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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Calculating BMI for Athletes: Why Standard BMI Range Categories May Not Apply
BMI (body mass index) is a useful screening tool, but it has a significant limitation for athletes: it cannot distinguish between muscle and fat. An athlete with high muscle mass may have a BMI that falls into the "overweight" or even "obese" category according to NHS BMI range standards, despite having very low body fat and excellent health. This is why understanding BMI calculation alongside other fitness measures is essential for athletes. Use our free BMI calculator above to check your personal BMI, but remember that the result is just one part of the picture of your overall health and fitness.
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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.
Why BMI Calculation Can Mislead Athletes
The BMI formula is simple: weight (kg) ÷ height (m)². It treats all weight equally—whether from muscle or fat. Since muscle is denser than fat, athletes who have built significant muscle mass will often have a higher BMI than the NHS BMI categories suggest is "healthy," even though their body composition is excellent.
Standard NHS BMI categories are:
- Underweight: Below 18.5
- Healthy weight: 18.5–24.9
- Overweight: 25.0–29.9
- Obese: 30.0+
For many athletes—particularly strength athletes, rugby players, and bodybuilders—a BMI above 25 is completely normal and does not indicate poor health. A footballer with 8% body fat and a BMI of 28 is not overweight in any practical sense, despite what the standard categories suggest. This is why measuring body composition directly is far more valuable for athletic individuals than relying on BMI alone.
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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.
Better Fitness Measures Beyond BMI for Athletes
Rather than relying on BMI alone, athletes should track body fat percentage, which directly measures the proportion of your weight that is fat tissue. A healthy body fat range for athletic men is typically 6–13%, and for athletic women 14–20%. Other valuable measures include waist-to-height ratio (healthy below 0.5), waist circumference, and overall fitness metrics like VO2 max or strength benchmarks.
Your GP can refer you to sports medicine professionals who can assess body composition using methods like DEXA scans or bioelectrical impedance, which are far more informative than BMI for athletes. If you want a quick fitness check, convert your weight using our free weight converter and track progress over time alongside performance improvements—these together tell a much more complete story than BMI alone.
- 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 high BMI bad for athletes?
Not necessarily. Athletes with high muscle mass often have a higher BMI than standard NHS healthy weight categories, but this does not mean they are overweight or unhealthy. Body composition—not BMI—is what matters. Ask your GP or sports physician for a body fat assessment if you're concerned.
What's a good body fat percentage for athletes?
For athletic men, 6–13% body fat is typical; for athletic women, 14–20%. These ranges vary by sport and individual goals. General fitness aims are slightly higher: 18–24% for men, 25–31% for women. Your GP can help determine what's appropriate for you.
Can I use BMI if I'm a keen amateur athlete?
Yes, but with caution. BMI is a useful initial screening tool, but if you have significant muscle mass, it may not reflect your actual health. Use our BMI calculator as a starting point, then discuss your individual circumstances with your GP or a sports physician.
What's better than BMI for measuring athletic fitness?
Body fat percentage, waist-to-height ratio, waist circumference, and performance metrics are all more informative for athletes. DEXA scans and bioelectrical impedance analysis can measure body composition accurately. Your GP can arrange these assessments.
Should athletes aim for a "healthy" BMI?
Not necessarily. Many healthy athletes fall outside standard healthy BMI ranges due to muscle mass. Focus instead on body composition, cardiovascular fitness, strength, and how you feel. Your GP can help you set realistic, health-focused goals.
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.