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 I Take Mounjaro 2 Days Late?
If you've missed your Mounjaro (tirzepatide) injection by 2 days, you can still take it safely — this falls within the recommended window. Mounjaro is a once-weekly GLP-1 receptor agonist prescribed for weight management in the UK. Missing a dose by a couple of days shouldn't cause serious problems, but timing matters. This guide explains what to do if you're running late with your Mounjaro KwikPen injection and when you should contact your healthcare provider for guidance.
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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.
Mounjaro Missed Dose Guidance — The 4-Day Window
The key rule with Mounjaro is the 4-day window. If you're 2 days late, you're well within the safe zone and should take your injection as soon as you remember. According to the prescribing information and UK guidance, as long as it's been less than 4 days (96 hours) since your scheduled dose, you can administer it and then return to your normal weekly schedule.
Here's how to manage it:
- 1–4 days late: Take your injection as soon as you remember, then continue with your regular weekly schedule from that new date
- More than 4 days late: Skip that dose and take your next scheduled injection on your normal day
- Minimum gap: Always leave at least 72 hours (3 days) between doses — never inject twice within 3 days
For a more personalised view of your progress and dose management, you can track your injection schedule alongside weight changes using tools available through your prescriber's clinic or your own records.
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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.
What to Do If You've Missed Your Dose
Contact your GP or the prescriber who issued your Mounjaro prescription if you're unsure about timing — they know your full medical history and current dose schedule. If you're receiving Mounjaro through an NHS tier 3 specialist weight management service, your clinic will have specific guidance for missed doses. If you've obtained it through private prescribing, most online pharmacies or prescribing services provide written guidance with your KwikPen supply.
Never double-dose to make up for a missed injection. Stick to the standard guidance: take it within 4 days of your scheduled time, or skip and resume your normal schedule. If you frequently miss injections, speak with your prescriber about whether the weekly schedule is working for you.
- 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 safe to take Mounjaro 2 days late?
Yes, it's safe to take Mounjaro up to 4 days (96 hours) after your scheduled injection time. Two days is well within this window. Take it as soon as you remember, then resume your normal weekly schedule from that new date. There's no need to skip the dose or take extra.
What happens if I take Mounjaro more than 4 days late?
If more than 4 days have passed since your scheduled injection, skip that dose entirely and take your next dose on your normal scheduled day. Don't try to catch up with a double dose — this increases the risk of side effects and isn't necessary.
Can I inject Mounjaro twice in one week to catch up?
No. Never inject Mounjaro more than once per week. You must leave a minimum of 72 hours (3 days) between doses. If you've missed a dose by more than 4 days, simply skip it and wait for your next scheduled weekly injection.
Should I contact my GP if I've taken Mounjaro 2 days late?
You don't need to contact your GP for being 2 days late — this is within normal guidance. However, if you're frequently missing doses or worried about your injection schedule, contact your prescriber. They can offer advice tailored to your situation and check if the weekly schedule is working for you.
Does a late Mounjaro injection affect weight loss results?
Being 2 days late shouldn't significantly impact your weight loss results. Mounjaro's effects build up over weeks and months of consistent use. One missed injection or slightly late dose won't derail your progress. The key is returning to your regular schedule and maintaining consistency over time.
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.