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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Understanding BMI Class Obesity and NHS Weight Categories
BMI class obesity refers to the NHS weight categories used to assess whether excess weight increases health risks. The NHS classifies obesity into three categories based on your BMI (body mass index), starting at BMI 30 and above. Understanding which BMI class you fall into helps you and your GP assess your health risk and discuss whether weight management support would be beneficial. Use our free BMI calculator above to find your personal BMI instantly, then compare it against NHS guidelines to understand what it means for your health.
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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 Classification
The NHS uses a standardised BMI formula to classify weight categories across the UK population. Your BMI range determines whether you fall into the healthy weight, overweight, or obese category. According to NHS guidance, BMI obesity begins at 30.0 and above. Within obesity, there are three classes: 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).
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds due to higher health risks at lower BMI levels. For these groups, overweight starts at BMI 23.0 and obesity at BMI 27.5. Your GP can discuss which thresholds are most relevant to your individual health profile and family history. Remember that BMI has limitations—it doesn't distinguish muscle from fat, so athletes may have a high BMI but low body fat.
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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 Support and When to Seek Help
If your BMI falls into the obesity range (30 or above, or 27.5+ for certain ethnic groups), your GP can discuss weight management options with you. The NHS weight management pathway starts with tier 1 support—self-help resources, digital tools, and community programmes. If you need more support, your GP can refer you to tier 2 or tier 3 specialist weight management services, where trained healthcare professionals assess your individual situation. Even a 5–10% reduction in body weight can meaningfully improve blood pressure, blood sugar control, and reduce strain on your joints.
Don't wait until obesity causes complications. Speak with your GP if you're concerned about your weight, especially if you have related health conditions like high blood pressure, type 2 diabetes, or sleep apnoea. Our free weight converter can help you track your weight across UK measurements (stone, lbs, and kg) as you progress.
- 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 difference between overweight and obese BMI classes?
According to NHS guidance, overweight is BMI 25.0–29.9, while obesity begins at BMI 30.0. Obesity is further divided into Class I (30.0–34.9), Class II (35.0–39.9), and Class III or severe obesity (40.0+). Each class represents increasing health risk, and your GP may recommend different interventions depending on your class and overall health.
Are the NHS BMI obesity thresholds the same for everyone in the UK?
No. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds. Overweight for these groups is BMI 23.0–27.4, and obesity begins at BMI 27.5. This reflects evidence that these populations face higher cardiovascular and diabetes risk at lower BMI levels. Always discuss your personal thresholds with your GP.
What health risks are associated with BMI class obesity?
Obesity significantly increases the risk of type 2 diabetes, heart disease, stroke, high blood pressure, certain cancers, sleep apnoea, and joint problems. Severe obesity (Class III) carries the highest risk. However, weight loss of even 5–10% can reduce these risks and improve health markers like blood sugar and cholesterol.
How can I find out my BMI class?
Calculate your BMI using our free BMI calculator on this page—simply enter your height and weight in either metric (kg, cm) or imperial (lbs, feet/inches) measurements. The calculator will instantly show your BMI number and which NHS category you fall into, including ethnicity-adjusted thresholds if relevant.
What support does the NHS offer for BMI class obesity?
Start by speaking with your GP, who can assess your individual health and refer you to appropriate support. The NHS weight management pathway includes tier 1 self-help resources, tier 2 community programmes, and tier 3 specialist multidisciplinary services. Prescription weight loss treatment is available through specialist services for eligible patients, alongside lifestyle changes and support.
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.