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 Is the Maximum Dose of Mounjaro?
The maximum dose of Mounjaro (tirzepatide) approved in the UK is 15 mg, taken once weekly as a pre-filled KwikPen injection. Most people do not start at the maximum dose—instead, treatment begins at 2.5 mg and gradually increases over several months based on how well the medication is working and how you tolerate it. Your prescriber will assess whether you need to reach the maximum dose or if a lower dose is more appropriate for your individual health needs.
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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 in the UK
Mounjaro dose escalation follows a structured schedule designed to help your body adjust to the medication gradually. Each dose is given once weekly as a pre-filled KwikPen injection containing four weeks of doses. You must stay on each dose for a minimum of four weeks before increasing to the next level, giving your prescriber time to assess your response and any side effects.
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first increase)
- Weeks 9–12: 7.5 mg (second increase)
- Weeks 13–16: 10 mg (third increase)
- Weeks 17–20: 12.5 mg (fourth increase)
- Week 21 onwards: 15 mg (maximum dose)
This escalation typically takes around five months to reach the maximum dose. However, your prescriber may stop increasing your dose at any level if you achieve good weight loss results and tolerate the medication well. Reaching 15 mg is not always necessary or appropriate for everyone.
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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.
When You Might Not Need the Maximum Dose
Clinical evidence shows that meaningful weight loss can occur at doses below the 15 mg maximum. In the SURMOUNT-1 trial, participants on 10 mg achieved approximately 19.5% average weight loss, while those on 15 mg achieved approximately 20.9%—a relatively modest additional benefit. Your prescriber may recommend staying at a lower dose if you experience good weight loss results, minimal side effects, or if higher doses cause tolerability issues such as persistent nausea or stomach problems. The aim is to find the dose that delivers the best balance of effectiveness and tolerability for your individual circumstances. Use our GLP-1 weight loss calculator above to explore potential outcomes at different doses.
- 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 skip the dose escalation and start on a higher dose?
No. Mounjaro must be started at 2.5 mg and escalated gradually every four weeks. This approach helps minimise side effects and allows your body to adjust to the medication. Starting at a higher dose increases the risk of severe nausea, vomiting, and gastrointestinal side effects.
Is the 15 mg maximum dose safe for all UK adults?
The 15 mg dose is approved in the UK for eligible adults, but individual safety and suitability are assessed by your prescriber based on your medical history, other medications, and how you tolerate lower doses. Some people may be advised to remain at a lower dose due to medical conditions or contraindications.
How long does it take to reach the maximum Mounjaro dose?
It typically takes approximately five months to escalate from the starting 2.5 mg dose to the 15 mg maximum, as you must stay on each dose for at least four weeks. However, escalation can be paused or stopped earlier if good results are achieved at a lower dose.
What if I experience side effects at a certain Mounjaro dose?
Inform your prescriber immediately. Common side effects (nausea, diarrhoea, constipation) often improve over time, but some people may not progress to higher doses if side effects are severe or persistent. Your dose may be reduced or remained at the current level.
Does a higher Mounjaro dose assures more weight loss?
Higher doses do support greater weight loss on average, but individual results vary significantly. Some people achieve satisfactory weight loss at 5 mg or 10 mg, whilst others may benefit from reaching 15 mg. Your prescriber will help determine the best dose for your response and goals.
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.