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 a Body Fat Calculator and Why Does It Matter?
A body fat calculator estimates what percentage of your total weight is fat versus muscle, bone, and organs. Unlike BMI, which only measures weight relative to height, body fat percentage gives you a clearer picture of your actual body composition. Knowing your body fat percentage is important because two people at the same weight and height can have very different health profiles depending on their muscle mass and fat distribution. This is especially useful if you're tracking fitness progress or assessing your overall health risk. Your GP or a healthcare professional can help interpret what your body fat percentage means for your individual circumstances.
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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.
Body Fat Percentage Ranges and Healthy Categories
Body fat percentage is measured as the proportion of your total body weight that is fat tissue. The NHS recognises that healthy ranges vary significantly by age and sex. For women, a healthy body fat range is typically 21–31%, while for men it's 10–20%. However, essential fat — the minimum amount your body needs to function — is 10–13% for women and 2–5% for men.
- Athletic body fat: Women 14–20%, men 6–13% — typically associated with regular exercise
- Fitness range: Women 21–24%, men 14–17% — sustainable with consistent activity
- Acceptable range: Women 25–31%, men 18–24% — normal for most healthy adults
- Above healthy levels: Women 32%+, men 25%+ — may indicate increased health risks
Remember that body composition matters more than the number on the scales. Two people weighing 70kg can have completely different body fat percentages depending on their muscle mass. This is why our free BMI calculator should be used alongside body fat assessment for a complete health picture.
Clinically BackedWeight Loss
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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 Differs from BMI and Why Both Matter
BMI and body fat vs BMI comparisons reveal important differences. BMI is a screening tool based only on height and weight — it cannot distinguish between muscle and fat. An athlete with significant lean body mass might have a "high" BMI despite low visceral fat and excellent health. Conversely, someone with a "normal" BMI might carry excess fat if they have low muscle mass.
For this reason, the best approach is to use both measures. Calculate your BMI using our free weight converter and BMI calculator to get your BMI, then consider your body fat percentage for context. Waist circumference is also valuable — women with waist over 80cm and men over 94cm face increased health risks, regardless of BMI or body fat alone. Your GP can advise on what combination of these measurements means for your personal 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's the difference between body fat percentage and BMI?
BMI measures weight relative to height but cannot distinguish muscle from fat. Body fat percentage shows the actual proportion of fat tissue. Two people with identical BMI can have very different body compositions — one muscular, one with excess fat. For a complete picture, assess both measures using tools like our free BMI calculator alongside body fat assessment.
What is a healthy body fat percentage for women and men?
For women, a healthy range is typically 21–31%; for men, 10–20%. Essential fat minimums are 10–13% for women and 2–5% for men. These ranges account for normal variation and are based on UK health guidelines. However, individual health depends on many factors, so discuss your personal targets with your GP.
Why is body composition important if my BMI is healthy?
BMI alone misses the picture. High muscle mass can create a high BMI despite low body fat and excellent health. Conversely, low muscle mass with high fat can produce a "normal" BMI with actual health risks. Body composition reveals whether your weight comes from muscle or fat — crucial information for understanding cardiovascular and metabolic health.
How is body fat percentage measured?
Methods include bioelectrical impedance analysis (scales), DEXA scans, callipers, and hydrostatic weighing. Home scales are convenient but less accurate than clinical methods. For the most reliable assessment, ask your GP or a registered fitness professional. Our free progress tracker can help you monitor changes over time regardless of measurement method.
Does visceral fat matter differently than other body fat?
Yes. Visceral fat surrounds organs and is metabolically active, increasing inflammation and disease risk. It's more dangerous than subcutaneous fat under the skin. Unfortunately, standard body fat tests don't measure visceral fat separately. Waist circumference is a practical proxy — women over 80cm and men over 94cm carry increased risk. Talk to your GP about your individual risk profile.
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.