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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What to Do If You Take Your Mounjaro Injection A Day Late
If you've taken your Mounjaro injection a day late, the good news is that a single day delay is generally not a cause for concern. Mounjaro is a once-weekly tirzepatide injection, and your body has flexibility in timing. However, understanding the correct guidance on missed or delayed doses is important for maintaining consistent results. Here's what the NHS and MHRA recommend for UK patients taking Mounjaro through NHS tier 3 weight management services or private prescription.
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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.
NHS Guidance on Mounjaro Dose Timing
Mounjaro is designed as a once-weekly injection, meaning you inject the same dose every 7 days. The MHRA product information states that if you've taken your dose a day late (within the typical weekly window), this is not a significant concern and does not require any action beyond continuing your normal schedule.
Key timing rules:
- If you remember within 4 days of your scheduled injection day, take the dose as soon as you remember, then continue your normal weekly schedule from that point
- If more than 4 days have passed, skip that dose and take your next injection on your normally scheduled day
- Never take two doses within 3 days (72 hours) of each other
- Minor delays of 1–2 days are not harmful and do not affect the effectiveness of your tirzepatide treatment
Your GP or prescriber can confirm this guidance at your next review. If you're receiving Mounjaro through an NHS specialist tier 3 weight management service, the clinical team will have given you specific injection day instructions during your assessment.
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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.
Maintaining Consistency With Your Mounjaro Schedule
The most important thing is to get back to your regular injection day as soon as possible. Write your injection day on your calendar or set a phone reminder to help prevent future missed doses. Many UK patients find it helpful to inject on the same day each week — for example, every Monday morning — to build it into their routine.
If you're concerned about a missed or delayed dose, contact your prescriber or the NHS weight management clinic that prescribed your Mounjaro. They can reassure you and provide personalised guidance. Using our GLP-1 weight loss calculator can also help you track your expected progress and spot any changes in your weight loss pattern that might be concerning.
- 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.
Is it dangerous to take Mounjaro a day late?
No. A single day delay is not dangerous and does not affect the safety or effectiveness of your treatment. Mounjaro is designed with flexibility in timing. The MHRA guidance allows delays of up to 4 days without requiring any change to your schedule. Continue with your normal weekly injection as planned.
Will taking Mounjaro a day late reduce its effectiveness?
No. A one-day delay will not significantly reduce effectiveness. Tirzepatide works over a full week in your system, so minor timing shifts don't impact results. What matters most is consistency over weeks and months. Get back to your regular schedule and continue as normal.
What should I do if I'm more than 4 days late with my Mounjaro dose?
If more than 4 days have passed since your scheduled injection day, skip that dose and take your next injection on your normally scheduled day. Never try to "catch up" with a double dose. Contact your prescriber if you're unsure — they can provide reassurance.
How can I remember to take my Mounjaro on time each week?
Set a phone reminder or alarm for your chosen injection day. Many UK patients inject on the same day each week (for example, every Monday). Write it on your calendar. If you're receiving Mounjaro through the NHS, your weight management clinic will have given you injection day guidance at your appointment.
Should I contact my GP if I take Mounjaro a day late?
No need to contact your GP for a single day delay — it's not a concern. However, if you repeatedly miss doses or have concerns about your injection schedule, contact your prescriber or NHS weight management service. They can help you manage your treatment and answer any questions about your tirzepatide prescription.
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.