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 Clicks for Half Dose Mounjaro?
The Mounjaro KwikPen is pre-filled with a specific dose — you cannot split doses or use partial clicks to achieve a half dose. Each KwikPen click delivers the full prescribed dose (typically 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg). If you need a half dose, your GP or prescriber will adjust your prescription to a lower dose tier rather than you attempting to self-split a dose. Understanding how the KwikPen works is essential for safe administration under NHS or private supervision.
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 KwikPen Dosing and Administration
The Mounjaro KwikPen is a pre-filled, single-dose injection pen designed to deliver a fixed amount of tirzepatide with each use. Each pen contains exactly one weekly dose — typically 4 pens per prescription box, lasting 4 weeks. The pen has a click mechanism, but it does not allow partial or half-dose administration. One full click = one complete dose. You cannot manually stop mid-click to achieve a reduced amount.
- Starting dose: 2.5 mg (given for weeks 1–4)
- Escalation doses: 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg (each given for minimum 4 weeks)
- Maximum dose: 15 mg once weekly
- Dose adjustment: Your prescriber adjusts your dose by issuing a new KwikPen prescription, not by splitting the current pen
If you require a half dose or dose modification, you must contact your GP or prescriber — they will reassess and potentially switch you to a lower-dose KwikPen entirely rather than attempting a UK pharmacy dose reduction.
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.
NHS Mounjaro Prescribing and Dose Adjustment
Under NHS prescribing guidelines, Mounjaro access typically occurs through specialist tier 3 weight management services following NICE approval. Dose titration (gradual escalation) is managed by your specialist team — you do not adjust doses yourself. If you experience side effects or feel a dose is too strong, your NHS team may recommend staying on your current dose longer, reverting to a previous dose, or pausing treatment before resuming. Your prescriber has access to your full medical history and can make safe, individualised decisions. Always report concerns to your GP or specialist rather than attempting to modify your injection technique or dose manually.
- 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 inject less than a full click on the Mounjaro KwikPen?
No. The KwikPen is designed to deliver one fixed dose per injection. You cannot safely split doses or use partial clicks. If you need a lower dose, your prescriber will issue a prescription for a lower-dose KwikPen instead. Never attempt to modify the injection manually.
What should I do if my current Mounjaro dose is causing side effects?
Contact your GP or prescriber immediately. They may recommend staying on your current dose longer, temporarily pausing treatment, or reverting to a previous dose. Dose adjustments must be made by your healthcare team, not by changing your injection technique.
How long does each Mounjaro dose stay at the same level?
NHS and clinical guidelines recommend staying on each dose for a minimum of 4 weeks before escalating. If you are tolerating your dose well and side effects are manageable, your prescriber may keep you on the same dose longer or until you reach your target weight.
Is Mounjaro available on the NHS for weight management in the UK?
Yes, Mounjaro (tirzepatide) is NICE-approved and available through NHS specialist tier 3 weight management services. Eligibility includes a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Availability and waiting times vary by region. You can also access Mounjaro privately through online prescribing if NHS services are not available locally.
What if I accidentally miss a week of Mounjaro?
If you miss your weekly injection, take it within 4 days of the scheduled date and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and resume on your regular day. Never take a double dose. Contact your prescriber or pharmacist for guidance if unsure.
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.