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 You Figure Out Body Fat?
Body fat percentage is a more detailed measure of your health than weight alone. While BMI tells you your overall weight category, body fat percentage reveals how much of your body is actually fat versus muscle, bone, and water. There are several methods to measure it, from simple home calculations to clinical assessments. Understanding your body fat percentage helps you track whether weight changes reflect fat loss or muscle gain—something your bathroom scales can't tell you.
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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 Body Fat Percentage
Several approaches exist to calculate your body fat percentage, each with different accuracy levels:
- Skinfold callipers: A healthcare professional pinches skin at specific sites (triceps, biceps, subscapular, suprailiac) and uses equations to estimate body fat. Accuracy depends on the measurer's skill.
- DEXA scan: The gold-standard clinical method. Uses dual-energy X-ray absorptiometry to measure lean body mass and fat distribution. Available at private clinics and some NHS centres.
- Bioelectrical impedance analysis (BIA): A small electrical current passes through your body to estimate fat versus muscle. Less accurate than DEXA but available in gyms and home scales.
- Waist circumference: Simple measure of visceral fat—the dangerous fat around organs. Men over 94cm (37 inches) and women over 80cm (31.5 inches) face increased health risks, regardless of BMI.
- Online calculators: Use your age, gender, height, and weight to estimate body fat. Less accurate than clinical methods but useful for tracking trends over time.
Your GP can discuss which method suits your health goals and refer you to appropriate services if needed.
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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
Body fat versus BMI tells a very different story. Two people with identical BMI can have completely different body composition: one might be muscular, the other carrying excess fat. This is why athletes often have a "high" BMI despite low body fat. Measuring your body fat percentage reveals whether you're losing fat (positive) or losing muscle (concerning). Use our free BMI calculator above to check your BMI, then consider body fat measurement for a fuller picture. NHS guidance emphasises that waist measurement alongside BMI provides better cardiovascular risk assessment than BMI alone. Sustainable weight loss should preserve muscle while reducing fat—something only body composition tracking can confirm.
- 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 UK adults?
For women, 21–31% is typically considered healthy (athletic: 14–20%, fitness: 21–24%). For men, 18–24% is healthy (athletic: 6–13%, fitness: 14–17%). However, healthy range depends on age, fitness level, and individual health factors. Your GP can advise what's appropriate for you.
Can I measure body fat at home?
Yes, home methods exist but vary in accuracy. Consumer bioelectrical impedance scales are convenient but less reliable than clinical methods. Skinfold callipers require practice to use correctly. For the most accurate result, ask your GP about DEXA scans or professional body composition analysis at private clinics.
Is body fat percentage more important than weight?
Both matter for different reasons. Weight tells you if you're gaining or losing mass overall. Body fat percentage tells you whether that change is fat loss or muscle loss. NHS guidance recommends looking at both alongside waist circumference and overall health markers, not just one measure alone.
Why is waist circumference important?
Waist measurement identifies visceral fat—dangerous fat around organs linked to type 2 diabetes and heart disease—that BMI alone can't detect. Men over 94cm and women over 80cm face increased health risks even at a normal BMI. It's a quick, free screening tool your GP can measure.
How often should I measure body fat?
Monthly measurements are useful for tracking trends without fixating on day-to-day fluctuations. Water retention, digestion, and hormones cause daily variations that don't reflect real fat loss. A progress tracker can help log measurements over time and spot genuine changes in your body composition.
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.