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
Body Mass Check — What Your Body Composition Means
A body mass check goes beyond simple weight measurement to assess your overall body composition — the balance between lean body mass, muscle, bone, and body fat. Unlike a basic weight scale, understanding your body composition gives you a clearer picture of your actual health status. MyWeightCheck provides free tools to help you assess where you stand and what healthy ranges look like for UK adults.
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 to Interpret Your Body Mass Calculator Results
The body mass check calculator on this page provides several key metrics to assess your health. Body fat percentage is the proportion of your total body weight that is fat tissue — it varies significantly between men and women due to hormonal differences. According to fitness guidelines, women typically have a healthy body fat range of 21–24%, while men fall in the 14–17% range for fitness levels. For general health (the "acceptable" category), women should aim for 25–31%, and men 18–24%.
- Lean body mass represents everything except fat — muscle, bones, organs, and water. This is particularly important because muscle tissue is metabolically active and supports overall fitness.
- Healthy body fat ranges vary by age, gender, and fitness level. Essential fat for women is 10–13%; for men, 2–5%. Higher percentages don't mean poor health — context matters.
- Results from this calculator are estimates based on standard formulas. A healthcare professional can provide more precise measurement using methods like DEXA scans or hydrostatic weighing.
Use our free BMI calculator alongside this tool to get a fuller picture of your health status — BMI tells you about weight relative to height, while body composition reveals what that weight actually consists of.
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.
Body Fat vs BMI — When Each Metric Matters Most
Body composition and BMI serve different purposes. BMI uses height and weight to screen for health risk categories, while body fat percentage reveals whether your weight comes from muscle or fat. A person with a high BMI might have significant lean body mass (like an athlete), while another might have a normal BMI but high body fat percentage and visceral fat (internal belly fat that carries greater health risks).
- BMI is quick and free to calculate — ideal for screening populations. Use our free BMI calculator above for gradual improvement.
- Body fat percentage is more accurate for individuals but requires additional measurements or technology.
- Waist circumference is also valuable: men over 94cm (37 inches) face increased cardiovascular risk; women over 80cm (31.5 inches) face similar risk.
For a complete health picture, consider all three metrics together — they complement rather than replace each other.
- 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 women in the UK?
According to fitness standards, healthy body fat for women is 21–24% (fitness level) or 25–31% (acceptable/general health). Essential fat ranges from 10–13%. These are guidelines only — your GP can advise on what's appropriate for your individual health situation.
Is body fat percentage more accurate than BMI?
Body fat percentage reveals composition (muscle vs fat), while BMI screens for health risk categories based on height and weight. Neither is universally "better" — they measure different things. Using both, along with waist circumference, gives the clearest picture. Our BMI calculator can help with that assessment.
What does lean body mass mean?
Lean body mass is everything in your body except fat tissue — including muscle, bone, organs, and water. It's metabolically active, meaning it burns calories at rest. Building lean mass through exercise and adequate protein supports long-term health and sustainable weight management.
Why do men and women have different healthy body fat ranges?
Women have higher essential fat due to hormonal and reproductive factors (10–13% vs 2–5% for men). Beyond essential fat, ranges vary by age and fitness level. These are general guidelines; your personal healthy range depends on your genetics, age, fitness level, and overall health.
How does visceral fat differ from regular body fat?
Visceral fat surrounds internal organs and carries greater health risks — it's linked to type 2 diabetes and cardiovascular disease. You can't feel it (it's internal). Waist circumference is a good proxy for visceral fat risk. A GP can advise if your measurements suggest increased risk.
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.