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 Much Mounjaro Is in Each Dose?
Mounjaro doses are not measured in millilitres — each pre-filled KwikPen delivers a fixed dose of tirzepatide (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg) as a once-weekly injection. Unlike some medications, you don't measure Mounjaro by volume. This makes it simpler than older weight loss injections, and the KwikPen auto-delivers the correct amount each time. If you're comparing Mounjaro to Wegovy or wondering about prescription weight loss options available in the UK, understanding how doses work is important before speaking with your prescriber.
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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 Strengths vs Wegovy — How They Differ
Mounjaro (tirzepatide) comes in six dose strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. Each pre-filled KwikPen automatically delivers the exact dose — no ml measurement needed. You inject once weekly, and the medication is absorbed over seven days. The starting dose is 2.5 mg, with increases every four weeks if needed, up to a maximum of 15 mg.
Wegovy (semaglutide) uses a different dose range: 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, and 2.4 mg. It also comes as a pre-filled pen, delivered once weekly. SURMOUNT trial data showed Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy activates GLP-1 only — this mechanism difference means equivalent doses are not directly comparable between the two.
Both medications are prescription-only in the UK, require a clinical assessment before use, and are administered via once-weekly injection. Individual suitability depends on your health profile and prescriber assessment.
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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.
Choosing Between Mounjaro and Wegovy — What Your Prescriber Will Consider
Neither Mounjaro nor Wegovy is inherently "better" — the choice depends entirely on individual circumstances. Your GP or specialist may recommend one over the other based on your medical history, current medications, comorbidities like type 2 diabetes, and how you respond to treatment. Some patients find one more effective than the other; results vary significantly. Both require a reduced-calorie diet and increased physical activity to work effectively. If you're considering either medication, use our free GLP-1 weight loss calculator above to understand potential outcomes, then discuss eligibility with your prescriber. Access in the UK is through NHS specialist services (where available) or private online prescribing.
- 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 isn't Mounjaro measured in millilitres like other injections?
Mounjaro comes in pre-filled KwikPens that deliver a fixed dose by weight (mg), not volume (ml). This is safer and more precise than measuring liquid by volume. The medication concentration varies between doses, so ml amounts would be different for each strength — the mg system simplifies this.
What's the difference between Mounjaro's dose scale and Wegovy's?
Mounjaro ranges from 2.5 mg to 15 mg weekly. Wegovy ranges from 0.25 mg to 2.4 mg weekly. Approximate equivalence: Mounjaro 5 mg ≈ Wegovy 0.5 mg, Mounjaro 10 mg ≈ Wegovy 1.7 mg, Mounjaro 15 mg ≈ Wegovy 2.4 mg. However, clinical equivalence is not established — prescribers assess suitability individually.
How long does one Mounjaro KwikPen last?
Each KwikPen contains four doses — enough for four weeks of treatment. You inject once weekly, so one pen lasts exactly one month. When you start a new dose strength during titration, you'll start a new pen for that dose.
Can you switch from Mounjaro to Wegovy, or vice versa?
Switching between medications should only happen under prescriber guidance. There's no established direct conversion chart, though approximate dose equivalences exist. Your prescriber will assess whether a switch is appropriate and manage any transition carefully to avoid adverse effects.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are licensed in the UK for weight management. NHS access is through specialist tier 3/4 weight management services — not routine GP prescription. Private access is available through UK-licensed online prescribers following a clinical assessment. Availability and waiting times vary significantly by region.
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.