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
BMI and Muscle Mass — What the NHS Really Says
BMI (body mass index) is a useful screening tool, but it has a significant limitation: it cannot tell the difference between muscle and fat. Someone who is very muscular may have a high body mass index, yet be in excellent health. The NHS recognises this limitation and recommends using BMI alongside other measurements — particularly waist circumference — to get a complete picture of your weight and health. Our free BMI calculator above can help you find your personal BMI, but this guide explains why your GP may want to look at more than just that number.
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.
NHS Approach to BMI — Why It's Just Part of the Picture
The NHS uses the standard BMI categories (healthy: 18.5–24.9, overweight: 25–29.9, obese: 30+), but NHS guidance is clear that BMI alone is not enough for assessing health risk. The healthy BMI range UK standard applies to most adults, yet a muscular athlete or gym enthusiast could fall into the "overweight" or "obese" category despite having low body fat.
- Muscle tissue is denser than fat tissue, so it weighs more per unit volume
- Two people at the same weight and height can have completely different body compositions
- Waist circumference is more predictive of cardiovascular risk than BMI alone
- For men: increased risk over 94cm, high risk over 102cm; for women: increased risk over 80cm, high risk over 88cm
NICE (National Institute for Health and Care Excellence) supports using both BMI and waist measurement when assessing weight-related health risks. This combined approach gives NHS professionals a clearer picture of where excess fat is stored — which matters more for health than overall BMI.
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.
When to Talk to Your GP About BMI and Body Composition
If your BMI suggests you're overweight or obese but you're very muscular or athletic, your GP can assess your individual risk using additional information: waist circumference, blood pressure, cholesterol, blood sugar, and family history. Your GP may refer you to the NHS weight management pathway if needed.
- Tier 1: self-help and community programmes
- Tier 2: primary care behaviour change support
- Tier 3: specialist multidisciplinary weight management services
- Tier 4: bariatric surgery for severe obesity with complications
Use our free BMI calculator and weight converter above to track your measurements. If you're concerned about your weight or body composition, book an appointment with your GP who can give personalised advice based on your complete health picture.
- 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.
Does having more muscle mean my BMI will be inaccurate?
Yes. BMI measures total body weight divided by height squared, so it can't distinguish muscle from fat. Muscular individuals — athletes, gym-goers, a UK pharmacy workers — often have higher BMI despite low body fat. This is why the NHS recommends checking waist circumference and other health markers alongside BMI, not instead of it.
What does the NHS recommend instead of just checking BMI?
The NHS recommends a combined approach: calculate your BMI using the body mass index formula, then measure your waist circumference. Waist measurement is more predictive of cardiovascular and metabolic risk because it indicates where excess fat is stored. Your GP may also check blood pressure, cholesterol, and blood sugar to assess overall health risk.
What's a healthy waist circumference according to NHS guidance?
For men: under 94cm (37 inches) is ideal, 94–102cm indicates increased risk, over 102cm indicates high risk. For women: under 80cm (31.5 inches) is ideal, 80–88cm indicates increased risk, over 88cm indicates high risk. These thresholds apply to most UK adults and indicate where fat storage poses the greatest health risk.
If I'm muscular with a high BMI, do I still need to see my GP?
Even if you're very muscular, it's worth discussing your health with your GP, especially if you have other risk factors like high blood pressure, family history of diabetes, or weight-related health conditions. Your GP can assess your complete health picture and advise whether weight management or other interventions are needed.
How accurate is BMI as a health screening tool overall?
BMI is a useful starting point but has known limitations: it ignores muscle mass, doesn't account for age or bone density, and varies by ethnicity (South Asian, Black African, and Chinese adults face higher health risks at lower BMI levels). The NHS treats BMI as one of several screening tools, never as the only measure of 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.