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
Weight Loss Calorie Calculation & UK Medication Guide
To lose weight effectively in the UK, understanding calorie deficits is essential. The NHS recommends losing 0.5 to 1 kg per week, which typically requires a deficit of around 500 kcal per day. For many adults, sustainable weight management combines dietary changes with physical activity—and for those who are eligible, prescription weight loss medication can provide additional support. This guide covers how calories relate to weight loss, NHS eligibility criteria, and the prescription options available to you.
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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.
UK Prescription Weight Loss Options & Eligibility
Three prescription-only weight loss medications are currently licensed in the UK for weight management in adults: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are GLP-1 receptor agonists (or GIP/GLP-1 agonists in Mounjaro's case) that work by reducing appetite and helping you feel fuller after smaller meals.
You may be eligible for prescription weight loss medication if you have:
- A BMI of 30 kg/m² or above, or
- A BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea
Lower BMI thresholds apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage. In clinical trials, these medications helped participants lose an average of 15–21% of their body weight alongside reduced-calorie diet and increased physical activity—though individual results vary significantly.
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 & Next Steps
Access to prescription weight loss medication in the UK is available through two routes:
- NHS: Referral to a specialist tier 3 weight management service from your GP. Availability varies by region and waiting lists can be lengthy.
- Private: Online consultation with a UK-licensed prescriber through a GPhC-registered pharmacy. Available without NHS referral, though costs apply.
Start by speaking to your GP about whether you might be eligible. They can assess your BMI, health conditions, and discuss whether prescription weight loss medication is appropriate for you. Use our free BMI calculator above to check your current BMI, and try our GLP-1 weight loss calculator to see projected outcomes at different doses if you're interested in medication options.
- 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 many calories do I need to lose per day to lose weight?
The NHS recommends a calorie deficit of approximately 500 kcal per day for sustainable weight loss of around 0.5 kg per week. This can be achieved through a combination of dietary changes and increased physical activity. Very gradual weight management (more than 1.5 kg per week) is not recommended without medical supervision.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only injections licensed in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a maximum dose of 15 mg weekly. Wegovy (semaglutide) is a GLP-1 agonist only, with a maximum dose of 2.4 mg weekly. Clinical trial data shows both can support weight loss of 15–21%, though individual results vary. Your prescriber will assess which is more suitable for you.
Can I get weight loss medication through the NHS?
Yes, if you meet eligibility criteria and are referred to a specialist tier 3 weight management service by your GP. Availability varies significantly by region and ICB. Waiting lists can be several months or longer in many areas. You can also access prescription weight loss medication privately through an online prescriber if you prefer not to wait for NHS services.
What health conditions make me eligible for weight loss medication?
Common weight-related conditions that may qualify you include type 2 diabetes or prediabetes, high blood pressure, abnormal blood fats (dyslipidaemia), obstructive sleep apnoea, and a history of heart attack or stroke. Your GP or prescriber will assess your individual health circumstances to determine eligibility.
How does prescription weight loss medication work with calorie deficit?
Weight loss medications like Mounjaro and Wegovy work alongside, not instead of, dietary changes and physical activity. They help reduce appetite and food cravings, making it easier to maintain a calorie deficit. The medications are most effective when combined with lifestyle changes. Track your progress using our free progress tracker to monitor both weight and dietary changes.
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.