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
Calorie Deficit for Weight Loss — UK Guide
A calorie deficit is the foundation of sustainable weight loss, and prescription weight management options available in the UK can support this approach. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week, which typically requires a daily calorie deficit of around 500 kilocalories. For many UK adults, combining dietary changes with prescription weight loss medication may offer additional support. This guide explains how calorie deficit works, explores weight management options like GLP-1 injections, and helps you understand whether prescription treatment might be suitable for your situation.
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.
UK Prescription Weight Loss Options
Three prescription medications are licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist administered once weekly. Clinical trials showed participants lost an average of 15–21% of their body weight alongside a calorie-reduced diet.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. Evidence from clinical trials indicates an average weight loss of approximately 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection for weight loss, with longer availability in the UK market.
All three are prescription-only medicines that work by reducing appetite and helping you feel fuller after smaller meals. Eligibility depends on your BMI and weight-related health conditions. You can use our free GLP-1 weight loss calculator to explore potential weight loss projections, and our BMI calculator to check your starting point.
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 in the UK
NHS access: Mounjaro and Wegovy are available through specialist tier 3 weight management services, typically accessed via GP referral. Waiting lists vary significantly by region and can be several months or longer.
Private access: These medications are available through GPhC-registered online prescribing services following a clinical assessment. This route allows faster access without NHS waiting lists.
Either route requires a prescriber to assess your eligibility. Your GP can discuss which approach is most suitable and provide guidance on local NHS services. If you're considering treatment, track your progress using our free progress tracker to log results.
- 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 approximately 500 kilocalories per day to lose around 0.5 kg per week. This can be achieved through a combination of reduced food intake and increased physical activity. Very gradual weight management (more than 1.5 kg weekly) is not recommended without medical supervision.
Can weight loss medication replace calorie deficit?
No. Prescription weight loss medications like Mounjaro and Wegovy are designed to work alongside calorie reduction and exercise, not replace them. They help reduce appetite and cravings, making it easier to maintain a calorie deficit. Clinical trial results were achieved in combination with diet and activity changes.
Who is eligible for prescription weight loss medication in the UK?
Eligibility typically includes adults with a BMI of 30 or above, or 27 or above if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. A GP or licensed prescriber will assess whether treatment is suitable for your individual circumstances.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro is a dual GIP and GLP-1 agonist with slightly higher average weight loss outcomes (15–21%). Wegovy is a GLP-1 agonist only (average clinically studied weight loss). Both are once-weekly injections. The choice depends on individual health factors and prescriber recommendation.
Can I access weight loss medication through the NHS?
Yes, Mounjaro and Wegovy are available through NHS specialist weight management services (tier 3), but access varies by region and waiting times can be lengthy. Private online prescribing services offer faster access. Discuss both options with your GP to find the best route for you.
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.