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?
Yes, you can take Mounjaro up to 4 days late and still follow your normal weekly schedule — this tirzepatide injection is designed with a safety window. If you miss your weekly dose, timing within this window means you don't need to adjust your schedule. However, if you're more than 4 days late, you should skip that dose and return to your regular injection day. Always contact your prescriber or pharmacist if you're unsure, as individual circumstances vary.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Understanding the Mounjaro Dosing Window
Mounjaro is given as a once-weekly injection, and the medication is designed to work effectively even with minor timing variations. The prescriber information states that if you forget your weekly dose, you can take it within 4 days of the scheduled date without needing to change your normal schedule. This 4-day grace period exists because the tirzepatide molecule has a pharmacokinetic profile that tolerates this variation.
- 0–4 days late: Take the dose as soon as you remember, then continue your usual weekly schedule from the next planned date
- More than 4 days late: Skip the missed dose entirely and take your next dose on the normally scheduled day
- Minimum interval: Ensure at least 72 hours (3 days) between doses if you do take a late dose
This guidance applies regardless of whether you're taking Mounjaro for weight management or if you've been prescribed it for another indication. Never take a double dose to make up for a missed injection.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Miss Your Mounjaro Injection
If you realise you've missed your Mounjaro KwikPen injection, contact your prescriber or pharmacist immediately for guidance specific to your situation. They can confirm the exact timing and confirm whether you're within the 4-day window. If you're unsure of the exact date you were supposed to inject, your pharmacy records will show your scheduled injection dates.
For future doses, consider setting a phone reminder for your weekly injection day. Many people find it helpful to choose the same day each week — for example, every Monday morning — to establish a routine and reduce the risk of forgetting. If you're using your Mounjaro KwikPen correctly and storing it properly (refrigerated before first use, then at room temperature for up to 30 days), timing variations within the 4-day window will not affect the medication's effectiveness.
- 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 2 days late within the safe window for Mounjaro?
Yes, 2 days late is well within the 4-day grace period. You can take your dose and continue your normal weekly schedule from your next planned injection date. There's no need to adjust your dosing routine or skip a dose.
What happens if I take Mounjaro more than 4 days late?
If you're more than 4 days late, skip that missed dose and take your next injection on your normally scheduled day. Never take a double dose or try to "catch up" — this could increase side effects without improving results.
Will taking Mounjaro 2 days late affect my weight loss results?
No, taking your dose within the 4-day window will not compromise your weight loss progress. Tirzepatide is designed to work effectively with minor timing variations, so a 2-day delay will not impact your results.
Should I contact my GP if I miss a Mounjaro dose by 2 days?
You don't need to contact your GP for a 2-day delay, as this falls within the safe window. However, if you're unsure about timing or have concerns, contacting your prescriber or pharmacist is always a reasonable step. They can confirm whether you're within the safe window for your specific situation.
Can I use the GLP-1 weight loss calculator if I've missed a dose?
Yes, you can still use our GLP-1 weight loss calculator to track projected results. A single missed dose within the 4-day window won't significantly affect your overall weight loss trajectory. Use the calculator to estimate outcomes based on your current dose and continue as scheduled.
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.