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
Do You Take Mounjaro Once A Week?
Yes, Mounjaro (tirzepatide) is administered as a once-weekly injection. In the UK, it's available as a pre-filled KwikPen device that you inject yourself each week, always on the same day. The dose starts at 2.5 mg and increases gradually over several weeks, with a maximum maintenance dose of 15 mg per week. Each KwikPen contains four weekly doses, meaning one pen lasts one month. It's a prescription-only medicine requiring a clinical assessment before you can begin treatment. Our GLP-1 weight loss calculator can help you understand potential weight loss projections at different Mounjaro doses.
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 Dosing Schedule — How Weekly Injections Work
Mounjaro is taken as a single injection once every seven days. You choose the same day each week—for example, every Monday—and stick to that schedule. The medication comes in a pre-filled KwikPen, which is designed for self-injection at home. Your prescriber will advise on the best injection sites: the stomach (most common), upper thigh, or upper arm.
The dosing follows a structured escalation plan:
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg
- Weeks 9–12: 7.5 mg
- Weeks 13–16: 10 mg
- Weeks 17–20: 12.5 mg
- Week 21+: 15 mg (maximum maintenance)
You stay on each dose for at least four weeks before increasing. This gradual approach helps your body adapt and allows your prescriber to monitor how you respond. If side effects occur, your dose may be adjusted or increased more slowly. Clinical trials showed that participants achieved an average weight loss of 15–21% of their body weight over 72 weeks—though individual results vary significantly and depend on diet and activity levels.
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 Access and Private Prescribing in the UK
In the UK, Mounjaro prescriptions come through two routes: NHS specialist services or private online prescribing. NHS access is through tier 3 specialist weight management services—you'll need a referral from your GP, and availability varies considerably by region. Waiting times for NHS specialist services can be lengthy in many areas.
Private route access is faster: you have an online consultation with a UK-licensed prescriber, and if clinically appropriate, a prescription is issued and dispensed by a GPhC-registered pharmacy. You must meet eligibility criteria: BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds. Check your eligibility using our free BMI calculator, and discuss options with your GP or a licensed prescriber.
- 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.
Is Mounjaro a weekly injection?
Yes. Mounjaro is injected once per week, always on the same day. It comes in a pre-filled KwikPen device containing four weekly doses (one month's supply). You inject it yourself at home into the stomach, thigh, or upper arm.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP+GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro achieved slightly higher average weight loss (15–21% vs 15%), though individual results vary. Your prescriber will assess which is suitable for you.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for use within NHS specialist tier 3 weight management services. Access requires a GP referral and varies by region. Many areas have long waiting lists. Private prescribing is available faster through online consultations with UK-licensed prescribers.
What happens if I miss a weekly Mounjaro dose?
If you miss a dose within four days, take it as soon as you remember and continue your normal schedule. If more than four days have passed, skip that dose and take your next injection on your normal scheduled day. Never take a double dose. Maintain at least 72 hours between injections.
How long do I need to take Mounjaro?
This depends on your individual response and prescriber guidance. Clinical trials ran for 72 weeks, but ongoing treatment may be considered if you're responding well. If you stop Mounjaro, weight may gradually return. Your prescriber will discuss long-term management and whether to continue, adjust, or stop treatment based on your progress and 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.