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
Muscle Calculator — Understand Your Body Composition
A muscle calculator helps you estimate how much of your body weight is lean muscle versus fat, which is important information that BMI alone cannot provide. While a BMI calculator tells you whether your weight is in a healthy range for your height, it does not distinguish between muscle and fat. A muscle calculator uses your height, weight, age, and sex to estimate your body composition, giving you a more complete picture of your health. This NHS health information is particularly useful if you are active, building muscle through exercise, or managing your weight.
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 a Muscle Calculator Works
A muscle calculator uses predictive formulas based on clinical research to estimate your body composition from basic measurements. The most common method is the Katch-McArdle formula, which estimates your basal metabolic rate (BMR) and uses that to calculate lean body mass and fat percentage.
Key measurements needed:
- Height (in cm or feet and inches)
- Weight (in kg or stone and pounds)
- Age in years
- Sex (male or female)
Important limitation: Muscle calculators provide estimates only. They are less accurate than DEXA scans or hydrostatic weighing, but are practical for home use. Individual results vary based on genetics, training history, and body frame size. Our free weight converter and BMI calculator complement muscle calculation by showing your current weight status and healthy weight range according to NHS guidance.
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.
UK Guidance and Next Steps
Body composition changes with age and activity level. Athletes typically have higher muscle percentage and lower body fat percentage than sedentary adults. Men generally have naturally higher muscle mass than women due to testosterone, while women typically have a higher body fat percentage even at healthy weights.
Using your results: If your muscle calculator shows lower lean mass than expected, increasing strength training and protein intake can help build muscle over time. If body fat percentage is elevated according to NHS healthy weight UK standards, creating a calorie deficit through diet and physical activity may help. Weight management that preserves muscle mass is more sustainable than rapid weight loss. Consider combining muscle calculator results with our weight management tools and nhs health advice for a complete picture of your fitness and wellness goals.
- 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.
Is a muscle calculator more accurate than BMI?
Both serve different purposes. A BMI calculator shows if your weight is healthy for your height, while a muscle calculator estimates body composition. Together they give better insight than either alone. A muscle calculator is more useful if you are very muscular or sedentary, as BMI may misclassify athletes or less active individuals. For NHS health guidance, discuss results with your GP.
Can I use a muscle calculator at home?
Yes. Free online muscle calculators require only basic measurements: height, weight, age, and sex. They are not as precise as clinical methods like DEXA scans, but they are practical and free. Our muscle calculator is designed for UK adults using stone and pounds or kg. Results are estimates and individual variation is normal.
What is a healthy body fat percentage for adults?
According to fitness health guidance, healthy ranges are: women 18–25%, men 10–20%. Athletes may have lower percentages; sedentary adults often have higher. Body fat ranges also depend on age. These are general guidelines; your GP can advise what is healthy for your individual circumstances.
How often should I use a muscle calculator to track progress?
Once monthly is reasonable if you are tracking fitness progress through training. More frequent use (weekly) may show normal fluctuations due to hydration and digestion rather than real change. Combine muscle calculator tracking with weight converter logs and weight loss management notes for best results.
Does muscle calculator work for older adults?
Yes, but accuracy may decrease with age as formulas were developed using younger populations. Older adults experience natural muscle loss (sarcopenia), so tracking muscle mass becomes more important. NHS health advice recommends strength training at all ages. A muscle calculator alongside your GP's personalised guidance provides useful context for healthy ageing.
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.