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
What Does Weight Loss Really Mean? Comparing to Everyday Objects
Weight loss figures can feel abstract—what does losing 5kg or 20kg actually mean in your daily life? Understanding weight loss in relatable terms helps you set realistic goals and appreciate progress you make. Whether through prescription weight loss medication, dietary changes, or increased physical activity, knowing what your target weight means for your health and wellbeing is essential for sustainable 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.
How Much Weight Loss Makes a Real Difference?
The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results alongside reduced-calorie diet and increased physical activity. Even modest weight loss brings significant health benefits. A 5% reduction in body weight—for example, losing 4kg if you weigh 80kg—can lower blood pressure, improve blood sugar control, and reduce joint strain. Losing 10% of your body weight produces even more noticeable improvements: better sleep quality, increased energy, reduced medication needs for type 2 diabetes or hypertension, and lower cardiovascular risk.
Use our free BMI calculator above to see where you currently sit and what a healthier weight range looks like for your height. For those exploring prescription weight loss options like GLP-1 medications, our weight loss calculator can help estimate potential outcomes at different doses.
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.
Putting Weight Loss in Perspective: Real Objects
To make weight loss tangible, consider this: 1 kg equals roughly a litre of water or a bag of sugar. Losing 5 kg is like removing five bags of sugar from your body. 10 kg is equivalent to a small car tyre or a large household bag of potatoes. 20 kg is about the weight of an average two-year-old child. When prescription weight loss injections like Mounjaro or Wegovy help you lose an average of 15–20% of your body weight, that could mean shedding 12–24 kg for someone weighing 80 kg—genuinely life-changing weight loss. Track your journey using our free progress tracker to see progress week by week.
- 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's considered significant weight loss?
The NHS defines significant weight loss as 5–10% of your body weight, which brings measurable health improvements: lower blood pressure, better blood sugar control, and reduced joint pain. For example, if you weigh 80kg, losing 4–8kg produces real benefits.
How long does it take to lose 5kg safely?
At the NHS-recommended rate of 0.5–1 kg per week, losing 5 kg takes 5–10 weeks. This pace is sustainable and prevents muscle loss. Faster loss is possible with medical support but requires GP oversight.
Can I lose weight using prescription injections like Wegovy?
Wegovy (semaglutide) is a prescription-only GLP-1 injection licensed in the UK for weight management. Clinical trials showed participants lost an average of 15% body weight—though individual results vary. You need a clinical assessment to determine eligibility.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only injections for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but individual results vary significantly.
How do I know if weight loss medication is right for me?
Prescription weight loss treatment is available through NHS specialist services or private prescribers if you have a BMI of 30 or above, or 27+ with weight-related health conditions. Your GP can assess suitability or you can have an online clinical consultation with a licensed prescriber.
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.