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 Tirzepatide Works
Mounjaro (tirzepatide) doesn't directly "burn" fat in the way exercise does, but it works through a different mechanism to support weight loss. This prescription-only injection activates two natural hormone pathways—GIP and GLP-1—which help regulate appetite, reduce cravings, and support feeling fuller after smaller meals. In clinical trials, people taking Mounjaro alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight. Individual results vary significantly, and Mounjaro requires a clinical assessment before being prescribed. Use our free BMI calculator and GLP-1 weight loss calculator to understand your current health status and explore potential outcomes.
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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 works through a dual GIP and GLP-1 receptor agonist mechanism—different from single-action weight loss medications like Wegovy (semaglutide). Here's how it supports fat loss:
- Appetite regulation: Signals to the brain that you are satisfied with smaller portions, naturally reducing calorie intake
- Reduced cravings: Helps lower the urge to eat between meals, particularly for high-calorie foods
- Slower gastric emptying: Food moves through the stomach more slowly, extending the feeling of fullness (though this effect may reduce over time)
- Enhanced fat utilisation: The dual mechanism may improve how your body processes stored fat for energy
These effects occur alongside a reduced-calorie diet and physical activity—Mounjaro is not a standalone solution. Weight loss is achieved through the combined effect of reduced food intake, better appetite control, and lifestyle changes, not through direct "fat burning" like exercise provides.
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.
Mounjaro vs Other Weight Loss Options
Mounjaro (tirzepatide) differs from other UK-licensed weight loss medications. Compared to Wegovy (semaglutide), which uses only GLP-1, Mounjaro's dual GIP+GLP-1 action resulted in slightly higher average weight loss in clinical trials—approximately 20.9% body weight at the highest dose versus 14.9% for Wegovy. Both are prescription-only medicines requiring clinical assessment.
Access in the UK comes through either NHS specialist weight management services (tier 3 referral) or private prescribing following an online clinical assessment. Your GP or prescriber can advise on whether Mounjaro is suitable based on your BMI, health conditions, and medical history. Try our GLP-1 weight loss calculator to explore projected outcomes at different doses.
- 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 actually burn fat or just suppress appetite?
Mounjaro works primarily through appetite suppression and appetite regulation rather than direct fat burning. It signals fullness to the brain, reduces cravings, and slows stomach emptying—leading to reduced calorie intake. The weight loss comes from consuming fewer calories, not from the medication directly burning stored fat. Exercise and physical activity are what directly burn fat.
How much weight can you lose on Mounjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight over 72 weeks at the highest 15 mg dose, alongside a reduced-calorie diet and increased activity. Individual results vary significantly—some people lose more, others less. Results depend on dose, adherence, diet, exercise, and individual metabolism.
Is Mounjaro better than Wegovy for fat loss?
Clinical trials suggest Mounjaro may achieve slightly higher average weight loss (20.9% vs 14.9% for Wegovy), due to its dual GIP+GLP-1 mechanism versus Wegovy's single GLP-1 action. However, both are effective, and individual results vary. Your prescriber can advise which is more appropriate for your health profile and circumstances.
How quickly does Mounjaro start working?
Most people notice reduced appetite and appetite changes within the first 1–2 weeks, though some take longer. Weight loss typically becomes measurable after 4–8 weeks as the cumulative effect of reduced calorie intake takes hold. Doses are increased gradually (every 4 weeks) to minimise side effects and allow your body to adjust.
Can you use Mounjaro without changing your diet?
Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity. While the appetite-suppressing effects may lead to some natural calorie reduction, clinical trials showed results achieved alongside lifestyle changes. Your GP or prescriber will discuss diet and exercise expectations as part of your treatment plan.
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.