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
Body Composition Chart — What Your Numbers Mean
A body composition chart shows the breakdown of your body weight into muscle, fat, bone, and water — giving you a clearer picture of your health than weight alone. Whilst BMI is a useful screening tool, understanding your body composition helps you see the difference between muscle and fat, which BMI cannot distinguish. Using NHS guidance and evidence-based ranges, this health guide explains body composition categories and how they relate to your overall wellbeing in a UK health context.
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.
Understanding Body Composition Ranges
Body composition is typically measured as body fat percentage, which represents the proportion of your total weight that is fat tissue. The NHS recognises body composition assessment as a valuable addition to BMI screening, particularly for athletes and older adults where BMI may be misleading.
- Women's healthy body fat range: 21–31% (fitness range 14–20%, essential fat 10–13%)
- Men's healthy body fat range: 18–24% (fitness range 6–13%, essential fat 2–5%)
- Obese category: Women 32%+, Men 25%+
These ranges align with clinical evidence and NHS healthy weight guidance. Calculate your BMI using our free BMI calculator above to get your starting point, then track changes in body composition alongside weight loss for a more complete picture of your health progress.
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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.
Why Body Composition Matters More Than Weight Alone
Two people with the same weight can have very different body compositions — one may be muscular whilst the other carries more fat. This is why waist measurement and body composition are important alongside BMI. The NHS recommends monitoring waist circumference as an additional health indicator: men should aim for under 94cm (37 inches), women under 80cm (31.5 inches).
If you're tracking weight loss, use our free weight converter and progress tracker to monitor both weight and measurements over time. Even if the scales don't change, improvements in body composition — gaining muscle whilst losing fat — are a genuine health win and often reflect positive lifestyle changes more accurately than weight alone.
- 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 the difference between BMI and body composition?
BMI is a height-to-weight ratio that's easy to calculate but cannot distinguish between muscle and fat. Body composition specifically measures body fat percentage, giving a more detailed picture of your health. Athletes may have high BMI but low body fat, making body composition assessment more accurate for them.
How is body fat percentage measured?
Methods include DEXA scans (most accurate), bioelectrical impedance (scales), skinfold measurements (calipers), and waist-to-height ratio. Home scales can estimate body fat but aren't clinical-grade. Your GP can refer you for more accurate assessment if needed for health monitoring.
Can I improve body composition without losing weight?
Yes. Strength training builds muscle whilst cardio and dietary changes reduce fat. You may stay the same weight but improve your body composition — losing fat whilst gaining muscle. This is why tracking measurements alongside weight matters more than the scales alone.
What waist measurement is healthy according to NHS guidance?
For UK adults, the NHS recommends: men under 94cm (37in) is healthy, over 102cm (40in) is high risk; women under 80cm (31.5in) is healthy, over 88cm (34.5in) is high risk. Waist measurement is an important health marker alongside BMI and body fat percentage.
Should I focus on body composition or BMI?
Both are useful. BMI is a quick screening tool, but body composition and waist measurement give a more complete health picture. The NHS recommends using all three measures together. Use our free BMI calculator and weight converter to establish your baseline, then monitor changes in all three as part of your health journey.
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.