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 Is Best Time To Take Mounjaro?
Mounjaro is a once-weekly injection, and while there's no single "best time" mandated by MHRA or NHS guidance, consistency matters far more than the clock. Your tirzepatide dose should be injected at the same time each week to maintain steady hormone levels and track your progress effectively. This guide covers UK prescribing practice, dose timing, and practical advice from NHS and private prescribers.
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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 Timing: What the Guidance Says
The MHRA and NHS guidance for Mounjaro (tirzepatide) emphasises weekly consistency rather than a specific time of day. You can inject your KwikPen in the morning, afternoon, or evening—what matters most is choosing the same day and approximately the same time each week. This consistency helps you:
- Maintain steady levels of the medication in your bloodstream
- Track your injections reliably and avoid missed doses
- Monitor side effects and how your body responds week to week
- Build a sustainable routine you can stick to
Most UK prescribers recommend choosing a time that fits your lifestyle—perhaps Sunday evening when you meal plan, or Friday morning before work. The MHRA product information does not specify a preferred time of day, meaning flexibility is built into UK prescribing practice. If you miss your dose, take it within 4 days and resume your normal schedule the following week.
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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.
Practical Tips for Taking Your Weekly Mounjaro Dose
Set a phone reminder for your chosen day and time each week—this is the single most effective way to stay consistent. If you travel or your routine changes, adjust your injection time in advance rather than skipping a week. Store your Mounjaro KwikPen in the fridge until use (2–8°C), and allow it to warm to room temperature for a few minutes before injecting—this makes the injection more comfortable. Keep a simple log or use our free progress tracker to record your weekly injections alongside your weight and how you're feeling. If you experience severe side effects at a particular time of day (for example, nausea after breakfast), discuss timing adjustments with your prescriber, though the medication itself does not work better or worse based on meal timing.
- 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 it matter what day of the week I take Mounjaro?
No. The MHRA and NHS guidance do not specify a preferred day. What matters is choosing one day each week and sticking to it consistently. Many people choose Sunday, Friday, or Monday simply because these fit their routine—pick whichever day works best for you and set a weekly reminder.
Should I take Mounjaro with food or on an empty stomach?
Mounjaro can be taken regardless of meal timing. Unlike some oral medications, the injection is not affected by food in your stomach. Choose a time based on your routine and convenience, not meal timing. Some people prefer injecting before breakfast, others before bed—there is no clinical advantage to either.
Can I change my Mounjaro injection day if I need to?
Yes, but do it carefully. If you need to change your usual injection day, ensure at least 3 days (72 hours) pass since your last dose. Adjust your schedule in advance if possible. If you're unsure, contact your prescriber or the pharmacy that supplied your medication for guidance.
What should I do if I miss my weekly Mounjaro injection?
If you remember within 4 days (96 hours), inject as soon as you remember and continue with your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your normal scheduled day the following week. Never take two doses close together.
Is there a best time to start Mounjaro—morning or evening?
No clinical evidence suggests morning or evening injections work differently. Start at whatever time fits your lifestyle and allows you to be consistent. Evening injections suit people who prefer routine in the evening; morning injections suit early risers. Consistency matters far more than the time of day.
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.