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 Fat Calculator UK — What You Need to Know
A body fat calculator helps you understand your body composition by estimating what percentage of your body weight is fat versus muscle, bone, and other tissue. Unlike BMI, which only uses height and weight, body fat percentage and lean body mass provide a more complete picture of your health. This guide explains how body composition assessment works in the UK, healthy body fat ranges for different ages and sexes, and why measuring body fat is valuable alongside BMI screening. Use our free BMI calculator above to check your BMI, then explore body fat as a complementary health measure.
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.
Body Fat Percentage Ranges and Health Categories
Body fat percentage varies by age and sex. The following ranges reflect NHS and fitness industry standards for UK adults:
- 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%+
Essential fat is the minimum needed for basic biological function. An acceptable range for most adults is 18–31% for women and 10–24% for men, depending on age. Unlike BMI, body fat percentage accounts for muscle mass—athletes may have a high BMI but low body fat because muscle is denser than fat. Visceral fat (fat stored around organs) poses particular health risks, even in people with a normal BMI, making body composition assessment valuable for comprehensive health screening.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Body Fat vs BMI — Why Both Measurements Matter
BMI (body mass index) is a simple screening tool using only height and weight, but it cannot distinguish between muscle and fat. Someone with significant muscle mass may have a high BMI yet excellent body composition. Conversely, a person with a normal BMI might carry excess body fat and insufficient muscle.
Body fat percentage fills this gap by showing the actual proportion of fat tissue. Waist-to-height ratio is another useful measure—keeping your waist circumference below 50% of your height is associated with better health outcomes. For comprehensive health assessment, your GP may recommend considering BMI, waist circumference, body fat percentage, and overall fitness together rather than relying on any single metric.
- 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.
How is body fat percentage calculated?
Body fat calculators use several methods: skinfold measurements (calipers), bioelectrical impedance analysis (scales or handheld devices), DEXA scans, or hydrostatic weighing. Online calculators estimate body fat using your age, sex, height, weight, and measurements. None are perfectly accurate at individual level—±3–5% variance is common—but trends over time remain useful for tracking body composition changes.
What's a healthy body fat percentage for UK adults?
For women, 18–31% is generally considered healthy; for men, 10–24%. However, optimal ranges depend on age—healthy ranges increase slightly with age due to natural muscle loss. Your GP can advise what's appropriate for your age and health status. Athletic individuals may aim for lower ranges, while fitness and health are more important than hitting a specific percentage.
Why does body fat matter more than just weight loss?
When you lose weight, ideally you're losing mostly fat while preserving muscle. Muscle is metabolically active and supports strength, mobility, and long-term health. Tracking body fat percentage alongside weight helps ensure your weight loss is coming from fat, not muscle. This is especially important during dieting or when using weight loss medication, where muscle preservation matters.
Can I improve my body composition without changing my weight?
Yes. Building muscle through strength training while maintaining or losing fat can improve body composition without significant weight change—muscle weighs more than fat, so the scale may not move while your body fat decreases. This is why body composition measurement is more informative than weight alone for assessing fitness progress and health improvements.
Should I use a body fat calculator or get a professional assessment?
Online calculators are convenient and free for tracking trends, but they're estimates. For accuracy, a GP, registered dietitian, or fitness professional can arrange skinfold measurements or bioelectrical impedance analysis. For most people, tracking trends over weeks and months with the same calculator method is more useful than a single precise measurement, helping you monitor whether your body composition is improving. ```
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.