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
Mounjaro Pen Doses: What You Need to Know
Mounjaro (tirzepatide) is available as a once-weekly injection in a pre-filled KwikPen device. The medication comes in six different doses, starting at 2.5 mg and increasing to a maximum of 15 mg per week. Your prescriber will begin you on the lowest dose and gradually increase it over several weeks, depending on how well you tolerate the medication and your individual response. Understanding the dose schedule helps you manage your treatment effectively and know what to expect as your prescription progresses.
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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.
Mounjaro Dose Schedule and Titration
Mounjaro uses a gradual dose escalation process called titration. You'll start on the lowest dose and progress through a structured schedule:
- Weeks 1–4: 2.5 mg once weekly (initial adjustment dose)
- Weeks 5–8+: 5 mg once weekly (first maintenance dose)
- 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+: 15 mg once weekly (maximum maintenance dose)
You must spend at least four weeks on each dose before your prescriber increases it. This gradual approach allows your body to adjust and helps minimise gastrointestinal side effects. Your prescriber may also decide to keep you on a lower dose if it's working well for you—there's no requirement to reach the maximum dose. Try our GLP-1 weight loss calculator to see how different doses may compare in clinical trials.
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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.
KwikPen Storage and Practical Details
Each Mounjaro KwikPen contains four doses (a four-week supply) and is colour-coded by dose strength for easy identification. Unopened pens must be stored in a refrigerator at 2–8°C and kept in their original carton to protect from light—do not freeze them. After you first use a pen, it can be kept at room temperature (below 30°C) for up to 30 days. You'll rotate injection sites weekly between your stomach, upper thigh, or upper arm. Always dispose of your pen 30 days after first use, even if there's medication remaining. Your prescription leaflet provides detailed storage and injection instructions. Use our progress tracker to log when you've taken each dose and monitor how you feel week to week.
- 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.
Why does Mounjaro start at such a low dose?
The 2.5 mg starting dose allows your body to adjust to the medication and helps reduce nausea and other gastrointestinal side effects that may occur when you first start. Gradually increasing the dose over weeks gives your system time to adapt. Most people tolerate this approach well and can progress through the schedule without significant issues.
Can my prescriber skip doses or keep me on a lower dose?
Yes, absolutely. Your prescriber may decide to keep you on a lower dose like 5 mg or 7.5 mg if it's producing good results and you're tolerating it well. There's no requirement to reach the maximum 15 mg dose. The dose is personalised based on your individual response and health needs.
What if I miss a dose of Mounjaro?
If you miss a dose within 4 days, take it as soon as you remember, then continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next scheduled dose on your regular day. Never take a double dose. Ensure there's at least 72 hours (3 days) between injections.
How does Mounjaro compare to Wegovy dosing?
Mounjaro (tirzepatide) and Wegovy (semaglutide) have different dose ranges because they work through different mechanisms. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Mounjaro's maximum is 15 mg weekly; Wegovy's is 2.4 mg weekly. Clinical trials show different average weight loss outcomes—Mounjaro showed approximately 15–clinically studied weight loss, while Wegovy showed approximately 15% on average.
What should I do if I experience side effects at my current dose?
Contact your prescriber. They may recommend staying on your current dose longer, adjusting your diet, or occasionally reducing back to a previous dose. Most people find gastrointestinal side effects improve over time. Your GP or prescriber can provide personalised guidance based on what you're experiencing and your overall health.
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.