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
Can You Take Mounjaro a Day Late?
Yes, you can take Mounjaro a day late without significant risk. Mounjaro is a once-weekly tirzepatide injection designed with some flexibility built in. If you miss your scheduled dose by a day or two, you can take it as soon as you remember, then continue your normal weekly schedule. However, the exact guidance depends on how many days have passed since your missed dose. This guide explains the NHS-recommended approach and how Mounjaro's dosing schedule compares to Wegovy.
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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 vs Wegovy: Missed Dose Guidance and Schedule Flexibility
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only once-weekly injections, but they have slightly different missed-dose protocols. For Mounjaro: if you miss a dose within 4 days of your scheduled injection date, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. For Wegovy: similar guidance applies — within 4 days, take it immediately; beyond 4 days, skip and resume your normal schedule. The key difference is that Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy is GLP-1 only. This means Mounjaro's appetite-suppressing effect may be slightly stronger, but neither medication requires rigid daily timing like some other injections. A minimum of 72 hours (3 days) must pass between doses — this is the safety threshold for both medications.
Clinically BackedWeight Loss
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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.
Individual Prescriber Guidance: Which Is Right for You?
Whether you're prescribed Mounjaro or Wegovy depends on your individual health profile, assessed during your clinical consultation. Both are available on the NHS through specialist tier 3 weight management services, though access varies significantly by region and waiting lists can be substantial. Privately, both are accessible through UK-licensed online prescribers following an assessment. NICE has approved tirzepatide (Mounjaro) for use within NHS specialist services. Clinical trial data showed Mounjaro users lost an average of 15–21% body weight, while Wegovy users lost approximately 15% on average — though individual results vary significantly. Your prescriber will consider your BMI, weight-related health conditions, other medications, and personal preferences when deciding which medication suits you best. Both require a prescription and ongoing monitoring.
- 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.
What should I do if I'm one day late with my Mounjaro injection?
If you're only one day late, inject as soon as you remember, then continue your normal weekly schedule. There is no need to double-dose or adjust your routine. Mounjaro is designed with a 4-day window of flexibility, so being a day late is well within safe limits.
Is there a maximum number of days I can be late taking Mounjaro?
Yes. You can be up to 4 days late with Mounjaro. If more than 4 days have passed since your scheduled injection date, skip that dose and take your next injection on your normal weekly day. Always maintain at least 72 hours (3 days) between injections for safety.
Does Mounjaro work differently than Wegovy if doses are delayed?
Both Mounjaro and Wegovy follow the same missed-dose protocol — within 4 days, take it; beyond 4 days, skip it. However, Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. This affects appetite suppression strength but not dosing flexibility. Your prescriber can advise which suits your circumstances.
What if I miss my Mounjaro injection by more than a week?
If more than 4 days have passed, skip the missed dose and inject on your normal scheduled day. If you've missed a full week or longer, contact your prescriber before your next injection. They may adjust your schedule or dose based on how long you've been off the medication. Never attempt to catch up with a double dose.
Can I use MyWeightCheck tools to track my Mounjaro progress if I'm adjusting my injection schedule?
Absolutely. MyWeightCheck's free progress tracker lets you log your weight consistently, and our GLP-1 weight loss calculator can help you project potential results with Mounjaro at different doses. Use the BMI calculator to monitor your BMI changes alongside your injection schedule — consistency in tracking matters more than perfect timing.
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.