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 To Compute Body Fat Percentage
Body fat percentage measures how much of your weight is fat versus lean mass like muscle and bone. Unlike BMI, which can't distinguish between muscle and fat, body fat percentage gives a clearer picture of your actual composition. The NHS and health professionals increasingly recognise body composition as important alongside BMI for understanding overall health. This guide explains the main methods to compute your body fat percentage, what healthy ranges look like, and how it complements other health measures like the BMI calculator available on this page.
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.
Methods To Compute Your Body Fat Percentage
Several practical methods exist to compute body fat percentage, ranging from simple to more precise:
- Skinfold callipers: A trained professional measures skin folds at specific body sites (usually three to seven locations) and uses a formula to estimate fat percentage. Accuracy depends heavily on the technician's skill.
- Bioelectrical impedance analysis (BIA): A device sends a harmless electrical current through your body to estimate fat mass. Common in gym scales and body composition analysers. Results vary with hydration level.
- DEXA scan: The gold standard for accuracy. Uses low-dose X-rays to measure bone density, fat mass, and lean mass separately. Available through some private health clinics and NHS hospitals.
- Hydrostatic weighing: You're weighed underwater to calculate body density and fat percentage. Highly accurate but less accessible in the UK.
- Online calculators: Simple formulas using height, weight, age, and measurements. Less precise than professional methods but convenient for tracking trends over time.
For most people tracking progress, a combination method works well: use an online calculator for baseline estimates, track changes with a home BIA scale, and have professional measurements annually.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 And Why BMI Alone Isn't Enough
Healthy body fat percentage varies significantly by age and sex. Women typically have a healthy range of 21–24% body fat, while men's healthy range is 14–17%. Essential fat (needed for organ function) is 10–13% for women and 2–5% for men. These ranges differ from BMI categories because someone with high muscle mass—like an athlete—can have a high BMI but low, healthy body fat percentage.
This is why body composition matters: BMI alone cannot distinguish muscle from fat. A person at BMI 27 (technically "overweight" by NHS standards) with 18% body fat is in better metabolic health than someone at BMI 25 with 35% body fat. Using our free BMI calculator alongside body fat assessment gives you a complete picture. Your GP can advise on what healthy composition means for your individual circumstances, especially if you have weight-related health conditions.
- 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 between muscle and fat. Body fat percentage shows the actual proportion of fat in your body. Someone very muscular might have a high BMI but low body fat percentage. Both measures are useful together—BMI is a quick screening tool, while body fat percentage reveals your actual composition.
What body fat percentage should I aim for?
UK health guidance suggests women aim for 21–24% and men for 14–17% in the "fitness" category. However, healthy ranges vary by age, genetics, and individual health. Your GP or a registered dietitian can advise on what's appropriate for you based on your age, health conditions, and goals.
Can I compute my body fat percentage at home?
Yes, using online calculators with your height, weight, age, and waist/hip measurements. Results are estimates and less precise than professional methods like DEXA scans or skinfold measurements. Home bioelectrical impedance scales offer reasonable tracking for trends, though accuracy varies with hydration and body position.
Is body fat percentage more important than weight?
Not necessarily more important, but equally important. Weight, BMI, body composition, and waist circumference all tell different parts of the story. For health assessment, your GP considers all these measures together, plus your fitness level and medical history.
How often should I measure my body fat percentage?
Monthly or quarterly is reasonable for tracking progress if you're working on health improvements. More frequent measurements (weekly) aren't usually helpful because natural fluctuations from hydration, hormones, and digestion can mask real changes. Consistency in measurement method matters more than frequency.
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.