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 Percentage and Why Does It Matter?
Body fat percentage measures the proportion of fat in your body compared to muscle, bone, and other lean tissue. Unlike BMI, which only considers weight and height, body composition analysis gives you a much clearer picture of your health. A healthy body fat percentage varies by age and gender, and understanding yours helps you set realistic fitness goals and track meaningful progress over time.
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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.
How to Interpret Your Body Fat Results
When you use our free body fat calculator on this page, your result falls into one of several health categories. For women: essential fat is 10–13%, athletic is 14–20%, fitness is 21–24%, acceptable is 25–31%, and obese is 32% or above. For men: essential fat is 2–5%, athletic is 6–13%, fitness is 14–17%, acceptable is 18–24%, and obese is 25% or above. These ranges are based on age-adjusted UK and international health standards.
Remember that these are reference ranges—your ideal body fat percentage also depends on your age, fitness level, and individual health goals. A professional body composition assessment can give you a more personalised picture. If you're unsure where you fall or have health concerns, chat with your GP for guidance tailored to your circumstances.
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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.
Body Fat vs BMI — Which Metric Should You Use?
Body fat percentage tells you the actual composition of your body—how much is fat versus lean muscle. BMI is a screening tool based purely on height and weight. You can have a "healthy" BMI but high body fat (poor muscle tone), or a high BMI with low body fat (if you're very muscular). Use our free BMI calculator alongside this tool to get a complete picture.
For most people, tracking both metrics together gives the clearest health insight. Body fat percentage is especially useful if you're exercising regularly, as muscle weighs more than fat—so the scales might not move even though your body composition is improving. Body composition also reveals visceral fat (dangerous fat around organs), which BMI alone cannot detect.
- 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 my age?
Healthy ranges vary by gender and age. Generally, women aged 20–40 with 21–24% body fat are in the "fitness" category, while men the same age with 14–17% are considered fit. These ranges increase slightly with age due to natural metabolic changes. Our calculator provides age-specific guidance—use it to see where you fall, then discuss results with your GP if you have concerns.
Is body fat percentage more accurate than BMI?
Both metrics serve different purposes. Body fat percentage directly measures fat versus lean mass, making it superior for tracking body composition. However, BMI is a quick screening tool and correlates well with health risks at a population level. For the most complete picture, use our free BMI calculator and body fat calculator together to understand your overall health status.
Can I have a high BMI but low body fat?
Yes, absolutely. Athletes and people with significant muscle mass often have high BMI but low body fat percentage, because muscle is denser than fat. This is why body composition analysis is so valuable—it reveals what your weight actually consists of. If you're very active, body fat percentage is often a better progress indicator than weight alone.
How does visceral fat differ from body fat percentage?
Body fat percentage measures total fat (subcutaneous fat under the skin plus visceral fat around organs). Visceral fat is particularly harmful to heart and metabolic health, even in people with "normal" overall body fat. Unfortunately, standard body fat calculators cannot isolate visceral fat—you'd need imaging like a DEXA scan or CT scan for precise measurement. Maintaining a healthy waist circumference (under 80cm for women, 94cm for men) helps control visceral fat.
Should I use body fat percentage or weight to track weight loss progress?
Ideally, track both. Weight tells you overall change; body fat percentage and our free progress tracker show whether you're losing fat or muscle. During weight loss, aim for steady progress (0.5–1kg per week) while monitoring body composition. If body fat drops while weight stays similar, you're building muscle—which is excellent progress even if scales don't move.
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.