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 I Eat On Mounjaro vs Wegovy?
When starting Mounjaro (tirzepatide) or Wegovy (semaglutide), many people wonder how much they should eat and whether calorie counting is still necessary. The answer depends on how each medication works, your individual response, and your prescriber's guidance. Both are prescription-only weight loss injections licensed in the UK, but they use different mechanisms — which can affect your appetite and calorie needs differently. Understanding the differences helps you manage your diet more effectively alongside whichever medication is prescribed for you.
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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: Appetite and Calorie Effects
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, which means it works on two hormone pathways. This dual action may produce stronger appetite suppression than single-mechanism medications, potentially leading to naturally lower calorie intake without strict counting.
Wegovy (semaglutide) is a GLP-1 receptor agonist only. Clinical trial data shows both medications reduce appetite and food cravings, but the mechanisms differ slightly. Based on SURMOUNT trial data for Mounjaro and STEP trials for Wegovy, both result in meaningful weight loss when combined with a reduced-calorie diet and increased physical activity.
- Mounjaro may suppress appetite more intensely due to dual-pathway activation
- Wegovy provides single GLP-1 pathway activation
- Individual responses vary significantly — some people feel fuller on less food, others maintain more appetite
- Both medications slow gastric emptying, extending feelings of fullness
Your prescriber or a registered dietitian can advise on appropriate calorie targets based on your dose, response, and health goals during your dose titration phase.
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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.
Calorie Intake Guidance: Both Medications Require Dietary Support
Neither Mounjaro nor Wegovy works without dietary change. Clinical trials showing weight loss success all involved participants following a reduced-calorie diet. Most UK prescribers recommend a structured approach rather than rigid calorie counting.
A typical starting point is a 500 kcal per day deficit from your estimated maintenance level, which may lead to approximately 0.5 kg weight loss per week. However, as your appetite naturally reduces on medication, you may find yourself eating less without deliberately restricting — this is the intended effect.
Use our free GLP-1 weight loss calculator to estimate potential weight loss projections at different doses. Pair this with the BMI calculator to track your progress against NHS healthy weight thresholds. Your GP or prescriber can provide personalised guidance based on your individual health profile and how you respond to 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.
Do I need to count calories on Mounjaro or Wegovy?
Not strictly, though structured dietary awareness is important. Both medications reduce appetite naturally, but they work best alongside a healthy, reduced-calorie diet. Many people find they naturally eat less without rigid counting — focus on balanced, nutritious meals rather than precise calorie totals. Your prescriber or dietitian can advise on whether formal calorie tracking is needed for your situation.
Will I eat significantly less on Mounjaro than Wegovy?
Possibly. Mounjaro's dual GIP and GLP-1 mechanism may produce stronger appetite suppression than Wegovy's single GLP-1 pathway. However, individual responses vary enormously — some people feel equally satisfied on either medication, while others experience more dramatic appetite reduction on Mounjaro. Your personal response depends on genetics, dose, and other health factors. Only experience with your prescribed medication will show your individual outcome.
How does the GLP-1 weight loss calculator help with calorie planning?
Our free GLP-1 calculator estimates potential weight loss at different Mounjaro and Wegovy doses based on clinical trial data. This helps you set realistic expectations and plan your health journey. Combine it with our BMI calculator to track progress against NHS healthy weight ranges. Results vary individually, but the calculator provides a realistic framework for discussion with your prescriber.
What calorie deficit should I aim for on these medications?
A typical starting point is a 500 kcal per day deficit from your estimated maintenance needs, targeting approximately 0.5 kg weekly loss. However, many people naturally eat less on medication without deliberate restriction — listen to your body. Your GP or a registered dietitian can assess your individual needs and adjust recommendations based on your response, dose titration progress, and health goals.
Are Mounjaro and Wegovy available on the NHS for weight management?
NICE has approved both medications for NHS weight management services. Access is through tier 3 specialist weight management services — not standard GP prescription. NHS availability and waiting times vary significantly by region. Private prescription is available through UK-licensed prescribers via online assessment. Both require clinical evaluation of eligibility based on BMI and health conditions before prescription.
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.