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
Serving Sizes for Weight Loss — UK Health Guidance
Serving sizes play a key role in weight management and controlling calorie intake for sustainable weight loss in the UK. Whether you're managing weight through dietary changes alone or considering prescription options like Mounjaro or Wegovy, understanding portion control helps support your health goals. The NHS recommends a calorie deficit of around 500 calories per day for steady weight loss of approximately 0.5 to 1 kg per week. Use our free BMI calculator to check your current weight status, and explore what serving sizes and portion control mean for your individual 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.
Prescription Weight Loss Options Available in the UK
For adults eligible for prescription weight management in the UK, medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) can support weight loss alongside reduced-calorie diet and increased physical activity. These GLP-1 and dual GIP/GLP-1 receptor agonist medications work by helping you feel fuller after smaller meals, which naturally supports better portion control and serving size management.
- Mounjaro: Dual GIP + GLP-1 injection, once weekly, doses from 2.5 mg to 15 mg. Clinical trials showed average weight loss of 15–21% of body weight.
- Wegovy: GLP-1 injection, once weekly, doses from 0.25 mg to 2.4 mg. Clinical trials showed average weight loss of approximately 15% of body weight.
- Saxenda: GLP-1 injection, once daily, doses from 0.6 mg to 3 mg. Available through NHS and private prescribing.
Eligibility includes a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Individual results vary, and prescription weight loss medications are always used alongside lifestyle changes.
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 Access vs Private Routes — How to Get Started
In the UK, you can access prescription weight management through two routes. The NHS route involves referral to a tier 3 specialist weight management service from your GP—availability varies significantly by region and waiting times can be lengthy. The private route involves a consultation with a UK-licensed prescriber via an online assessment, followed by prescription from a GPhC-registered pharmacy if clinically appropriate.
To find out if you're eligible for prescription weight loss medication, start by checking your BMI using our free BMI calculator above. Then speak with your GP about your weight management goals—they can discuss whether prescription medication, dietary support, or other interventions are suitable for you. Your GP can also refer you to specialist services if appropriate. Individual circumstances vary, so a personalised assessment is essential.
- 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 do serving sizes relate to weight loss?
Smaller, controlled serving sizes help create a calorie deficit—the key to weight loss. The NHS recommends losing 0.5–1 kg per week, which typically requires a deficit of around 500 calories daily. Serving sizes vary by food type; for example, a serving of protein is roughly the size of your palm, and a serving of grains is about a closed fist.
Can prescription weight loss medication help with portion control?
Yes. Mounjaro and Wegovy work partly by slowing how quickly food leaves your stomach and signalling fullness to your brain, which naturally helps you eat smaller serving sizes. This effect typically reduces over time, so combining medication with sustained dietary awareness is important for long-term success.
How do I know what serving sizes are right for me?
Use our free BMI calculator to check your current weight status, then discuss personalised portion guidance with your GP or a registered dietitian. For general NHS guidance on portion sizes, visit the NHS Eat Well website, which includes visual guides for different food groups.
Is prescription weight loss medication available on the NHS?
Yes, for eligible adults. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for use within NHS specialist weight management services (tier 3). Access varies by region; your GP can discuss whether you qualify and refer you to your local service.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP + GLP-1 receptor agonist (once weekly, up to 15 mg), while Wegovy is a GLP-1 agonist only (once weekly, up to 2.4 mg). Both support weight loss alongside dietary changes. Clinical trials showed Mounjaro averaged 15–clinically studied weight loss and Wegovy around 15%, though individual results vary significantly.
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.