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 BMI Constitutes Obesity?
In the UK, a BMI of 30.0 or above constitutes obesity according to NHS guidelines. Obesity is classified into three categories: Class I (BMI 30.0–34.9), Class II (BMI 35.0–39.9), and Class III or severe obesity (BMI 40.0 and above). However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds, with obesity starting at BMI 27.5 due to higher health risks at lower weights. Use our free BMI calculator above to check your personal BMI and understand where you fall within these NHS categories.
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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 Obesity Thresholds
The NHS BMI categories define obesity as a BMI of 30.0 or higher. The bmi formula is straightforward: weight in kilograms divided by height in metres squared (kg ÷ m²). This simple calculation places adults into distinct health categories:
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9 (this is the overweight bmi threshold in the UK)
- 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
For adults of South Asian, Chinese, or Black African and Caribbean backgrounds, the healthy bmi upper limit is 22.9 rather than 24.9, and obesity begins at BMI 27.5. This ethnicity-adjusted guidance reflects evidence that these populations face elevated cardiovascular and metabolic disease risk at lower BMI levels compared to European populations.
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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 categories uk provide a useful screening tool, bmi limitations are important to understand. BMI does not distinguish between muscle and fat—athletes may have a high BMI but low body fat percentage. It also doesn't account for where fat is stored; central abdominal fat carries greater health risk than fat distributed elsewhere. Age, bone density, and pregnancy also affect BMI accuracy. For a complete health picture, your GP may also assess your waist circumference (over 94cm for men or 80cm for women indicates increased health risk) and consider your overall medical history, family history, and lifestyle factors alongside your BMI reading.
- 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.
At what BMI am I considered obese in the UK?
According to NHS guidelines, a BMI of 30.0 or above constitutes obesity. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, obesity is classified as a BMI of 27.5 or above due to higher health risks at lower BMI levels in these populations.
What is the difference between overweight and obese BMI?
In the UK, overweight is defined as a BMI between 25.0 and 29.9, while obesity begins at BMI 30.0. Obesity is further divided into three classes: Class I (30.0–34.9), Class II (35.0–39.9), and Class III or severe obesity (40.0+). Each category carries different health implications.
How do I calculate my BMI to check if I'm obese?
Use the BMI formula: weight in kilograms divided by height in metres squared (kg ÷ m²). For example, if you weigh 85kg and are 1.75m tall: 85 ÷ (1.75 × 1.75) = 27.8 (overweight). Our free BMI calculator above does this instantly for you.
Why do people of South Asian heritage have different obesity thresholds?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations have higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels compared to European populations. The NHS therefore recommends lower BMI thresholds for these groups: a healthy BMI up to 22.9 and obesity from 27.5 onwards.
Does a high BMI always mean I'm unhealthy?
BMI is a screening tool, not a diagnostic measure. It doesn't account for muscle mass, fat distribution, age, or overall fitness. Someone with high muscle mass may have a high BMI but be very fit. Your GP can assess your individual health using BMI alongside other factors like waist circumference, blood pressure, and blood tests for a complete picture.
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.