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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Body Fat Percentage Calculator — UK Health Information
Body fat percentage (BFP) is a more detailed measure of body composition than BMI alone, as it shows what proportion of your weight is fat tissue versus muscle, bone, and organs. Whilst BMI is useful for general health screening, body fat percentage gives you a clearer picture of whether your weight is healthy for you personally. This guide explains how to calculate and interpret body fat percentage, and how it relates to your overall health alongside other UK health metrics.
10,000+ calculations today · NHS-aligned thresholds · 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/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 Body Fat Percentage Works and Why It Matters
Body fat percentage is calculated as the total weight of fat tissue divided by total body weight, expressed as a percentage. Unlike BMI, which only uses height and weight, body fat percentage accounts for muscle mass — this is crucial because muscle is denser than fat, so two people at the same weight and height can have very different body compositions.
- Essential fat: The minimum fat your body needs for vital functions (2–5% for men, 10–13% for women)
- Healthy ranges: Men 6–24%, women 14–31%, depending on age and fitness level
- Athletic ranges: Men 6–13%, women 14–20%
Measurement methods include DEXA scans (most accurate), skinfold callipers, bioelectrical impedance, and mathematical estimation formulas. For UK health purposes, NHS professionals typically use BMI as a screening tool first, then may assess body composition in specialist weight management services.
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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 Percentage vs BMI — Which Matters More?
BMI is quick and useful for population-level health screening, but it cannot distinguish between muscle and fat. An athlete with significant muscle mass may have a "high" BMI but low body fat percentage — the opposite of health concern. Body fat percentage provides context that BMI alone cannot.
For practical UK health management, both metrics matter: use our free BMI calculator to get a starting point, then consider body fat percentage as part of a fuller picture. Your GP can advise on what these measurements mean for your personal health. Weight management — whether through lifestyle changes or prescription support like GLP-1 medications — aims to reduce fat mass whilst preserving muscle, making body composition tracking valuable alongside weight itself.
- 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 is a healthy body fat percentage for my age?
Healthy ranges vary by age and sex. For adults aged 20–40: men 8–19%, women 21–32%. For 41–60: men 11–22%, women 23–33%. For 60+: men 13–25%, women 24–35%. These are general guidelines; your GP can assess what's healthy for you individually.
How accurate are body fat calculators?
Estimation formulas using height, weight, and measurements are typically accurate to within 3–5%. DEXA scans and underwater weighing are most accurate but less accessible. For UK health tracking, estimation calculators provide useful trends — track changes over time rather than relying on single readings.
Can you lose body fat without losing weight?
Yes. If you gain muscle whilst losing fat, overall weight may stay similar whilst body composition improves significantly. This is common when starting strength training. Weight loss alone doesn't assures fat loss — lifestyle changes should include resistance exercise to preserve muscle.
Is body fat percentage more important than BMI?
Neither is perfect alone. BMI is a useful screening tool, but body fat percentage reveals composition. Use both: calculate your BMI above, then track body fat percentage for a fuller picture of your health progress.
How does body fat percentage relate to weight loss medications?
GLP-1 medications like Wegovy may support weight loss, and evidence suggests they help preserve muscle mass compared to diet alone. Tracking body fat percentage alongside weight loss helps ensure you're losing fat, not muscle — important for long-term health.
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.