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
What Time Is Best To Take Mounjaro?
Mounjaro (tirzepatide) is a once-weekly injectable medication, so timing is more flexible than daily medications. You can inject Mounjaro at any time of day that suits your routine — there is no specific "best time" from a clinical perspective. The key is choosing the same day and approximate time each week and sticking to it consistently. This helps you remember your weekly dose and maintain steady medication levels in your body.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Timing vs Wegovy — How They Compare
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly GLP-1 receptor agonist injections, so timing flexibility is similar for both. The main difference is not when you inject, but how you escalate doses: Mounjaro uses dose titration every 4 weeks (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg), whereas Wegovy escalates more gradually (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, 2.4 mg). Clinical trial data from the SURMOUNT and STEP trials showed that average weight loss ranged from 15–21% with Mounjaro and approximately 15% with Wegovy — individual results vary significantly regardless of injection time. Both require a UK prescription following clinical assessment.
- Choose a consistent day and time each week (e.g., every Monday morning)
- Set a phone reminder to help you remember your weekly dose
- Timing around meals does not affect how Mounjaro works
- You can inject at any time of day — morning, afternoon, or evening
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.
Choosing Your Injection Day — Practical Guidance
The best time to take your Mounjaro KwikPen is simply whichever day and time you are most likely to remember consistently. Many people choose a day linked to their routine — Monday morning with breakfast, or Friday evening. Your prescriber may recommend a specific time based on your dose titration schedule, particularly if you are escalating doses. If you miss a dose, you can inject within 4 days of your usual injection day and continue your normal schedule. After 4 days, skip that dose and inject on your next scheduled day. Try our free GLP-1 weight loss calculator to estimate potential outcomes with tirzepatide, and our BMI calculator to track how your weight and BMI progress over time with consistent treatment.
- 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 injecting Mounjaro?
No. Clinical guidance shows that any time of day is equally effective. What matters is choosing the same day and approximate time each week so you remember your dose consistently and maintain steady medication levels.
Should I take Mounjaro on an empty stomach or with food?
Mounjaro can be injected at any time — food does not affect how it works. Choose whatever time fits your routine best, whether that is morning, afternoon, or evening.
What's the difference between Mounjaro and Wegovy injection schedules?
Both are once-weekly injections with flexible timing. The main difference is dose escalation: Mounjaro escalates every 4 weeks, while Wegovy escalates more gradually. Neither requires a specific time of day.
What happens if I miss my Mounjaro injection?
If you remember within 4 days of your usual injection day, inject as soon as possible and continue your normal schedule. If more than 4 days have passed, skip that dose and inject on your normally scheduled day. Never take a double dose.
Can I change my Mounjaro injection day if I choose a different day?
Yes. You can change your injection day by choosing a new weekly day that suits you better. Inform your prescriber of the change, and maintain that new day consistently going forward.
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.