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 is the Obese BMI Range According to NHS Guidelines?
In the UK, a BMI of 30 or above is classified as obese according to NHS guidelines. The obese category is further divided into three classes based on health risk: Class I (30–34.9), Class II (35–39.9), and Class III (40 and above, also called severe obesity). If you're unsure of your BMI, you can calculate it using our free BMI calculator above, which also shows you exactly where you fall within the NHS BMI categories. Understanding your BMI range is a useful first step in assessing your health, though it's important to remember that BMI has limitations and doesn't account for muscle mass or where fat is stored.
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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 Obesity Classification and Health Risk
The NHS BMI obesity classifications are based on health risk levels. A BMI of 30 to 34.9 is Class I obesity — associated with increased health risk. A BMI of 35 to 39.9 is Class II obesity — associated with high health risk. A BMI of 40 or above is Class III obesity (severe obesity) — associated with very high health risk.
These classifications help GPs and healthcare professionals assess whether you might benefit from weight management support. NICE guidance recommends that adults with obesity should be offered structured weight management support, which may include lifestyle interventions, behaviour change programmes, or in some cases, prescription weight loss medication.
Important context: ethnicity affects these thresholds. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. For these populations, a BMI of 27.5 or above is considered obese.
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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 Getting Help
If your BMI falls into the obese category, the NHS offers a structured pathway to support. Most people start with Tier 1 self-help resources, including free digital tools and community weight management programmes. Your GP can refer you to Tier 2 primary care interventions, which include behaviour change support and structured diet and activity programmes.
For more intensive support, Tier 3 specialist weight management services are available through NHS trusts in your area — these services can assess you for prescription weight loss medication if appropriate, including GLP-1 injections like Mounjaro or Wegovy. Track your weight loss progress alongside lifestyle changes using our free progress tracker, and remember that even a 5–10% reduction in body weight can meaningfully improve health outcomes like blood pressure and blood sugar control.
- 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 BMI number counts as obese in the UK?
According to NHS guidelines, a BMI of 30 or above is classified as obese. This is divided into Class I (30–34.9), Class II (35–39.9), and Class III or severe obesity (40+). Use our free BMI calculator to find your personal BMI instantly.
Is the obese BMI range the same for all ethnic groups?
No. The NHS recommends lower thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups face higher health risks at lower BMI levels. For these populations, BMI of 27.5 or above is considered obese.
What should I do if my BMI is in the obese range?
Start by speaking with your GP. The NHS offers a structured weight management pathway including self-help resources, behaviour change programmes, specialist services, and in some cases, prescription weight loss medication. Your GP can help you identify the right support for your situation.
Can BMI be inaccurate even if it shows obesity?
Yes. BMI doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI but low body fat. BMI also doesn't show where fat is stored. Your GP can assess your overall health beyond BMI alone, including waist circumference and blood pressure.
What are the health risks of being in the obese BMI range?
Obesity increases risk of type 2 diabetes, cardiovascular disease, high blood pressure, certain cancers, sleep apnoea, and joint problems. However, losing even 5–10% of your body weight can significantly reduce these risks and improve health markers like blood sugar and cholesterol.
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.