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 to Do If You Miss a Mounjaro Dose
If you've missed your weekly Mounjaro injection, the action you take depends on how many days have passed since your scheduled dose. Mounjaro is a prescription-only tirzepatide injection administered once weekly using a KwikPen device. If you miss a dose, you don't need to panic — clear NHS guidance exists for this situation. The key is understanding the 4-day window and knowing when to contact your prescriber. Whether you access Mounjaro through NHS specialist services or via private prescription, the missed dose protocol remains the same. This guide explains exactly what to do.
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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.
Missed Dose Guidance: The 4-Day Rule
Mounjaro's missed dose guidance follows a simple 4-day rule, aligned with NHS and NICE recommendations:
- Within 4 days of your missed dose: Take your injection as soon as you remember, then continue with your normal weekly schedule. This keeps you on track without disruption.
- More than 4 days since your missed dose: Skip the missed dose entirely and take your next dose on your normally scheduled day. Do not try to catch up with a double dose.
- Minimum time between doses: Always leave at least 72 hours (3 days) between injections. If fewer than 3 days have passed, wait until your normal scheduled day.
If you're unsure about timing, contact your prescriber or the NHS specialist team managing your Mounjaro treatment. They can confirm the correct action for your specific situation and adjust your schedule if needed.
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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.
NHS Access vs Private Prescriptions
If you access Mounjaro through NHS tier 3 specialist weight management services, your prescriber will provide written missed dose guidance when you start your tirzepatide course. NHS specialist teams also offer telephone support if you're unsure about what to do.
For those prescribed Mounjaro via private UK-licensed prescribers, the same missed dose rules apply — the medication works identically regardless of access route. However, support channels differ: NHS users contact their specialist clinic, while private users typically contact their prescribing service or pharmacy directly.
Whether your dose titration is managed through NHS services or private prescription, maintaining consistent weekly timing optimises weight loss results alongside reduced-calorie diet and physical activity.
- 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 happens if I miss a Mounjaro injection by one day?
If you remember within 4 days of your scheduled dose, take it as soon as you remember. You can then resume your normal weekly schedule from that new injection date. Always allow at least 72 hours (3 days) between doses. If in doubt, contact your NHS specialist team or prescriber for confirmation.
Can I take a double dose of Mounjaro if I miss one week?
No, never take a double dose of Mounjaro. If more than 4 days have passed since your missed dose, skip it entirely and take your next dose on your normally scheduled day. Taking extra Mounjaro increases the risk of side effects without benefit. Contact your prescriber if you need guidance.
How do I know if I'm eligible for Mounjaro on the NHS?
NHS NICE guidance approves tirzepatide for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Access is through specialist tier 3 weight management services, typically requiring GP referral. Eligibility criteria may be lower for South Asian, Chinese, Black African, or Black Caribbean adults. Ask your GP about local access.
Does missing a Mounjaro dose affect my weight loss progress?
Occasionally missing a dose is unlikely to significantly impact overall progress, especially if you catch up within the 4-day window. However, consistent weekly dosing with dose titration as planned typically produces the best results. If you regularly struggle with remembering doses, discuss reminder strategies with your prescriber.
Where can I get support if I'm unsure about my Mounjaro prescription?
If you're prescribed via NHS services, contact your specialist weight management clinic or call your GP practice. If prescribed privately through a UK-licensed prescriber, contact your prescribing service or pharmacy directly. You can also use our free GLP-1 weight loss calculator to track your progress and discuss questions with your healthcare team at your next appointment.
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.