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
Portion Sizes for Weight Loss in the UK
Portion control is one of the most practical ways to create a calorie deficit and support sustainable weight management in the UK. Reducing portion sizes doesn't mean restrictive eating — it's about understanding sensible serving amounts that fit your health goals. Combined with increased physical activity and, for some people, prescription weight loss medication, portion awareness can help you lose weight at a healthy rate. The NHS recommends aiming for 0.5 to 1 kg per week of weight loss, which typically requires a calorie deficit of around 500 kcal daily. Understanding your personal calorie needs and how portions fit into that target is key to success.
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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.
Portion Control Strategies and Prescription Weight Management Options
Effective portion control techniques include using smaller plates, filling half your plate with vegetables, measuring carbohydrates and proteins carefully, and eating slowly to allow fullness signals to register. The NHS suggests these practical approaches work best alongside consistent habits rather than strict dieting.
For adults struggling with portion control despite these strategies, prescription weight loss medications are available through the UK health system. Three main options are licensed for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 injection administered once weekly, which may help reduce appetite and support feeling fuller after smaller portions
- Wegovy (semaglutide) — a GLP-1 injection given once weekly, which works similarly to help regulate hunger signals
- Saxenda (liraglutide) — a daily GLP-1 injection option for weight management
In clinical trials, these medications supported average weight losses of 15–21% of body weight when combined with reduced-calorie diet and increased physical activity. However, individual results vary significantly. All prescription weight loss medications require clinical assessment to determine suitability and are available through NHS specialist weight management services or private prescribing following an online clinical consultation.
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.
Checking Your Eligibility and Next Steps
In the UK, you may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, as these groups face higher health risks at lower weights.
To explore whether prescription weight management is right for you, start by speaking with your GP, who can refer you to a specialist tier 3 weight management service in your area. Alternatively, you can access private prescribing through GPhC-registered online services following an online clinical assessment. Use our free BMI calculator above to check your current BMI and understand where you fall on NHS guidelines. Our GLP-1 weight loss calculator can help you estimate potential weight loss projections if prescription medication is appropriate for your situation.
- 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.
What is an ideal portion size for weight loss?
Portion sizes depend on your individual calorie target, but general guidance includes: a palm-sized amount of protein per meal, a fist-sized portion of carbohydrates, two handfuls of vegetables, and one thumb-sized portion of fat. Using smaller plates naturally reduces portions without feeling restrictive.
Can portion control alone lead to weight loss?
Yes, portion control can support weight loss if it creates a calorie deficit. However, for some people, particularly those with strong hunger signals or medical conditions affecting appetite, prescription weight loss medication alongside portion control may be more effective and sustainable.
How does prescription weight loss medication help with portions?
Medications like Mounjaro and Wegovy work by reducing appetite and helping you feel fuller after smaller meals. This makes portion control easier because your body naturally signals satisfaction sooner, supporting the calorie deficit needed for weight loss without willpower alone.
What's the difference between NHS and private weight loss medication in the UK?
NHS medication is accessed through specialist tier 3 services, usually following a GP referral, with waiting lists varying by region. Private prescribing is available through online assessments with UK-licensed prescribers and GPhC-registered pharmacies, offering quicker access without referral, though you pay privately.
How quickly can I expect to lose weight with portion control and medication?
The NHS recommends 0.5 to 1 kg per week as a safe, sustainable rate. In clinical trials, prescription medications combined with reduced-calorie diet supported average losses of 15–21% of body weight over several months, but individual results vary significantly depending on adherence and personal factors.
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.