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 Is Body Fat Percentile?
Body fat percentile measures how your body composition compares to others of the same age and sex. It shows what percentage of your total weight is fat versus lean body mass (muscle, bone, water). Unlike BMI, which only uses height and weight, body fat percentile provides a more complete picture of your overall health and fitness. The NHS recognises that body composition is an important complement to BMI screening, especially for active individuals and older adults.
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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.
Body Fat Percentile Ranges by Sex and Category
Body fat percentile is typically categorised into five ranges. For women: essential fat (10–13%), athletic (14–20%), fitness (21–24%), acceptable (25–31%), and obese (32%+). For men: essential fat (2–5%), athletic (6–13%), fitness (14–17%), acceptable (18–24%), and obese (25%+). These ranges reflect healthy fat percentage for body function—some fat is essential for hormone production, insulation, and organ protection. Use our free BMI calculator alongside body composition assessment to get a fuller picture of your health status. Age also matters; healthy ranges shift slightly with age, as muscle mass naturally declines and fat percentage typically increases with years.
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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.
How Body Fat Percentile Differs From BMI
Body composition and BMI measure different things. A person with high muscle mass might have a high BMI but low fat percentage—think athletes or very fit individuals. Conversely, someone with a normal BMI could have unhealthy visceral fat distribution. Body fat vs BMI: BMI is quick and simple, but body composition gives you depth. The NHS uses BMI as a screening tool precisely because it's accessible; however, GPs increasingly recommend waist circumference and body composition measurement for those with concerning health markers. If you're worried about your weight or composition, our weight converter helps you understand your current weight in UK measurements (stone and pounds), then discuss both metrics with your GP.
- 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 a healthy body fat percentage for an average UK adult?
For women, 18–31% is generally considered healthy depending on age and fitness level; for men, 10–24%. However, healthy ranges vary by age—a 50-year-old woman's healthy range differs from a 25-year-old's. Your GP can advise on what's healthy specifically for you.
How is body fat percentage measured?
Methods include DEXA scans (gold standard, used in clinical settings), bioelectrical impedance scales (common but less accurate), skinfold calipers, or underwater weighing. Many NHS weight management services use simple measurements like waist circumference as a practical alternative.
Can I have a normal BMI but high body fat percentage?
Yes—this is called "normal weight obesity." Someone might have a healthy BMI but excess visceral fat, particularly around organs. This is why the NHS recommends checking waist circumference alongside BMI, especially for older adults.
Does body fat percentage matter more than BMI?
Neither is perfect alone. Body composition matters for health, but BMI is useful for population screening. The best approach uses both: calculate your BMI with our free BMI calculator, assess your waist measurement, and discuss your overall health picture with your GP.
How does age affect healthy body fat percentages?
As we age, muscle naturally declines and fat percentage increases. A healthy range for a 60-year-old is higher than for a 30-year-old. The NHS recognises this when assessing weight-related health risks. Your GP can advise on age-appropriate healthy ranges for you.
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.