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
How Often Do You Take Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection that you take once every week. It comes as a pre-filled KwikPen device and is injected under the skin. The exact dose increases gradually over time as your body adjusts, starting at 2.5 mg in your first week and potentially reaching a maximum of 15 mg. Your GP or prescriber will guide you through the dosing schedule and help you find the right dose for your individual needs. Each KwikPen contains four weekly doses, so you'll need a new pen every month.
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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.
Understanding the Mounjaro Dosing Schedule
Mounjaro follows a structured dose titration schedule — meaning the dose increases gradually over several weeks. You start at the lowest dose and move up every 4 weeks if your prescriber determines it's safe and appropriate for you.
- Weeks 1–4: 2.5 mg once weekly (starter dose)
- Weeks 5–8: 5 mg once weekly
- Weeks 9–12: 7.5 mg once weekly
- Weeks 13–16: 10 mg once weekly
- Weeks 17–20: 12.5 mg once weekly
- Week 21 onwards: 15 mg once weekly (maximum dose)
Not all patients reach the maximum dose — your prescriber may keep you at a lower dose if that's working well for you. The KwikPen is colour-coded by dose, making it easy to identify the correct dose each week. Each pen lasts four weeks, so you'll typically receive a new KwikPen every month from your pharmacy once you're established on treatment.
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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.
Injection Day Routine and Practical Tips
You can inject Mounjaro on any day of the week, but it's best to choose the same day each week for consistency — many people pick a day that's easy to remember, like Monday or Friday. You can inject at the same time of day, though timing flexibility is greater than with some other medications. The pen can be stored at room temperature (below 30°C) for up to 30 days after first use, making it convenient to carry. Inject into your stomach (abdomen), upper thigh, or upper arm, and rotate injection sites each week to avoid irritation. If you accidentally miss a dose, take it as soon as you remember within 4 days — if more than 4 days have passed, skip that dose and continue your normal schedule. Never take a double dose to make up for a missed injection.
- 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 on different days of the week?
Yes, you can inject Mounjaro on any day of the week. However, it's recommended to choose the same day each week to keep a consistent routine. For example, if you start on a Monday, aim to take your next dose the following Monday. If you need to change your injection day, discuss this with your prescriber or pharmacist first.
What happens if I miss a Mounjaro dose?
If you miss a dose, inject it as soon as you remember, provided it's within 4 days of your scheduled injection day. If more than 4 days have passed, skip that dose and take your next dose on your normal scheduled day. Ensure there's at least 72 hours (3 days) between doses. Never take a double dose.
How do I know if my Mounjaro dose is increasing?
Your prescriber will tell you when to move to the next dose level — typically every 4 weeks. Your KwikPen is colour-coded by dose, so you'll see a different colour pen when you move up. Your pharmacy will also confirm the new dose when dispensing. Always check the label on your pen before injecting to confirm the correct dose.
Can I take Mounjaro at different times of day?
Yes, Mounjaro can be injected at different times of day — timing flexibility is greater than with some other weight loss medications. However, it's helpful to choose a consistent time each week alongside your chosen injection day to build a routine and reduce the chance of missing doses.
Is Mounjaro prescribed through the NHS in the UK?
Mounjaro can be prescribed through NHS specialist weight management services (tier 3 tier 4), though availability varies significantly by region and waiting lists can be long. It's also available privately through GPhC-registered online pharmacies following a clinical assessment. Your GP can refer you to NHS specialist services, or you can pursue private prescribing — both require a prescription from a UK-licensed prescriber.
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.