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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BMI Classification Explained — UK Health Categories
BMI classification is a system used by the NHS and health professionals to categorise adult weight based on height and body mass. Understanding your BMI classification helps you assess whether your weight falls into a healthy range for your height. The standard BMI formula divides weight in kilograms by height in metres squared. Different BMI ranges correspond to specific health categories, though it's important to remember that BMI is a screening tool with limitations — it doesn't account for muscle mass or where fat is stored on your body. Use our free BMI calculator above to check your personal BMI instantly.
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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.
NHS BMI Classification Categories and Ranges
The NHS defines five main BMI categories for UK adults. A healthy BMI range sits between 18.5 and 24.9, which is associated with the lowest health risks. A BMI below 18.5 is classified as underweight. The overweight BMI threshold starts at 25.0 and continues to 29.9. Obesity begins at 30.0, divided into three classes: Class I (30.0–34.9), Class II (35.0–39.9), and Class III or severe obesity (40.0 and above).
It's crucial to note that these standard BMI categories UK apply to most adults. However, people of South Asian, Chinese, Black African, and Black Caribbean heritage have different risk profiles at the same BMI levels. For these groups, the NHS recommends lower thresholds: a healthy BMI range is 18.5 to 22.9, and obesity begins at 27.5 rather than 30.0. This reflects clinical evidence showing these populations face higher cardiovascular and metabolic risks at lower BMI values.
To find your BMI classification, use the BMI formula: weight (kg) ÷ height (m)². Our free weight converter above helps you switch between kilograms, stone, and pounds if needed.
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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.
BMI Limitations and Why Context Matters
While BMI classification is useful for population screening, it has significant limitations. BMI does not distinguish between muscle and fat — athletes with high muscle mass may have a high BMI but low body fat. Older adults may have reduced muscle, making BMI less accurate. BMI also ignores where fat is stored; abdominal fat carries higher health risks than fat distributed elsewhere.
For comprehensive health assessment, the NHS recommends pairing BMI with waist circumference measurement. Men with a waist over 94cm (37 inches) have increased cardiovascular risk; women over 80cm (31.5 inches) are at increased risk. Your GP can provide personalised advice about what your BMI classification means for your individual health, taking into account your medical history, fitness level, and other factors. Sustainable weight management combines healthy eating, physical activity, and regular health checks.
- 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 is the healthy BMI range according to NHS guidelines?
The standard NHS healthy BMI range is 18.5 to 24.9 for most adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower at 18.5 to 22.9. Your GP can advise what range is appropriate for you personally.
At what BMI does overweight classification begin in the UK?
In the UK, the overweight BMI threshold starts at 25.0 and continues to 29.9. Above 30.0 is classified as obese. These standard thresholds apply to most adults, though lower thresholds are recommended for certain ethnic groups.
Why does BMI classification differ for some ethnic groups?
Clinical research shows that South Asian, Chinese, Black African, and Black Caribbean adults develop type 2 diabetes and cardiovascular disease at lower BMI levels than other populations. The NHS therefore recommends lower BMI thresholds for these groups to better identify health risk earlier.
Is BMI the only measurement of a healthy weight?
No. BMI is a screening tool but has limitations. It doesn't account for muscle mass, body composition, or where fat is stored. The NHS recommends combining BMI assessment with waist circumference measurement and consultation with your GP for a complete picture.
How do I calculate my own BMI classification?
Use the BMI formula: weight in kilograms divided by height in metres squared. Or use our free BMI calculator on this page — simply enter your weight and height, and it will instantly show your BMI and classification category with NHS context.
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.