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
What Is Your Workout BMI and Why It Matters
If you exercise regularly, you may wonder whether your BMI tells the full story about your health. BMI is a useful screening tool used by the NHS, but it has important limitations — especially for people who work out. This guide explains what NHS guidance says about BMI, how the bmi formula works, and why muscle matters. You'll also learn when to seek GP support for your health and fitness goals. Use our free BMI calculator above to check your personal BMI instantly, then read on to understand what it means for your individual 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.
NHS BMI Categories and What They Mean
The NHS BMI categories are the standard health thresholds used across UK healthcare:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese (Class III): BMI 40.0+
The bmi formula is simple: weight (kg) ÷ height (m)². This calculation is the same for everyone, whether you exercise or not. However, a key bmi limitation is that it cannot distinguish between muscle and fat. Someone who works out regularly may have a higher BMI due to increased muscle mass, even if their body fat percentage is healthy. NICE guidance recommends using BMI alongside other measurements — particularly waist circumference — to get a fuller picture of health risk.
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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.
NHS Weight Management Support and When to Seek Help
The NHS offers a structured weight management pathway across four tiers. Tier 1 includes self-help tools, digital programmes, and community support. Tier 2 involves your GP and behaviour change programmes like the NHS Weight Loss Plan. Tier 3 is specialist multidisciplinary weight management services — where prescription medications may be offered if appropriate. Tier 4 covers bariatric surgery for severe obesity with serious health complications. Your GP can assess your individual situation and refer you to the right support. If you're exercising regularly but still concerned about your healthy bmi range or overall health, a conversation with your GP is always a good starting point. Track your progress over time using our free progress tracker to see how your health metrics change with consistent exercise.
- 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 muscle count as fat in BMI calculations?
No. BMI cannot distinguish between muscle and fat — it only measures total weight relative to height. If you exercise regularly and build muscle, your BMI may be higher than sedentary people at the same height, even if your body fat percentage is healthy. This is why the NHS recommends checking waist circumference and overall fitness alongside BMI.
What's the difference between BMI and body composition?
BMI is a simple weight-to-height ratio. Body composition measures the actual percentage of fat versus muscle. Two people with identical BMI can have very different body compositions. Someone with regular exercise may have the same BMI as someone sedentary, but with much lower body fat and more muscle mass.
Should I ignore my BMI if I work out regularly?
No — BMI is still a useful health screening tool. However, it's only part of the picture. Use our free BMI calculator to check your category, but also consider your waist circumference, how you feel, your fitness level, and any weight-related health conditions. Discuss your individual health with your GP.
What does NHS guidance say about exercise and weight?
The NHS recommends at least 150 minutes of moderate aerobic activity weekly for adults, plus strength training twice weekly. Regular exercise supports heart health, weight management, and mental wellbeing — even if it doesn't dramatically lower BMI. Many people find the best approach combines exercise with gradual dietary changes.
Can I have a healthy BMI but still need to lose weight?
Yes, in some cases. If your BMI falls in the healthy range (18.5–24.9) but your waist circumference is high, or you have weight-related health conditions like prediabetes, your GP may recommend modest weight loss alongside continued exercise and lifestyle support.
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.