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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Understanding Muscle Mass Percentage — UK Health Guide
Muscle mass percentage is the proportion of your body weight that is muscle tissue. Unlike BMI, which doesn't distinguish between muscle and fat, muscle mass percentage gives a more complete picture of your body composition. In the UK, understanding your muscle mass percentage alongside BMI and weight management is increasingly recognised as important for long-term health. The NHS and health professionals across the UK use body composition assessment as part of a comprehensive approach to weight health.
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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.
UK Reference Ranges for Muscle Mass Percentage
Healthy muscle mass percentage varies by age and sex. According to fitness and body composition research aligned with UK health standards, the following ranges are considered healthy:
- Men aged 20–39: 39–47% muscle mass
- Men aged 40–59: 35–43% muscle mass
- Men aged 60+: 31–39% muscle mass
- Women aged 20–39: 34–40% muscle mass
- Women aged 40–59: 30–36% muscle mass
- Women aged 60+: 26–32% muscle mass
Muscle mass naturally declines with age — this process is called sarcopenia. The NHS recognises this as a genuine health concern in older adults, as loss of muscle increases fall risk and reduces independence. Maintaining adequate muscle mass through resistance exercise and adequate protein intake is a key part of healthy weight management and ageing well in the UK.
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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.
Muscle Mass vs BMI — Why Both Matter for UK Health
Your BMI (body mass index) tells you whether your weight sits in a healthy range according to NHS guidelines — but it doesn't tell you whether that weight is muscle or fat. Two people at the same BMI can have very different body compositions. For example, a trained athlete and a sedentary person can both have a BMI of 25, yet the athlete may have 45% muscle mass whilst the other has 20%. This is why using our free BMI calculator alongside body composition assessment gives a much clearer picture of your health. Your GP can refer you for DEXA scans or other body composition analysis if needed, particularly if you have concerns about muscle loss or weight management outcomes.
- 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 muscle mass percentage?
Muscle mass percentage is the proportion of your total body weight that is muscle tissue, expressed as a percentage. Unlike BMI, which only uses height and weight, muscle mass percentage reflects actual body composition. It's measured using methods like DEXA scans, bioelectrical impedance analysis (BIA), or fitness trackers. A higher muscle mass percentage generally correlates with better metabolic health and strength.
Is muscle mass percentage more important than BMI?
Both are useful but for different reasons. BMI is a population-level screening tool used by the NHS to identify health risk groups. Muscle mass percentage tells you your actual body composition — whether your weight is mostly muscle or fat. For comprehensive health assessment, both matter. Your GP can advise which is most relevant for your individual situation and health goals.
How can I increase my muscle mass percentage in the UK?
Resistance exercise (strength training, weight lifting) is the most effective way to build muscle. The NHS recommends at least two days per week of muscle-strengthening activities for adults. Adequate protein intake is also essential — aim for around 1.6g per kilogram of body weight daily if actively building muscle. Your GP or a registered dietitian can provide personalised advice. Use our free weight converter and BMI calculator to track your progress alongside body composition changes.
Does muscle mass percentage decline with age in the UK?
Yes, muscle naturally declines from around age 30 onwards — approximately 3–8% per decade after age 30. The NHS recognises this (sarcopenia) as a serious health concern in older adults. Regular resistance exercise, adequate protein, and good nutrition can slow this decline significantly. Staying physically active is one of the most important factors in maintaining muscle and independence as you age.
Can I measure muscle mass percentage at home?
Some methods give approximate estimates — smart scales with bioelectrical impedance analysis (BIA) are widely available in the UK. However, these are less accurate than clinical methods like DEXA scans. For a precise measurement, ask your GP about referral to a NHS or private body composition service. BIA scales are helpful for tracking trends over time, but shouldn't be relied on as absolute measurements.
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