then continue with your normal weekly schedule the following week. If more than 4 days have passed, skip that dose and take your next injection on your normal scheduled day — never double up.
There must be at least 72 hours (3 days) between injections. If you need to change your regular injection day for any reason, inform your prescriber first. Some people switch their injection day seasonally or when their routine changes (holidays, work schedules). Your GP or weight management service can advise on safe scheduling adjustments. Track your weight progress using our free progress tracker to monitor how consistent timing supports steady results.
- 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 Mounjaro need to be taken at a specific time of day?
No. Mounjaro can be injected at any time of day — morning, afternoon, or evening. Food doesn't affect how it works either. The important thing is choosing a day you can stick with consistently, like every Monday or every Friday.
Can I change my Mounjaro injection day if needed?
Yes, but discuss any changes with your prescriber first. You might switch days if your routine changes, but you need at least 72 hours between injections. Your GP can help you plan a new schedule safely.
What happens if I miss a Mounjaro dose?
If you remember within 4 days, inject immediately and continue your normal schedule the next week. If more than 4 days have passed, skip it and take your next dose on your regular day. Never take a double dose.
Should I inject Mounjaro before or after meals?
Neither — meal timing doesn't matter. Mounjaro works the same whether you inject before, during, or after eating. Choose whatever time fits your routine best and remember it consistently.
Is it better to inject Mounjaro at the same time each week?
Yes, consistency helps. Injecting at roughly the same time on the same day each week makes it easier to remember and builds a predictable routine. Use a phone reminder to help establish the habit. ```
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.