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 Many ML in a Mounjaro Dose?
Mounjaro doses are not measured in millilitres (ML) — instead, they are measured in milligrams (mg) of the active ingredient tirzepatide. Each pre-filled KwikPen contains a specific dose of tirzepatide solution, but the actual volume injected varies slightly depending on the dose strength. In the UK, Mounjaro is available as a prescription-only weight management injection, with doses ranging from 2.5 mg to 15 mg once weekly. Understanding how Mounjaro dosing works is important if you're considering this treatment option.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro Doses and What They Contain
Mounjaro is dosed by milligrams (mg) of tirzepatide, not by injection volume. Each KwikPen contains 4 doses of a fixed concentration solution. The doses are:
- 2.5 mg — starting dose, weeks 1–4
- 5 mg — maintenance dose, weeks 5+
- 7.5 mg — escalation dose, weeks 9+
- 10 mg — escalation dose, weeks 13+
- 12.5 mg — escalation dose, weeks 17+
- 15 mg — maximum dose, week 21+
Each KwikPen is a pre-filled auto-injection device, and the exact ML volume varies by dose strength because the tirzepatide concentration differs. The 2.5 mg dose contains approximately 0.5 ML per injection, whilst the 15 mg dose contains approximately 3 ML per injection. However, what matters clinically is the mg dose, not the volume.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Mounjaro KwikPen Storage and Administration
Each Mounjaro KwikPen is a single-use, pre-filled injection device that contains 4 doses. The pen is supplied in a carton with a specific dose strength marked clearly. Unopened pens must be stored in a refrigerator at 2–8°C until use. Once you start using a pen, it can be kept at room temperature (below 30°C) for up to 30 days. After 30 days, unused pens must be disposed of safely. You do not need to measure or calculate volumes yourself — the KwikPen is pre-calibrated to deliver the correct dose automatically when you inject.
- 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 is Mounjaro measured in mg, not ML?
Tirzepatide (Mounjaro's active ingredient) is dosed by how much drug is in the injection, measured in milligrams. The volume (ML) varies because different dose strengths have different concentrations. Your GP or prescriber will specify the mg dose, and the KwikPen is pre-filled to deliver exactly that amount.
Does the KwikPen volume change as I escalate doses?
Yes, the injection volume increases as you move to higher mg doses. A 2.5 mg injection is approximately 0.5 ML, whilst a 15 mg injection is approximately 3 ML. This is normal and does not affect safety or efficacy — the KwikPen automatically delivers the correct volume for your dose.
What if I'm switching from another GLP-1 medication like Wegovy?
Mounjaro and Wegovy (semaglutide) are different medications with different mechanisms — Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy is a GLP-1 agonist only. Any switch between medications must be managed by your prescriber. Approximate equivalent doses exist (e.g. 10 mg Mounjaro ≈ 1.7 mg Wegovy), but this requires clinical oversight and cannot be done independently.
Can I refill a KwikPen, or do I need a new pen each month?
Each KwikPen is a single-use device containing 4 weekly doses (4 weeks supply). You cannot refill it. Once you've used all 4 doses, you will need a new KwikPen prescribed. Your prescriber or pharmacy will issue you a new KwikPen each month, or as directed.
Is Mounjaro available on the NHS, or only privately in the UK?
Mounjaro is available through both NHS specialist weight management services (Tier 3) and private online prescribing. NHS access requires referral to a specialist service and eligibility assessment based on BMI and weight-related health conditions. Private access is available following an online clinical assessment with a UK-licensed prescriber, though costs apply. Availability and waiting times vary 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.