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 Does A BMI Mean — An NHS Health Explanation
BMI stands for Body Mass Index — a simple measurement that compares your weight to your height to estimate whether you're at a healthy weight. The NHS uses BMI as a screening tool to assess weight-related health risks in adults. It's not a perfect measure of health on its own, but it's quick, accessible, and helps your GP understand whether your weight may affect your wellbeing. Understanding what your BMI means is the first step towards making informed health decisions. Use our free BMI calculator above to find your personal BMI instantly.
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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 formula is simple: divide your weight in kilograms by your height in metres squared. The result falls into one of these BMI categories UK adults should know about:
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5 to 24.9 — the target range recommended by NHS guidance
- Overweight: BMI 25.0 to 29.9 — increased health risks begin here
- Obese Class I: BMI 30.0 to 34.9 — significant health risks
- Obese Class II: BMI 35.0 to 39.9 — very high health risks
- Severely obese: BMI 40.0 and above — urgent intervention often needed
Important: If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy BMI range starts at 18.5 but peaks at 22.9 instead of 24.9. These adjusted thresholds reflect higher cardiovascular and diabetes risk in these populations at standard BMI levels.
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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 and When to Seek Help
The NHS recognises that weight management is important for long-term health. If your BMI falls into the overweight or obese categories, your GP can discuss your individual situation and may recommend support. The NHS follows a structured weight management pathway: Tier 1 (self-help and community programmes), Tier 2 (GP-based behaviour support), Tier 3 (specialist multidisciplinary services), and Tier 4 (bariatric surgery for severe cases). Even a 5–10% reduction in body weight can significantly improve blood pressure, blood sugar, and cholesterol levels. Contact your GP for a conversation about your BMI and health — they can assess your individual risks and discuss what support is available in your area.
- 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 does my BMI number actually mean?
Your BMI is a ratio of your weight to your height. A BMI of 20, for example, means your weight-to-height ratio falls into the "healthy weight" category according to NHS guidelines. It's a screening tool — not a diagnosis — but it helps identify whether your weight may increase health risks.
Is BMI accurate for everyone?
No. BMI has important limitations. It doesn't distinguish between muscle and fat, so athletes may have high BMI despite low body fat. It also doesn't account for where fat is stored or individual genetic factors. Your GP may use additional measurements like waist circumference alongside BMI.
What should I do if my BMI is above 25?
First, discuss your individual situation with your GP. Not everyone with a BMI above 25 needs intervention. Your doctor will consider your overall health, family history, and any weight-related conditions. If weight management is recommended, your GP can discuss lifestyle changes or refer you to NHS Tier 2 or Tier 3 support services.
Does BMI change with age?
The BMI formula itself doesn't change, but health outcomes at the same BMI may differ. Older adults may lose muscle naturally, making BMI a less reliable indicator. Your GP can advise what's appropriate for your age and circumstances.
Can I use a BMI calculator to check my health?
Yes — use our free BMI calculator on this page to find your personal BMI instantly. It's a useful starting point for understanding your weight-to-height ratio. However, BMI is just one piece of health information. Always consult your GP if you have concerns about your weight or 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.