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 Many Calories Should You Have on Mounjaro?
There's no fixed calorie target that applies to everyone taking Mounjaro. Instead, calorie intake should be individualised based on your starting weight, height, activity level, and health goals — ideally guided by your prescribing healthcare team. Mounjaro (tirzepatide) works by reducing appetite and increasing satiety, meaning you may naturally eat fewer calories without strict counting. However, Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity. Your GP or prescriber should discuss a realistic, sustainable calorie target with you during your initial assessment and ongoing care.
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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.
Calorie Deficits and Weight Loss on Mounjaro
For sustainable weight loss, the NHS recommends a calorie deficit of approximately 500 kcal per day, which typically results in losing around 0.5 kg per week. However, Mounjaro changes how much you naturally want to eat — many people report significantly reduced appetite without conscious restriction.
Clinical trials showed that people taking Mounjaro achieved average weight loss of 15–21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. This suggests the medication facilitates weight loss across a range of calorie intakes, rather than requiring a specific number.
Important: Very low calorie diets (under 800 kcal daily) should only be followed under medical supervision. Your prescriber or a registered dietitian can help you establish a calorie target that balances effectiveness with long-term sustainability, especially if you have type 2 diabetes or other weight-related health conditions requiring careful monitoring.
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.
Practical Calorie Guidance While on Mounjaro Treatment
Rather than aiming for a rigid calorie target, focus on eating nutrient-dense whole foods — lean proteins, vegetables, wholegrains, and healthy fats — which naturally support satiety and reduce overall intake. Many people on Mounjaro find they feel full on smaller portions, which naturally creates the calorie deficit needed for weight loss without constant counting.
Track your progress using our free progress tracker to monitor weight changes over time, then adjust portion sizes or meal frequency based on real results rather than theoretical targets. If you experience nausea or other side effects affecting your appetite, speak to your prescriber — dose adjustments or timing changes may help. Staying hydrated and including regular physical activity helps optimise results regardless of exact calorie intake, and your GP can refer you to a dietitian for personalised nutrition support if needed.
- 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.
Do I need to count calories strictly on Mounjaro?
No — Mounjaro reduces appetite naturally, so many people achieve weight loss without strict calorie counting. However, combining the medication with a reduced-calorie diet and physical activity gives better results. A registered dietitian can help you establish sustainable eating patterns rather than rigid calorie targets.
What calorie deficit should I aim for on Mounjaro?
The NHS recommends a deficit of around 500 kcal per day for steady loss of approximately 0.5 kg per week. However, your prescriber may recommend a different target based on your individual health, weight, and any comorbidities like type 2 diabetes. Discuss this during your clinical assessment.
Can I eat normally while taking Mounjaro?
Mounjaro works by suppressing appetite, so many people naturally eat less without feeling restricted. "Normal" eating typically means smaller portions that feel satisfying due to the medication's effects. Your prescriber should advise on realistic dietary changes based on your current habits and health goals.
What if I'm not losing weight despite Mounjaro and calorie reduction?
Weight loss varies between individuals. Factors include starting weight, underlying health conditions, medication adherence, physical activity, sleep quality, and stress levels. If you're not seeing expected progress, speak to your prescriber — they may suggest a dose increase, dietary adjustments, or investigation of other factors affecting loss.
Is Mounjaro effective without diet and exercise changes?
Clinical trials showed Mounjaro works best combined with a reduced-calorie diet and increased physical activity. While the medication reduces appetite, sustainable weight loss and health benefits require lifestyle changes. Your GP or prescriber can discuss realistic dietary and activity goals suited to your circumstances.
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.