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 Deficit Calculator — How It Works in the UK
A calorie deficit is essential for weight loss, but understanding how much you need to lose and how Mounjaro (tirzepatide) supports that goal can be challenging. Our calorie deficit calculator helps you estimate the daily calorie reduction needed to achieve your weight loss targets, whilst our GLP-1 weight loss calculator shows how prescription weight loss medication like Mounjaro may support your efforts alongside diet and exercise. Whether you're considering Mounjaro through NHS specialist services or exploring private prescription options in the UK, understanding the maths behind sustainable weight loss is the first step to success.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Calorie Deficit Works With Mounjaro — NHS Context
A calorie deficit occurs when you consume fewer calories than your body burns, creating the conditions for weight loss. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week, which typically requires a deficit of around 500 kcal per day. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works alongside calorie reduction—it is not a replacement for dietary changes.
When you reduce your calorie intake and take Mounjaro, the medication may help by:
- Reducing appetite and food cravings
- Supporting feelings of fullness after smaller meals
- Slowing gastric emptying (how quickly food leaves your stomach)
- Helping regulate blood sugar and fat utilisation
In the SURMOUNT-1 clinical trial, patients on the maximum 15 mg dose achieved an average weight loss of around 21% body weight over 72 weeks—but this was alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Your GP or a prescriber can assess whether Mounjaro is suitable for your specific circumstances.
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.
NHS vs Private Access to Mounjaro in the UK
NHS route: Mounjaro is approved by NICE for use within NHS specialist tier 3 and tier 4 weight management services. Access requires a referral from your GP and assessment by a specialist team. Availability varies by region and ICB, and waiting lists can be lengthy in many areas. Once approved, your prescriber will manage your KwikPen doses and monitor your progress.
Private route: Mounjaro is available through UK-licensed private prescribers via online consultation, dispensed by GPhC-registered pharmacies. This route does not require NHS referral and is typically faster, though costs apply—usually £129–£320 per month depending on dose.
Whichever route you choose, a calorie deficit remains essential. Use our free BMI calculator to establish your current health baseline, and our GLP-1 weight loss calculator to project potential outcomes at different Mounjaro 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.
How much of a calorie deficit do I need for weight loss?
The NHS recommends a deficit of around 500 kcal per day for safe, sustainable weight loss of approximately 0.5 kg per week. This can be achieved through a combination of reduced food intake and increased physical activity. Very rapid deficits (over 1.5 kg per week) should only be undertaken under medical supervision and are not recommended long-term.
Does Mounjaro replace the need for a calorie deficit?
No. Mounjaro works alongside calorie reduction and exercise, not instead of them. In clinical trials, weight loss was achieved when patients combined Mounjaro with a reduced-calorie diet and physical activity. The medication supports your efforts by reducing appetite and helping you feel fuller, making it easier to maintain a deficit.
How is Mounjaro prescribed through the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services following a GP referral. Your GP will assess whether you meet eligibility criteria (BMI ≥30 or BMI 27–29.9 with weight-related health conditions). Access varies by region—some areas have shorter waiting lists than others. NICE guidance supports its use in appropriate cases.
What is the starting dose of Mounjaro, and how does it increase?
Mounjaro starts at 2.5 mg weekly for the first 4 weeks. The dose then increases every 4 weeks—5 mg, 7.5 mg, 10 mg, 12.5 mg—up to the maximum of 15 mg weekly. Your prescriber manages dose titration and may adjust based on your response and any side effects. Each KwikPen contains 4 weekly injections.
Can I calculate my weight loss projection with Mounjaro?
Yes. Our free GLP-1 weight loss calculator on this page can help you estimate potential weight loss at different Mounjaro doses based on clinical trial data. Remember that individual results vary considerably—the calculator provides a realistic range, not a assures. Always discuss expectations with your prescriber.
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.