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
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When Should You Take Mounjaro? Your UK Timing Guide
The best time to take Mounjaro is once every seven days on a day that suits your schedule — there is no specific time of day required. Unlike some medications, Mounjaro works as a once-weekly injection with flexibility in timing, though consistency helps. This guide explains Mounjaro injection scheduling, compares it to Wegovy's timing, and answers your questions about when to use your KwikPen. Try our GLP-1 weight loss calculator to explore how Mounjaro dose progression works alongside lifestyle changes.
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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.
Mounjaro Injection Timing and Schedule
Mounjaro can be injected at any time of day — morning, afternoon, or evening — as long as you choose a consistent weekly schedule. Unlike oral medications, time of day does not affect how tirzepatide works. The key is remembering to inject on the same day each week. Many people choose a day that fits their routine — for example, a Sunday evening at home, or a Monday morning — and stick with it. Each Mounjaro KwikPen contains four doses (four weeks' supply), so your schedule is entirely flexible. You can change your injection day if needed, as long as the gap between doses is at least 72 hours (three days). If you miss your usual day by a day or two, simply inject as soon as you remember and continue with your regular weekly cycle.
- Choose a day that fits your routine for consistency
- Inject at any time on your chosen day — time of day does not matter
- Minimum 72 hours (3 days) between doses
- Maximum 4 weeks between doses — if you miss a week, contact your prescriber
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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.
Mounjaro vs Wegovy — Injection Schedule Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly injections with flexible timing. The main differences are in how they work and dosing, not when you take them. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only — this affects the dose escalation schedule but not injection timing. Clinical trial data from SURMOUNT (Mounjaro) and STEP (Wegovy) trials both showed once-weekly dosing is effective. In UK NHS nice guidance and private prescribing, both are managed as simple once-weekly injections. Your prescriber will explain which might suit you based on your UK eligibility assessment and individual health circumstances. Neither requires injecting at a specific time — what matters is consistency in your chosen day.
- 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 time of day I inject Mounjaro?
No. Mounjaro can be injected at any time of day — morning, afternoon, or evening. Time of day does not affect how tirzepatide works. What matters is choosing a consistent day each week and sticking to it for easier remembering.
Can I change the day I take my Mounjaro injection?
Yes. You can change your injection day if needed, as long as there is at least 72 hours (three days) between doses. Inform your prescriber of any significant changes, but flexibility is built into Mounjaro dosing.
What happens if I miss my Mounjaro injection?
If you miss within 4 days of your usual day, inject as soon as you remember and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and inject on your normally scheduled day. Never double-dose.
Is Mounjaro injection timing different from Wegovy?
No. Both Mounjaro and Wegovy are once-weekly injections with flexible timing — you choose a day that suits you. The differences are in mechanism (dual GIP+GLP-1 for Mounjaro vs GLP-1 only for Wegovy) and dose escalation, not in when you inject.
Should I take Mounjaro with food or on an empty stomach?
Mounjaro is an injection, not an oral medication, so food does not affect it. You can inject regardless of whether you have eaten. Choose whatever time and day suits your routine best.
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.