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 to Figure Out Percentage of Body Fat
Body fat percentage is a more detailed measure of health and fitness than weight alone, as it distinguishes between muscle and fat in your body. Unlike BMI, which uses only height and weight, body fat percentage gives you insight into your actual lean body mass and overall body composition. This guide explains how to use our body fat calculator on this page and what your results mean for your health according to UK health guidelines.
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 to Interpret Your Body Fat Calculator Results
Our body fat calculator uses measurements of your height, weight, age, and gender to estimate your body fat percentage. Once you have your result, compare it to the healthy body fat ranges for your gender:
- Women: Essential fat 10–13%, Athletic 14–20%, Fitness 21–24%, Acceptable 25–31%, Obese 32%+
- Men: Essential fat 2–5%, Athletic 6–13%, Fitness 14–17%, Acceptable 18–24%, Obese 25%+
These ranges show that healthy body composition varies by gender. A body fat percentage of 20–25% for women or 15–20% for men is generally considered fit and healthy. Results in the "acceptable" range indicate good health, though fitness ranges suggest better metabolic health. Your GP can discuss what your individual results mean in context of your overall health profile.
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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 Guidance and Next Steps
Body fat percentage and BMI measure different things. BMI is a simple screening tool based only on height and weight—it cannot distinguish between muscle and fat. This means a muscular athlete might have a high BMI but healthy body fat percentage. Conversely, someone with a normal BMI might have high visceral fat (dangerous fat around organs). Body composition provides the fuller picture. For general population screening, BMI remains useful, but body fat percentage is more accurate for understanding whether excess weight is muscle or fat. Both metrics together give you the most complete view of your metabolic 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 the difference between body fat percentage and BMI?
BMI uses only height and weight to estimate health risk. Body fat percentage distinguishes between muscle and fat mass, making it more accurate for assessing true body composition. BMI can misclassify muscular individuals as overweight, while body fat percentage reveals the actual proportion of fat tissue.
Is there a healthy body fat percentage for UK adults?
Yes. For women, 21–31% is generally considered acceptable and healthy; for men, 14–24%. The NHS and fitness professionals use these ranges as reference points. Factors like age, genetics, and activity level affect individual targets, so discuss your personal healthy range with your GP.
How accurate is a body fat calculator?
Body fat calculators estimate based on measurements and formulas—they are typically within 3–5% accuracy compared to clinical methods like DEXA scans. For tracking progress over time, they are reliable as long as you use the same calculator consistently. For precise clinical assessment, your GP can arrange more advanced measurement.
Can I improve my body fat percentage without losing weight?
Yes. Regular resistance training and strength exercises increase muscle mass while potentially reducing fat mass, sometimes with little change in overall weight. This improves body composition even if the scale stays the same. A higher proportion of muscle increases metabolic rate and improves health markers like blood pressure and glucose control.
Why does body fat percentage matter more than the number on the scales?
Two people at the same weight can have very different health profiles depending on body composition. High lean body mass (muscle) supports metabolism, bone density, and strength. Excess body fat—especially visceral fat around organs—increases inflammation and disease risk. Body fat percentage reveals what matters most: the quality of your body composition, not just the total 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.