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
When Should You Take Your Mounjaro Injection?
Mounjaro (tirzepatide) is a prescription-only once-weekly injection for weight management in UK adults. The timing of your Mounjaro dose is flexible — you can choose any day of the week that suits your routine, as long as you stick to the same day each week. Your prescriber will guide you on the specific dose you need based on your individual health assessment, and doses are gradually increased over several weeks. Understanding your dosing schedule helps you stay consistent with treatment.
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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.
How Mounjaro Dosing Works
Mounjaro is administered as a once-weekly injection, which you can take on any day you choose — there is no specific "best time of day" medically. You simply need to pick a day that works for your lifestyle and stick with it consistently. Your dosing schedule will follow a titration protocol, meaning your dose is gradually increased every four weeks from a starting dose of 2.5 mg up to a maintenance or target dose (typically 5–15 mg).
- Starting dose: 2.5 mg, weeks 1–4
- Week 5–8: 5 mg
- Week 9–12: 7.5 mg
- Week 13–16: 10 mg
- Week 17–20: 12.5 mg
- Maximum dose: 15 mg from week 21 onwards
Each KwikPen contains four weekly doses. Your prescriber will assess your response and any side effects before increasing to the next dose. You must stay on each dose for a minimum of four weeks before escalating.
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.
Practical Timing Tips and Consistency
The most important thing is consistency — taking your injection on the same day each week. Many people choose a day that's easy to remember, such as Monday morning or Friday evening. You can adjust your injection day if needed, but only once every four weeks, and you should space injections at least 72 hours (three days) apart to avoid overlap.
You can inject Mounjaro at any time of day — morning, afternoon, or evening — and you don't need to take it with or without food. Store unopened pens in the fridge at 2–8°C, and after first use you can keep a pen at room temperature (below 30°C) for up to 30 days. If you miss a dose within four days, take it as soon as you remember; if it's been longer than four days, skip that week and continue on your normal schedule.
- 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.
Can I take Mounjaro at different times on different weeks?
No. You should pick one day of the week and stick with it consistently. Consistency helps your body respond better and makes it easier to remember. You can change your injection day, but only once every four weeks, and space doses at least 72 hours apart.
Does Mounjaro need to be taken with food?
No. Mounjaro is an injection, not an oral tablet. You can inject it at any time, regardless of when you eat. Food does not affect how Mounjaro works. Some people find injecting before bed convenient; others prefer morning or afternoon — choose what suits your routine.
What if I miss my weekly Mounjaro injection?
If you remember within four days, take it as soon as you can and continue your normal schedule the following week. If more than four days have passed, skip that dose and take your next injection on your normal day. Never double up on doses. Contact your prescriber if you're unsure.
Can I switch my Mounjaro injection day?
Yes, but only once every four weeks. Ensure there are at least 72 hours (three days) between injections. Contact your prescriber if you need to make a significant change to your dosing schedule.
How do I know if my Mounjaro dose is right for me?
Your prescriber will assess your response at each four-week interval. They'll check your weight progress, any side effects, and your overall health before deciding whether to increase to the next dose. Use our free GLP-1 weight loss calculator to track your expected progress and discuss results with your prescriber at each review.
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.