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
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How to Determine Your Body Fat Percentage
Body fat percentage measures the proportion of fat in your body compared to lean mass (muscle, bone, organs). Unlike BMI, which only uses height and weight, body fat percentage gives a clearer picture of your actual body composition and health risk. There are several ways to determine it—from clinical methods to home estimates—each with different accuracy levels. Understanding your body fat percentage, alongside your BMI, helps you see the complete fitness and health picture.
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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 Determine Body Fat Percentage
Several methods exist to measure or estimate body fat percentage, ranging from highly accurate clinical techniques to practical home options:
- DEXA scan (Gold standard) — Uses low-dose X-rays to measure bone density and body composition. Most accurate but expensive and requires specialist access. Often used in research.
- Hydrostatic weighing — Measures body density by weighing you in water. Very accurate but requires specialist facilities and training.
- Bioelectrical impedance analysis (BIA) — Sends a harmless electrical current through your body to estimate fat percentage. Available via scales, handheld devices, or clinical settings. Accuracy varies (±3–5%). Affordable and convenient.
- Skin calipers (Skinfold measurement) — Technician measures fat thickness at specific body sites. Requires trained assessment but is relatively affordable and portable. Accuracy depends on technician skill.
- BODPOD (Air displacement) — Uses air displacement to measure body volume. Accurate and available at some fitness centres, but less common in the UK.
For most people, BIA scales or fitness tracker estimates provide a practical starting point, though they are less precise than clinical methods.
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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.
Healthy Body Fat Ranges & Why BMI Isn't Enough
The NHS focuses on BMI as a screening tool, but body fat percentage provides crucial additional context. Someone with high muscle mass (like an athlete) may have a high BMI yet low body fat percentage and excellent health. Conversely, someone with a normal BMI may have unhealthily high visceral fat (fat stored around organs), which increases disease risk even at a healthy weight.
NHS healthy body fat ranges (approximate): Women 21–24% (fitness), 25–31% (acceptable). Men 14–17% (fitness), 18–24% (acceptable). Body fat above 32% (women) or 25% (men) is typically classified as obese.
Use our free BMI calculator above to check your BMI alongside body fat assessment for a complete health picture. Your GP can discuss what your specific measurements mean for your individual 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 uses height and weight only and cannot distinguish muscle from fat. Body fat percentage measures actual fat mass versus lean mass. Two people with identical BMI and weight can have very different body compositions and health risks. Body fat percentage is more specific but harder to measure accurately at home.
Can I accurately measure body fat percentage myself?
Home bioelectrical impedance scales (smart scales) provide reasonable estimates but are typically accurate to within ±3–5%. Accuracy depends on hydration, time of day, and device quality. For clinical accuracy, DEXA scans or hydrostatic weighing are better. Home estimates are useful for tracking trends over time rather than absolute values.
Is 25% body fat healthy for a woman?
Yes. According to fitness and health standards, 21–24% is the fitness range and 25–31% is the acceptable/average range for women. Both are considered healthy. Above 32% is typically classified as obese. However, individual health depends on many factors—your GP can advise what's appropriate for your personal health context.
What's visceral fat and why does it matter?
Visceral fat is stored around internal organs (liver, pancreas, heart). It's metabolically active and increases risk of type 2 diabetes, heart disease, and inflammation—even in people with normal weight or BMI. Waist circumference (over 80cm for women, 94cm for men = increased risk) is a practical proxy for visceral fat risk. Reducing overall body fat helps reduce visceral fat.
Should I focus on body fat percentage instead of weight loss?
No—track both. Weight loss often combines fat loss and muscle loss. If you're exercising, your weight might stay the same while body fat decreases and lean mass increases (a positive change). Body fat percentage shows whether weight changes reflect fat loss or muscle gain. Progress tracker tools help monitor both metrics over time.
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.