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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What Is Normative Data for BMI and Why Does It Matter?
Normative data for BMI refers to the standard reference ranges and population averages used by the NHS to assess whether a person's weight falls within a healthy range. Rather than looking at individual numbers in isolation, normative data compares your BMI against what is typical and healthy for UK adults. The NHS uses specific BMI thresholds based on clinical evidence to help identify health risks and guide weight management decisions. Understanding these normative ranges helps you interpret your own BMI in a meaningful, context-specific way that reflects current UK health guidance.
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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 Categories and Official UK Thresholds
The NHS defines five standard BMI categories that serve as normative reference points for UK adults:
- Underweight: BMI below 18.5 — may indicate nutritional risk
- Healthy weight: BMI 18.5–24.9 — associated with lowest health risk
- Overweight: BMI 25.0–29.9 — increased risk of weight-related conditions
- Obese (Class I): BMI 30.0–34.9 — elevated health risks
- Obese (Class II): BMI 35.0–39.9 — significantly elevated risks
- Severely obese (Class III): BMI 40.0+ — substantial health risks requiring intervention
These categories are based on clinical research linking BMI to cardiovascular disease, type 2 diabetes, and other weight-related conditions. However, the NHS also recognises that ethnicity affects risk at the same BMI. Adults of South Asian, Chinese, Black African, and Black Caribbean heritage have lower recommended thresholds — the healthy weight range for these populations is BMI 18.5–22.9, with overweight starting at BMI 23.0. This reflects evidence that these communities face higher metabolic and cardiovascular risk at lower BMI levels. Use our free BMI calculator above to check your personal BMI and see which category applies to you.
Clinically BackedWeight Loss
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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 Pathway and When to Seek Help
The NHS provides a structured tier system for weight support. Tier 1 includes self-help tools and community programmes — like this free weight converter and BMI calculator. Tier 2 involves your GP offering lifestyle advice and behaviour change support. Tier 3 provides access to specialist weight management services with multidisciplinary teams (dietitians, psychologists, medical staff), where prescription medications like Mounjaro or Wegovy may be considered. Tier 4 is bariatric surgery for severe obesity with significant health complications.
You should contact your GP if your BMI consistently falls in the obese range, you have weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea), or you've struggled with weight loss despite lifestyle efforts. Your GP can assess your individual health picture and refer you to appropriate support — normative BMI data is just one tool they'll consider alongside your personal health history, waist circumference, and cardiovascular risk factors.
- 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 average BMI of UK adults?
According to ONS data, the average UK adult man has a BMI of approximately 27.9, and the average UK adult woman has a BMI of approximately 27.4. Both averages fall in the "overweight" category (25.0–29.9), reflecting that over 63% of UK adults are overweight or obese.
Why does the NHS use different BMI thresholds for different ethnicities?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher cardiovascular and metabolic risk at lower BMI levels compared to white European populations. The NHS therefore recommends lower thresholds for these groups — healthy weight starts at BMI 18.5–22.9 instead of 18.5–24.9.
What does normative BMI data tell me that my individual BMI number doesn't?
Normative data places your BMI within population ranges and health risk categories established by clinical research. Your individual BMI (e.g., 28) tells you a number; normative data tells you that 28 falls in the "overweight" range and indicates increased health risk compared to the healthy range of 18.5–24.9.
Are there limitations to using normative BMI data for health assessment?
Yes — BMI does not distinguish muscle from fat, does not account for where fat is stored, and is less accurate in elderly people or pregnant women. The NHS recommends using BMI alongside waist circumference measurement (over 94cm in men or 80cm in women indicates increased risk) and discussing your overall health picture with your GP.
When should I use normative BMI data to decide if I need help with weight management?
If your BMI falls consistently in the overweight (25–29.9) or obese (30+) range, and especially if you have weight-related health conditions like high blood pressure or prediabetes, discuss this with your GP. They can use normative data alongside your personal health context to recommend appropriate support, which may include lifestyle changes, tier 2 services, or referral to specialist tier 3 weight management teams.
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.