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's the Best Time to Take Mounjaro?
Mounjaro (tirzepatide) is a once-weekly prescription injection, and timing is flexible — you can inject on any day that works for you, as long as you maintain consistent weekly doses. Unlike daily medications, there's no specific "best time of day" since the injection delivers a full week's worth of medication at once. What matters most is choosing a day you'll remember and sticking to it. Your prescriber will advise you on the timing that fits your schedule and lifestyle.
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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.
Timing Flexibility and Consistency
The key principle with Mounjaro is consistency rather than specific timing. You can inject:
- In the morning or evening — whichever suits you
- Any day of the week you choose
- With or without food
- At the same time each week (e.g. every Monday at 6 pm)
Because Mounjaro is a once-weekly injection containing your full dose for seven days, the exact time within that day is not critical to how it works. What is important is maintaining weekly consistency. If you're supposed to inject on a Monday, injecting Monday morning or Monday evening makes no difference — but skipping to Wednesday would break your routine. Your prescriber may recommend a specific day based on your lifestyle, work schedule, or when you're most likely to remember.
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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.
Adjusting Your Injection Day
If you need to change your injection day, it's straightforward with Mounjaro. You can shift your scheduled day as long as your next injection is at least 3 days (72 hours) away from your last dose. For example, if you normally inject on Monday but need to move to Wednesday next week, that's fine — there's a 9-day gap between doses. However, you cannot inject twice within 72 hours. If you miss your scheduled injection, inject as soon as you remember (within 4 days of the missed date), then resume your normal weekly schedule. Your GP or prescriber can help you adjust your injection day if needed.
- 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.
Can I take Mounjaro at different times each week?
Yes. While consistency is important, the exact time within your chosen day is flexible. What matters is maintaining your weekly schedule — for example, "every Monday" rather than varying between Monday and Thursday.
Does food affect when I should inject Mounjaro?
No. Mounjaro can be injected with or without food. The injection works the same way regardless of whether you've eaten. You do not need to time it around meals.
What happens if I inject late or early by a few hours?
A few hours difference won't affect how Mounjaro works. The 72-hour gap rule applies to preventing double-dosing, not to minor timing variations within your chosen day.
Can I switch from morning to evening injections?
Yes. As long as you maintain seven days between doses, you can switch your preferred time. Just ensure your next injection is at least 72 hours after your previous one.
Should I always inject at the same time of day for best results?
Consistency helps with remembering your dose, but the exact time of day doesn't affect how Mounjaro works. Choose a time you'll remember and stick to it, whether that's morning or evening.
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.