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
Obesity Classification By BMI — What the Categories Mean
Obesity classification by BMI is how the NHS and healthcare professionals categorise weight-related health risk in UK adults. Your BMI (body mass index) falls into different categories depending on your weight and height, and these categories help determine whether excess weight may affect your health. Understanding where you fall on the BMI scale is the first step towards making informed health decisions. MyWeightCheck's free BMI calculator makes it easy to find your personal BMI and understand what it means for you.
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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 Obesity Classification
The NHS uses five main BMI categories to classify weight status in UK adults. According to the BMI formula (weight in kg ÷ height in metres squared), these are:
- 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 and above
A healthy BMI according to NHS guidelines sits between 18.5 and 24.9. Once your BMI reaches 30 or above, you enter the obese classification, which indicates increased health risks including type 2 diabetes, cardiovascular disease, and certain cancers. The NHS BMI categories are evidence-based and form the foundation of UK weight management guidance. Calculate your personal BMI now using the free BMI calculator on this page to see where you fall.
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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 What Else Matters
While BMI is a useful screening tool, it has important limitations. BMI limitations include the fact that it does not distinguish between muscle and fat—an athlete may have a high BMI but low body fat. BMI also does not account for where fat is stored on your body, which matters for health risk assessment. The NHS recommends using waist circumference alongside BMI: for men, over 94cm (37 inches) indicates increased risk; over 102cm (40 inches) indicates high risk. For women, over 80cm (31.5 inches) indicates increased risk; over 88cm (34.5 inches) indicates high risk. Age, ethnicity, and muscle mass all affect what your BMI truly means. Your GP can give you personalised health advice based on your full health picture, not just your BMI number alone.
- 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 obesity classification by BMI mean for my health?
Obesity classification indicates increased risk of weight-related health conditions like type 2 diabetes, heart disease, and certain cancers. However, BMI is just one measure. Your GP can assess your individual health risk based on your full health history, family history, fitness level, and other factors. Lifestyle changes and, where appropriate, medical support can help reduce health risks.
Is the BMI classification the same for all UK adults?
For most UK adults of European heritage, the NHS BMI ranges apply as listed above. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at lower BMI levels. Discuss your personal BMI thresholds with your GP.
I have a high BMI but feel healthy—should I be worried?
BMI is a screening tool, not a complete health assessment. Some people with higher BMI are metabolically healthy, whilst others with lower BMI may have health risks. Weight-related health problems develop over time and may not cause symptoms you notice. Your GP can assess your individual risk through blood tests, blood pressure checks, and discussion of your health history.
Can I use BMI to check if I'm overweight?
Yes, BMI is the standard UK measure for determining whether you fall into the overweight category (BMI 25–29.9). However, BMI does not account for muscle mass or fat distribution. Use our free BMI calculator to find your BMI, then discuss the result with your GP for personalised guidance on your weight and health.
What's the difference between obese and overweight BMI classification?
Overweight is classified as BMI 25.0–29.9, whilst obese begins at BMI 30.0. The NHS classifies obesity further into three classes based on increasing health risk. The boundary at BMI 30 is where health risks from excess weight increase notably. However, health risk exists across a spectrum—even modest weight loss can improve health outcomes at any BMI level.
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.