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
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Understanding Body Fat and Its Role in UK Health
Body fat is an essential part of your body composition, but the amount you carry affects your health outcomes. In the UK, the NHS recognises that body fat percentage is a more accurate health indicator than weight alone, as it distinguishes between muscle mass and excess fat. This guide explains what body fat is, healthy ranges for UK adults, and how it relates to your overall wellbeing. Whether you're tracking weight management or assessing your fitness level, understanding your body composition is a key part of maintaining good health.
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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.
What Is Body Fat and Why Does It Matter?
Body fat is the percentage of your total body weight that consists of fat tissue. Unlike your overall weight, body fat percentage tells you how much of your mass is actual fat rather than muscle, bone, or water. This is crucial because two people of the same height and weight can have very different health risks depending on their body fat distribution.
The NHS recognises body fat percentage as part of a comprehensive health assessment alongside BMI. While BMI is useful as a screening tool, it doesn't distinguish between muscle and fat — a bodybuilder and someone with excess weight might have the same BMI but very different body fat levels.
- Essential fat: 10–13% for women, 2–5% for men — necessary for organ protection and hormone regulation
- Athletic range: 14–20% for women, 6–13% for men — associated with good fitness levels
- Healthy range: 21–31% for women, 14–24% for men — considered acceptable for most adults
Body fat also matters because excess fat stored around the abdomen (visceral fat) poses greater health risks than fat stored elsewhere, even at the same overall percentage.
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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.
UK Health Tools and Getting Started
The best way to understand your body composition is to use multiple measurement methods. Our free BMI calculator gives you a baseline health screening, whilst our weight converter helps you track your weight across kg, stone, and pounds — the measurements most UK adults use daily.
If you're working on weight management, our GLP-1 weight loss calculator can help you project potential outcomes if you're considering prescription weight loss support. For ongoing tracking, use our free progress tracker to log changes over time — body recomposition (losing fat whilst gaining muscle) means the scales might not move, but your measurements and how you feel will improve.
Your GP can also refer you for professional body composition analysis using DEXA scans or other methods on the NHS. Start by discussing your health goals with your practice — they can provide personalised guidance based on your individual circumstances.
- 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 body fat percentage and BMI?
BMI measures total weight relative to height but doesn't distinguish muscle from fat. Body fat percentage specifically measures the proportion of fat tissue, making it a more detailed health indicator. Both metrics together give a fuller picture of your body composition and health risk.
What body fat percentage should I aim for as a UK adult?
For women, a healthy range is typically 21–31%; for men, 14–24%. However, individual goals vary based on age, fitness level, and health conditions. Your GP can advise on what's appropriate for you. Our BMI calculator can also help assess your baseline health status.
How can I measure my body fat percentage at home?
Home methods include skinfold callipers, scales with bioelectrical impedance, or waist-to-hip ratios. These are less accurate than clinical methods but useful for tracking trends over time. The most accurate NHS method is a DEXA scan, available through your GP if medically indicated.
Does body fat percentage matter more than weight for health?
Both matter, but body fat distribution is often more important than total weight. Visceral fat (around organs) poses greater health risks than subcutaneous fat. Use our weight converter and BMI calculator together to get a complete picture of your weight and health status.
Can I lose fat without losing weight?
Yes — this is called body recomposition. If you're building muscle whilst losing fat, your weight may stay similar but your body composition improves significantly. This is why tracking measurements, energy levels, and how clothes fit matters as much as scale weight.
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.