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
How Portion Size Affects Weight Loss
Portion size is one of the most effective levers for achieving sustainable weight loss. Reducing how much you eat at each meal creates the calorie deficit needed to lose weight at the NHS-recommended rate of 0.5–1 kg per week. Unlike restrictive diets, portion control focuses on eating normally but in smaller amounts — making it easier to stick with long-term. Combined with increased physical activity, portion management is the foundation of weight management in the UK.
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.
Why Portion Size Matters for Weight Loss
Portion size directly controls calorie intake. A calorie deficit of roughly 500 kcal per day results in losing approximately 0.5 kg weekly — the safe, sustainable rate recommended by the NHS. If your portions are too large, even healthy foods contribute excess calories that prevent weight loss.
Research shows that people often underestimate how much they eat. A standard restaurant meal can contain 1,000+ kcal in a single sitting — equivalent to half a day's calorie allowance for many adults. Portion control helps recalibrate your eating patterns.
Key benefits of smaller portions:
- Creates the calorie deficit needed for weight loss
- Helps regulate blood sugar and energy levels
- Reduces overeating and food waste
- Works with any diet approach — no foods are "banned"
- Supports long-term habit change rather than temporary restriction
Use our free BMI calculator above to check your current weight category, then track progress as you adjust portions.
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.
Practical Portion Control Strategies
Simple techniques to reduce portions without feeling deprived: Use smaller plates (9-inch instead of 11-inch) — this creates a visual illusion of fullness. Fill half your plate with vegetables, one quarter with protein, and one quarter with carbohydrates. Eat slowly and pause halfway through meals — it takes 20 minutes for your brain to register fullness.
Measure your food initially using scales or cup measures to understand actual portion sizes. Keep high-calorie foods like oils and spreads to measured amounts. Drink water before meals to reduce overall intake. When eating out, ask for half portions or share a main course.
Track your weight loss with our free progress tracker to see how portion adjustments impact your results over time.
- 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 smaller should my portions be for weight loss?
To lose approximately 0.5 kg per week, you need a calorie deficit of around 500 kcal daily. For most adults, this means reducing portion sizes by roughly 20–30%. Start by reducing portions slightly, then adjust based on your progress. Our free BMI calculator helps you understand your baseline.
Can I lose weight just by reducing portions without dieting?
Yes — portion control alone can create the calorie deficit needed for weight loss. You don't need to cut out specific foods, just eat smaller amounts. This approach is often more sustainable than restrictive diets and aligns with NHS weight management guidance.
Does portion control work better than weight loss medication?
Portion control is the foundation of all sustainable weight loss. Prescription weight loss injections like Mounjaro and Wegovy work by reducing appetite and food cravings, making portion control easier to maintain. They're most effective when combined with smaller portions and lifestyle changes.
How do I know what a healthy portion size is?
The NHS recommends: fill half your plate with vegetables, one quarter with protein (chicken, fish, beans), and one quarter with carbohydrates (rice, bread, pasta). Use the weight converter on this page to understand how portion sizes translate between different measurements.
Will smaller portions cause me to feel hungry all the time?
Not if you choose the right foods. Protein and fibre-rich foods (vegetables, whole grains, legumes) keep you fuller longer than processed foods. Eat slowly, drink water, and give your body 2–3 weeks to adapt to new portion sizes — hunger typically decreases as your stomach adjusts.
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.