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 Mounjaro Starting Dose?
The Mounjaro starting dose in the UK is 2.5 mg, administered as a once-weekly injection using a pre-filled KwikPen device. This initial dose is designed to allow your body to adjust to the medication and minimise side effects while your prescriber assesses your response. After 4 weeks on the starting dose, your prescriber may increase your dose if needed. Mounjaro is a prescription-only tirzepatide injection licensed for weight management in UK adults, and your GP or a qualified prescriber will determine the right dosing schedule 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 the Mounjaro Dose Titration Schedule Works
Mounjaro uses a dose titration schedule, meaning your dose increases gradually over weeks rather than starting at the maximum strength. Each dose is held for a minimum of 4 weeks before escalation to allow your body to adapt and your prescriber to monitor your response and any side effects.
- Weeks 1–4: 2.5 mg once weekly (starting dose)
- Weeks 5–8: 5 mg once weekly (first escalation)
- 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 maintenance dose)
Your prescriber may pause escalation at any dose if you experience significant side effects or if your response is satisfactory. Not all patients progress to the maximum dose.
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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.
Why Start at 2.5 mg and What to Expect
The low starting dose minimises nausea and gastrointestinal side effects, which are common when beginning a GIP and GLP-1 receptor agonist like tirzepatide. This gradual escalation approach helps your prescriber find your optimal dose — the dose that delivers the best weight management benefit whilst keeping side effects manageable for you personally.
In clinical trials, patients at the 15 mg dose (after full titration) achieved an average weight loss of approximately 21% of body weight, though individual results vary significantly. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses and track your progress with our free progress tracker throughout your treatment journey.
- 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 2.5 mg starting dose and go straight to a higher dose?
No. The 2.5 mg starting dose is mandatory in the UK dosing schedule. Starting at the lowest dose allows your body to adjust, helps your prescriber monitor your individual response, and reduces the risk of serious side effects. Skipping doses or increasing faster than recommended is not safe and is not supported by prescribing guidelines.
What if I don't tolerate the 2.5 mg starting dose well?
If you experience significant nausea, vomiting, or other side effects at the starting dose, inform your prescriber immediately. They may extend the duration at 2.5 mg beyond 4 weeks, reduce other contributing factors, or in some cases recommend stopping the medication. Never adjust doses yourself — always contact your prescriber first.
How is Mounjaro different from Wegovy in terms of starting dose?
Mounjaro (tirzepatide) starts at 2.5 mg weekly, whereas Wegovy (semaglutide) begins at 0.25 mg weekly. The difference reflects that tirzepatide is a dual GIP/GLP-1 agonist whilst Wegovy is a GLP-1-only medication. The two medications have different starting points and escalation schedules — any switch between them must be managed by your prescriber.
Will my GP prescribe Mounjaro, or do I need a specialist?
In the UK, Mounjaro is typically prescribed through specialist tier 3 weight management services via NHS referral, or through private online prescribing following a clinical assessment. NHS availability varies significantly by region and waiting times can be lengthy. Your GP can discuss referral options or suggest private pathways if NHS access is not available in your area.
Do I need to do anything special before starting the 2.5 mg dose?
Yes. Before starting Mounjaro, your prescriber will assess your medical history, current medications (especially oral contraceptives and diabetes medications), and check you are not pregnant. Inform them of any gallbladder, kidney, or pancreas problems. You'll receive training on how to inject, storage instructions, and what side effects to watch for.
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.