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 Take Mounjaro a Day Late
If you've taken your Mounjaro injection a day late, don't worry — it's not an emergency. Mounjaro (tirzepatide) is a once-weekly injection, and being one day late is within a safe window. As long as it's within 4 days of your scheduled dose, you can take it as soon as you remember and continue your normal weekly schedule. If it's more than 4 days late, skip that dose and take your next injection on your regularly scheduled day. Always inform your GP or prescriber if you frequently miss doses, as consistency is important for managing your weight effectively with this medication.
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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 Missed Dose Guidance and Safety
Mounjaro (tirzepatide) is designed as a once-weekly injection, giving you flexibility if you're a day or two behind. Here's the official guidance:
- Within 4 days of your missed dose: Take the injection as soon as you remember, then continue your normal weekly schedule from that date
- More than 4 days since your missed dose: Skip that dose entirely and take your next injection on your normally scheduled day
- Minimum spacing: Ensure at least 72 hours (3 days) between doses to maintain safety
- Double dosing: Never take two doses at once to catch up
Your Mounjaro KwikPen allows you some flexibility, but consistency in your dose titration schedule is important for optimal results. If you frequently find yourself missing injections, discuss this with your prescriber — they may suggest strategies to help you remember, such as setting phone reminders or linking your injection day to another routine activity.
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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.
Mounjaro vs Wegovy: Key Differences in Dosing
When comparing Mounjaro (tirzepatide) and Wegovy (semaglutide), dosing schedules differ slightly. Wegovy follows a similar once-weekly injection pattern with the same 4-day forgiveness window for missed doses. However, the two medications work through different mechanisms — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Clinical trials show Mounjaro may achieve slightly higher average weight loss (around 15–21% body weight in SURMOUNT trials) compared to Wegovy (around 15% in STEP trials), though individual results vary significantly. Both require a UK prescription following clinical assessment, and your prescriber will determine which is more suitable for your health profile and eligibility.
- 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 take Mounjaro 1 day late?
Taking your Mounjaro injection 1 day late is safe and within normal tolerances. Simply take it as soon as you remember and continue your regular weekly schedule from that point. Mounjaro allows up to 4 days flexibility, so being 1 day late poses no risk to your treatment.
Can I take Mounjaro 2 days late?
Yes, 2 days late is still within the safe window. Inject as soon as you remember and resume your normal weekly schedule. The key is maintaining at least 72 hours (3 days) between doses and not exceeding the 4-day maximum delay before your next scheduled dose.
What if I'm more than 4 days late with my Mounjaro?
If more than 4 days have passed since your scheduled injection, skip that dose completely. Take your next injection on your normally scheduled day. Never try to catch up with a double dose — this risks side effects and inconsistent medication levels.
How does missed Mounjaro dosing compare to Wegovy?
Both Mounjaro and Wegovy follow the same missed-dose guidance — within 4 days, take it as soon as you remember; beyond 4 days, skip and resume your normal schedule. Both are once-weekly UK prescription injections requiring clinical assessment to determine which suits your health needs.
What should I do if I frequently miss my Mounjaro injections?
Contact your GP or prescriber if you're struggling to stay on schedule. They can help identify barriers to adherence and suggest practical solutions like phone reminders, linking your injection day to a routine activity, or discussing whether this medication is right for you at this 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.