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 Work Out Your Body Fat Percentage
Body fat percentage measures the proportion of fat in your total body weight, expressed as a percentage. Unlike BMI, which only considers height and weight, body fat percentage provides a more detailed picture of your body composition by distinguishing between fat mass and lean body mass (muscle, bone, water). This metric is particularly useful because two people with the same BMI can have vastly different body compositions. Understanding your body fat percentage helps you track meaningful changes in your health, even when the scales don't move. Use our free body fat calculator above to estimate yours and see how it compares to healthy reference ranges for your age and gender.
10,000+ calculations today ยท NHS-aligned thresholds ยท 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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Understanding Your Body Fat Calculator Results
The calculator above uses standard equations (Katch-McArdle and Deurenberg formulas) to estimate your body fat percentage based on your measurements. These are scientifically validated prediction methods widely used in UK fitness and health assessment. Your result falls into one of several categories based on NHS and fitness industry guidelines.
Reference ranges by gender:
- Women: Essential fat 10โ13%, Athletic 14โ20%, Fitness 21โ24%, Acceptable 25โ31%, Obese 32%+
- Men: Essential fat 2โ5%, Athletic 6โ13%, Fitness 14โ17%, Acceptable 18โ24%, Obese 25%+
These ranges show that "acceptable" body fat does not mean optimal health โ the fitness and athletic ranges represent better health markers. Keep in mind that essential fat (the minimum needed for organ function and hormone regulation) is higher in women due to reproductive requirements. Your age also matters: slightly higher percentages are normal and healthy as you get older.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
Body Fat Percentage vs BMI โ Which Matters More?
BMI is useful for population-level screening, but body fat percentage provides a more complete picture of your health. An athlete with significant muscle mass may have a high BMI yet low body fat โ using BMI alone would incorrectly suggest they are overweight. Conversely, someone with a healthy BMI might have high body fat and low muscle mass, which carries its own health risks.
When each metric matters: Use our free BMI calculator alongside this body fat calculator to get both perspectives. BMI is a quick screening tool; body fat percentage is more specific to composition. Together, they reveal more about your actual health than either metric alone. Visceral fat (fat stored around organs) is particularly important to monitor โ even lean-looking individuals can have excessive visceral fat, which increases disease risk.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 height-to-weight ratio only and cannot distinguish muscle from fat. Body fat percentage directly measures the proportion of fat in your body. Two people with identical BMI can have very different body compositions. This is why body fat percentage is often considered a more accurate health indicator than BMI alone.
Are these calculator results accurate?
The calculator uses validated prediction formulas (Katch-McArdle and Deurenberg) that estimate body fat from measurements. Results are typically accurate to within ยฑ3โ5% of lab-measured values. For absolute precision, DEXA scanning or hydrostatic weighing at a clinic is needed, but these estimates are reliable for tracking changes over time.
What body fat percentage should I aim for?
This depends on your age, gender, and goals. For general health, the "acceptable" range (18โ24% for men, 25โ31% for women) is healthy. Athletic ranges (6โ13% for men, 14โ20% for women) represent fitness-focused targets. Discuss your personal health goals with your GP to set realistic targets based on your individual circumstances.
Why do I need to know my body fat percentage?
Body fat percentage is a better health marker than weight alone because it shows your body composition. Losing fat whilst gaining muscle can improve your health significantly without major weight changes. Tracking body fat helps assess whether lifestyle changes (diet and exercise) are working, even when scales fluctuate due to water or muscle gain.
How often should I measure my body fat percentage?
Measure every 4โ8 weeks to track meaningful changes. Weekly measurements are unreliable due to natural fluctuations in hydration and hormones. Use our free progress tracker on this site to log your measurements over time, which helps you identify real trends in your body composition rather than day-to-day noise.
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.