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
Does Mounjaro Burn Fat? How It Works in the UK
Mounjaro doesn't directly "burn" fat in the way exercise does, but it may help your body use fat more effectively by reducing hunger and supporting a calorie deficit. This prescription-only medicine works by activating two natural hormone pathways—GIP and GLP-1—which help regulate appetite and food intake. In the UK, Mounjaro is prescribed through NHS specialist services or privately following clinical assessment. Understanding how it works helps you have realistic expectations about weight management with this medication.
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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.
How Mounjaro Affects Fat and Weight Loss
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, which sets it apart from single-mechanism medications like Wegovy. Rather than directly burning fat, Mounjaro helps create the conditions for fat loss by reducing appetite, lowering food cravings, and helping you feel fuller after eating less. In clinical trials (SURMOUNT-1), participants taking Mounjaro lost an average of 15–21% of their body weight over 72 weeks—though individual results vary significantly.
- The medication slows gastric emptying, meaning food stays in your stomach longer
- It reduces hunger signals to the brain, supporting adherence to a reduced-calorie diet
- It may improve how your body utilises fat for energy
- Weight loss requires both the medication AND lifestyle changes (diet and activity)
Real fat loss only happens when you consume fewer calories than you burn. Mounjaro makes this calorie deficit easier to achieve by reducing hunger, but it is not a substitute for dietary changes.
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 Eligibility and NHS Access in the UK
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. NICE has approved tirzepatide for use within NHS services, but access is limited and waiting lists can be very long in many regions. Private access is available through online prescribers and GPhC-registered pharmacies without NHS referral. Your GP can advise whether specialist referral is appropriate or discuss private options with you.
Track your progress and estimate potential weight loss outcomes using our free GLP-1 weight loss calculator, which projects results at different doses based on clinical evidence. You can also use our free BMI calculator to check whether you may be eligible for prescription weight loss treatment in the UK. Remember, any medication decision requires individual clinical assessment—neither Mounjaro nor other weight loss injections are suitable for everyone.
- 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.
Does Mounjaro burn fat directly?
No. Mounjaro doesn't actively burn fat like exercise does. Instead, it reduces appetite and helps you maintain a calorie deficit, which allows your body to use stored fat for energy. Real fat loss requires eating fewer calories than you burn—Mounjaro makes this easier by controlling hunger.
How much fat can you lose on Mounjaro in the UK?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, though individual results vary greatly. Weight loss depends on your starting weight, adherence to diet and activity changes, and personal metabolism. Your GP or prescriber can discuss realistic expectations for your situation.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro is NICE-approved for use through NHS tier 3 specialist weight management services if you meet eligibility criteria (BMI 30+ or 27–29.9 with health conditions). However, NHS availability is limited and varies by region. Private prescribing is also available without NHS referral.
What's the difference between Mounjaro and Wegovy for fat loss?
Mounjaro is a dual GIP and GLP-1 agonist; Wegovy is GLP-1 only. Mounjaro may produce slightly greater weight loss (15–21% vs ~15%), but both work by reducing appetite. Mounjaro has a maximum dose of 15 mg weekly; Wegovy's maximum is 2.4 mg. Both require prescription and clinical assessment.
Do I need to exercise and diet while taking Mounjaro?
Yes. Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity. Clinical trials showed results with lifestyle changes—medication alone won't produce sustained fat loss. Your GP or weight management service can advise on appropriate nutrition and exercise plans.
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.