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
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Mounjaro Calorie Calculator — NHS UK Context
Understanding how Mounjaro (tirzepatide) works with calorie intake and weight loss is important for UK adults considering this prescription weight management option. This guide explains how Mounjaro supports a reduced-calorie diet, NHS eligibility criteria, and what to expect during dose titration. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different Mounjaro doses, alongside the BMI calculator to check your starting point and eligibility for NHS or private prescription routes in the UK.
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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 Calorie Intake and Weight Loss
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways that regulate appetite and energy balance. It works by reducing hunger signals, helping you feel fuller after smaller meals, and slowing how quickly food leaves your stomach. This allows you to maintain a calorie deficit more comfortably without extreme restriction.
Clinical trial data shows that participants on Mounjaro alongside a reduced-calorie diet lost an average of 15–21% of their body weight over 72 weeks, depending on the dose. However, individual results vary significantly. The medication does not create weight loss on its own — it supports lifestyle changes by reducing appetite, making it easier to stick to a lower-calorie eating pattern. The NHS dose titration schedule (starting at 2.5 mg, increasing weekly by 2.5 mg increments to a maximum of 15 mg) allows your body to adjust gradually while your prescriber monitors your response and any side effects.
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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.
NHS Eligibility and Prescribing Routes in the UK
NHS access to Mounjaro is through specialist tier 3 weight management services — not standard GP prescription. You must be referred by your GP and assessed by a specialist multidisciplinary team. Eligibility includes adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions (diabetes, hypertension, sleep apnoea, or cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower thresholds due to higher metabolic risk.
Private prescribing is also available through UK-licensed online services following a clinical assessment. Both routes require a prescription from a qualified healthcare professional. Use our free BMI calculator to check your starting BMI and consider discussing referral options with your GP. Your calorie targets should be personalised by your prescriber or dietitian, not generalised online.
- 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 work without calorie restriction?
No. Mounjaro supports weight loss alongside a reduced-calorie diet and increased physical activity. Clinical trials show it works best when combined with lifestyle changes. The medication helps reduce appetite so calorie restriction feels more manageable, but it is not a replacement for dietary changes or exercise.
How many calories should I eat while taking Mounjaro?
Your calorie target should be personalised by your prescriber, GP, or a registered dietitian — not based on online calculators. A typical target is 500 kcal/day below your maintenance level, creating approximately 0.5 kg loss per week. Your prescriber will adjust based on your individual health, metabolism, and response to the medication.
What is the NHS waiting time for Mounjaro through specialist services?
Waiting times vary significantly by region and local ICB (Integrated Care Board). Some areas have waits of several months to over a year. Demand currently exceeds NHS capacity. You can ask your GP about your local tier 3 service waiting time, or explore private prescribing options for faster access.
Can I get Mounjaro on the NHS if I am overweight but not obese?
Possibly, if your BMI is 27–29.9 kg/m² and you have at least one weight-related health condition (type 2 diabetes, prediabetes, hypertension, dyslipidaemia, or cardiovascular disease). Lower thresholds apply for South Asian and other high-risk ethnic groups. Your GP will assess your eligibility during the referral process.
How long does dose titration take on Mounjaro?
The standard NHS titration schedule takes approximately 16–20 weeks to reach the maximum 15 mg dose, increasing by 2.5 mg every 4 weeks. Your prescriber may adjust this schedule based on your tolerance and response. Once at maintenance dose, you continue once-weekly injections for as long as the medication remains appropriate for your health.
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.