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 Do I Determine Body Fat Percentage
Body fat percentage is a more accurate measure of health than weight alone, as it shows how much of your body is fat versus muscle and bone. There are several methods to measure body fat, ranging from simple calculations to professional assessments. Understanding your body composition helps you set realistic health goals and track meaningful changes in your body, regardless of what the scales say.
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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.
Methods to Measure Your Body Fat
The most practical methods to determine your body fat percentage include:
- Bioelectrical impedance analysis (BIA) — Sends a harmless electrical signal through your body to estimate fat mass. Available in many gyms and home scales. Accuracy varies (±3–5%).
- Skinfold calipers — A trained professional measures thickness at specific body sites (triceps, biceps, chest, abdomen) and calculates fat percentage. Requires skill but is low-cost and portable.
- DEXA scan — Gold standard measurement using low-dose X-rays. Provides precise lean body mass, fat mass, and bone density. Usually available through private health clinics or research centres in the UK.
- Waist circumference — Simple tape measurement at your natural waist. Indicates visceral fat (dangerous fat around organs). Men: over 94cm = increased health risk; over 102cm = high risk. Women: over 80cm = increased risk; over 88cm = high risk.
- Waist-to-height ratio — Waist circumference divided by height. Healthy ratio is below 0.5 for all adults. Easy to calculate and surprisingly accurate for predicting cardiovascular risk.
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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 Fat Matters More Than BMI Alone
BMI does not distinguish between muscle and fat — a muscular athlete may have a high BMI but low body fat percentage. This is why body composition is crucial. Two people at the same weight can have very different health profiles depending on how much is muscle versus fat.
Visceral fat (deep abdominal fat around organs) is particularly harmful to health, even if overall body fat percentage is normal. This is why measuring waist circumference gives valuable health information that weight alone cannot. Track your body composition using our free progress tracker to see meaningful changes beyond the scales, and use our BMI calculator alongside body fat assessment for a complete picture of your health.
- 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 a healthy body fat percentage for adults in the UK?
Healthy ranges vary by age and sex. For women: athletic 14–20%, fitness 21–24%, acceptable 25–31%. For men: athletic 6–13%, fitness 14–17%, acceptable 18–24%. These are guidelines — your GP can advise what's appropriate for you personally.
Is body fat percentage more accurate than BMI?
Both are useful but measure different things. Body fat percentage shows composition (muscle vs fat). BMI is a quick screening tool but doesn't account for muscle. Together they give a more complete picture of health than either alone.
Can I measure my own body fat at home?
Yes, several methods work at home: smart scales (BIA), waist circumference with a tape measure, or waist-to-height ratio calculations. For most accuracy, ask your GP to refer you for professional measurement like DEXA or skinfold calipers.
What does visceral fat mean and why is it dangerous?
Visceral fat is stored deep in the abdomen around organs. Even normal-weight people can have too much visceral fat, which increases risk of type 2 diabetes, heart disease, and fatty liver disease. Waist circumference is a good indicator of visceral fat levels.
How often should I check my body composition?
Monthly checks are reasonable if tracking progress. Avoid weekly measurements — body composition changes slowly. More frequent checks can be demotivating if you're also building muscle, as muscle weighs more than fat. Consistency matters more than frequency.
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.