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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Normative BMI Data — What the Numbers Mean
Normative BMI data refers to the standard weight ranges and categories used by health professionals to assess whether an adult's weight falls within a healthy range. In the UK, the NHS uses a consistent BMI formula and categories based on large population studies. Understanding these reference values helps you interpret your own BMI and see how your weight compares to national health guidelines. Your personal BMI is calculated from your height and weight, and falls into one of five NHS categories—each carrying different health implications. Use our free BMI calculator above to check your personal BMI instantly and see which category you fall into.
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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 Reference Ranges
The NHS BMI formula divides adults into five standard categories based on extensive population research. These normative ranges help GPs and health professionals identify health risks associated with excess weight. The healthy BMI range for most UK adults is 18.5 to 24.9—this range represents the weight zone where obesity-related health risks are lowest.
- Underweight (Below 18.5): May indicate nutritional deficiency or underlying health issues
- Healthy weight (18.5–24.9): Lowest risk of weight-related disease
- Overweight (25.0–29.9): Increased risk of type 2 diabetes and cardiovascular disease
- Obese Class I (30.0–34.9): Significantly elevated health risks
- Obese Class II (35.0–39.9): Very high health risks
- Severely obese (40.0+): Severe health risks including diabetes, heart disease, and certain cancers
These bmi categories uk are derived from research showing when health complications typically begin. However, these are population averages—your individual risk depends on many other factors including age, fitness level, family history, and where you carry weight.
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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.
Ethnicity-Adjusted Thresholds and BMI Limitations
The NHS recognises that the standard BMI ranges do not apply equally to all populations. People of South Asian, Chinese, Black African, and Black Caribbean heritage have higher risks of type 2 diabetes and cardiovascular disease at lower BMI levels, so adjusted thresholds apply: healthy weight is 18.5–22.9, overweight starts at 23.0, and obese begins at 27.5. This is crucial because using standard ranges alone would miss health risks in these groups.
BMI is a useful screening tool but has significant bmi limitations. It cannot distinguish between muscle and fat—athletes may have high BMI but low body fat. BMI also ignores where fat is stored; waist circumference is equally important. Consult your GP for personalised health assessment alongside BMI. Use the weight converter on this page to check your weight in different units, and our progress tracker to monitor changes over time.
- 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 normative BMI range for a healthy adult in the UK?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. This range is based on large population studies showing when obesity-related health risks increase significantly. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is slightly lower: 18.5 to 22.9. Your GP can advise if your individual circumstances warrant adjustment.
Why are BMI categories different for certain ethnic groups?
Research shows that people from South Asian, Chinese, Black African, and Black Caribbean backgrounds have higher risks of type 2 diabetes, heart disease, and stroke at lower BMI levels compared to other groups. The NHS adjusted the thresholds to reflect this biological reality and ensure these populations aren't missed when screening for weight-related health risks.
What does normative BMI data actually measure?
Normative BMI data represents the standard weight ranges observed across large populations, linked to health outcomes. It's derived from decades of research showing at which weights obesity-related diseases (diabetes, heart disease, cancer) become more common. The data helps identify population-level patterns, though individual health depends on many other factors beyond BMI alone.
Is BMI a perfect measure of health?
No. BMI cannot distinguish muscle from fat, doesn't account for where fat is stored, and ignores age, fitness level, and family history. Someone very muscular may have a high BMI but be perfectly healthy. Waist circumference is equally important—measure around your natural waist; over 94cm (men) or 80cm (women) indicates increased risk. Always discuss your personal health with your GP.
How do I calculate my BMI using the normative formula?
The BMI formula is weight in kilograms divided by height in metres squared: BMI = kg ÷ (height in m)². For example, someone weighing 70kg and 1.73m tall: 70 ÷ (1.73 × 1.73) = 23.4 BMI (healthy weight). Our free BMI calculator above does this instantly—just enter your height and weight in your preferred units.
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.