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 Do I Know If Mounjaro Is Working?
Knowing whether Mounjaro is working involves tracking multiple signs beyond the scales. Weight loss is the primary indicator, but appetite changes, energy levels, and how you feel in your clothes also matter. Unlike some medications, Mounjaro (tirzepatide) works gradually—meaningful results typically become noticeable after 4–12 weeks of consistent use. This guide explains what to expect, how to measure progress, and how Mounjaro compares to Wegovy in terms of effectiveness and timeline. Use our free GLP-1 weight loss calculator to estimate your potential progress at your current dose.
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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.
Signs Mounjaro Is Working — Clinical Markers vs Daily Changes
Weight loss is the primary indicator, though progress is gradual. In the SURMOUNT-1 clinical trial, participants on 15 mg Mounjaro lost an average of 20.9% of body weight over 72 weeks—results that varied significantly between individuals. By week 4–8, some people notice a small decrease (1–2 kg); by week 12, changes become more visible.
- Appetite suppression: You naturally eat less without feeling deprived
- Reduced cravings, especially for sugary or high-fat foods
- Feeling fuller on smaller portions
- Sustained energy without intense hunger between meals
- Clothes fitting differently or needing smaller sizes
These signs often appear before significant scale movement. Some people experience noticeable appetite changes within days; others take 2–3 weeks. This variation is normal—individual response depends on your starting weight, metabolism, diet, and exercise. Your prescriber will review your progress at regular check-ins, typically every 4 weeks during dose escalation.
Clinically BackedWeight Loss
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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 vs Wegovy — How They Compare in Effectiveness
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly GLP-1 receptor agonist injections licensed in the UK for weight management. The key difference: Mounjaro is a dual GIP and GLP-1 agonist, activating two hormone pathways, while Wegovy is a single GLP-1 agonist. In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% at maximum dose) compared to Wegovy (approximately 15% on average). However, individual response varies widely—some people achieve excellent results with Wegovy; others respond better to Mounjaro's dual mechanism. Your prescriber will assess which is more suitable based on your medical history, blood sugar control, and preferences. Both require a UK prescription and clinical assessment before starting.
Track your progress using our free progress tracker to log weekly weight changes, appetite levels, and how you feel. This helps you identify patterns and provides data for your prescriber at follow-up appointments. Calculate your personal BMI using our free BMI calculator to monitor changes in your BMI category alongside weight loss. If you're not seeing expected progress after 8–12 weeks on a stable dose, discuss this with your prescriber—you may benefit from a dose increase, or they may recommend switching to a different medication. Never stop or change your dose without medical guidance.
- 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.
How quickly will I see results with Mounjaro?
Most people notice appetite suppression within 1–3 weeks, though some experience this within days. Measurable weight loss typically becomes visible by week 4–8. However, results vary significantly—some individuals lose weight faster than others. SURMOUNT trial data showed average weight loss of 5–10% by week 16 on maximum dose, increasing to 20.9% over 72 weeks. Consistency with your reduced-calorie diet and physical activity accelerates results.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) activates only GLP-1. Clinical trials showed Mounjaro achieved slightly higher average weight loss (15–21%) versus Wegovy (approximately 15%), though individual responses vary. Both require UK prescription and clinical assessment. Your prescriber will recommend the most suitable option based on your health profile.
What if I'm not losing weight after 8 weeks on Mounjaro?
If progress is slower than expected, discuss this with your prescriber at your next review. You may benefit from a dose increase if you're not yet at the maximum 15 mg dose. Also check: Are you in a calorie deficit? Are you drinking enough water? Is stress or sleep affecting your progress? Sometimes progress is slower initially but accelerates after a few more weeks. Never adjust your dose independently.
Can I tell if Mounjaro is working without scales?
Yes. Early signs include reduced hunger and cravings (often the first change), feeling fuller on smaller portions, improved energy, clothes fitting better, and needing smaller sizes. Weight loss isn't the only measure of success—many people feel the medication is working based on appetite control alone. Track these subjective markers alongside weekly weigh-ins using our free progress tracker.
How does my dose affect how quickly Mounjaro works?
Mounjaro has five therapeutic doses: 2.5 mg (starting), 5 mg, 7.5 mg, 10 mg, and maximum 15 mg, with dose escalation every 4 weeks. Higher doses generally produce greater weight loss—the 15 mg dose showed the highest average loss (20.9%) in trials—but higher doses also increase side effects. You'll start low and escalate gradually. Your prescriber balances efficacy against tolerability for your individual needs.
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.