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 Often Do You Use Mounjaro?
Mounjaro (tirzepatide) is a once-weekly injection — you use it every 7 days on the same day each week. Unlike some older weight loss medications, you don't need daily injections or frequent clinic visits. Each Mounjaro KwikPen contains four weekly doses, so one pen lasts a month. The dose you inject increases gradually as your body adjusts, but the frequency stays the same throughout your treatment. Your GP or prescriber will show you how to inject it yourself at home.
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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 vs Wegovy: Injection Frequency and Mechanism
Both Mounjaro and Wegovy are once-weekly injections — a key advantage over older weight loss treatments. However, they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy (semaglutide) is a GLP-1 receptor agonist only, using a single mechanism.
In clinical trials, Mounjaro showed slightly higher average weight loss — around 15–21% of body weight depending on dose in the SURMOUNT trials — compared to Wegovy's average of around 15% in STEP trials. Both require the same once-weekly schedule, but the dosing ranges differ. Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg. Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg. Individual results vary significantly, and which medication is right for you depends on your personal 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.
Mounjaro Dosing Schedule and Titration
Your Mounjaro dose increases gradually over several months — a process called titration. You start at 2.5 mg for the first four weeks, then increase by 2.5 mg increments every four weeks until you reach your target dose or maximum tolerated dose. Throughout this process, the injection frequency remains once weekly. You'll always inject on the same day of the week.
Each KwikPen contains four pre-filled doses, lasting four weeks. You'll need a new pen each month. Your prescriber will decide your target dose based on your response and any side effects. Some people reach their therapeutic benefit at 5 mg or 10 mg; others continue to 15 mg. Calculate your potential weight loss at different doses using our GLP-1 weight loss calculator, and track your progress with our free progress tracker once you start treatment.
- 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 once a week or once a month?
Mounjaro is once a week — you inject it every seven days on the same day each week. One KwikPen contains four weekly injections, so one pen lasts a month. The weekly frequency remains consistent throughout your treatment, even as your dose increases.
Can you skip a week of Mounjaro?
No — Mounjaro works best when injected consistently once a week. If you miss a dose, inject it within four days of the missed injection day, then resume your normal weekly schedule. Never double-dose. Missing doses regularly can reduce effectiveness.
Which is better, Mounjaro or Wegovy?
Both are once-weekly injections licensed in the UK for weight management. Mounjaro uses a dual mechanism and showed slightly higher average weight loss in trials, but individual results vary. Your prescriber will assess which is more suitable based on your medical history, health conditions, and personal factors. Both require clinical assessment before prescription.
How long do you stay on Mounjaro?
Treatment duration varies individually. Some people use Mounjaro for 6–12 months; others continue longer. Your GP or prescriber will review your progress regularly and decide whether to continue, pause, or stop treatment based on your results and health goals. Stopping Mounjaro typically results in weight regain over time.
Can you switch from Wegovy to Mounjaro?
Yes — switching is possible and managed by your prescriber. While there's no official conversion chart, approximate equivalences exist (e.g. Wegovy 1.7 mg ≈ Mounjaro 10 mg). Any switch must be clinically supervised. Your prescriber will assess whether changing is appropriate for you and manage the transition safely.
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.