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 or Wegovy?
When taking Mounjaro or Wegovy for weight management, calorie intake depends on your individual health, current weight, and prescriber guidance—not the medication alone. Both medications work alongside a reduced-calorie diet and increased physical activity. The NHS recommends a sustainable calorie deficit of around 500 kcal daily for typical weight loss of 0.5–1 kg per week. Your GP or weight management prescriber will give you personalised dietary advice based on your assessment. There's no universal "right" calorie level—it's tailored to you. Use our GLP-1 weight loss calculator to explore projected outcomes, and our BMI calculator to understand your current health baseline.
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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.
Clinical Trial Data: SURMOUNT vs STEP
Mounjaro and Wegovy achieved significant weight loss in clinical trials, but the studies did not prescribe exact calorie levels—instead, both groups followed reduced-calorie diets and increased physical activity. In the SURMOUNT-1 trial, Mounjaro (tirzepatide) at 15 mg helped participants lose an average of 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy (semaglutide) at 2.4 mg achieved approximately clinically studied weight loss over 68 weeks. Both medications reduce appetite and slow gastric emptying, which naturally lowers calorie intake without rigid restriction. The key difference: Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy targets GLP-1 only. This dual mechanism may explain slightly higher average weight loss with Mounjaro, though individual responses vary considerably. Neither trial enforced a specific calorie target—participants were advised on balanced, reduced-calorie eating.
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.
Calorie Needs and Individual Prescriber Guidance
A prescriber assessing you for Mounjaro or Wegovy will consider your current weight, metabolic rate, activity level, and health conditions to suggest a realistic calorie target. Typical guidelines: women may be advised 1,200–1,500 kcal/day, men 1,500–1,800 kcal/day, though this varies widely. Many people on GLP-1 or GIP/GLP-1 medications report naturally eating less due to reduced hunger—not from willpower alone, but from the medication's effects on appetite hormones. This means your actual calorie intake may drop without strict counting. A registered dietitian through NHS weight management services or private prescribers can provide personalised meal planning. Track your weight loss progress using our free progress tracker to see how your individual calorie intake is working for you.
- 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?
While calorie counting helps, many people naturally eat less due to reduced appetite from these medications. Your prescriber may suggest a calorie target (typically 1,200–1,500 kcal/day for women, 1,500–1,800 for men), but strict counting isn't always necessary. Focus on balanced, whole foods and listen to hunger cues—the medication helps regulate these naturally.
What's the difference between Mounjaro and Wegovy for calorie needs?
Both medications reduce appetite, so calorie needs are similarly reduced on either drug. Mounjaro (dual GIP+GLP-1) may produce slightly more appetite reduction than Wegovy (GLP-1 only) due to its dual mechanism, but individual variation is significant. Your prescriber tailors advice to you, not to the medication type.
Can I eat normally on these injections?
"Normally" changes on these medications. Most people find portion sizes naturally reduce because they feel fuller faster and stay satisfied longer. A standard meal may feel too large. This isn't restriction—it's the medication helping you eat appropriate amounts. This is why they work alongside dietary changes, not instead of them.
Will my prescriber tell me exactly how many calories to eat?
Yes, your GP or weight management prescriber should discuss a realistic calorie target during your assessment. This is personalised based on your health, goals, and lifestyle. Many also recommend working with a dietitian for detailed meal planning, especially available through NHS tier 3 weight management services.
How do Mounjaro and Wegovy affect metabolism?
These medications primarily work by reducing appetite and slowing stomach emptying—they don't directly boost metabolism. Weight loss comes from eating fewer calories (naturally, due to reduced hunger) and increased activity. Some evidence suggests GLP-1 agonists may preserve muscle during weight loss, which supports metabolic health long-term.
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.