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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BMI for Obese and Morbidly Obese Adults in the UK
Understanding your BMI range is the first step towards better health. If you have a BMI of 30 or above, the NHS classifies this as obese, with further categories for Class II and Class III (severely obese or morbidly obese). This guide explains the NHS BMI categories for obesity, what these numbers mean for your health, and how the NHS can support you. Use our free BMI calculator above to check your personal BMI instantly and find out where you fall on the NHS scale.
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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 BMI Categories and Ranges
The NHS BMI formula divides obesity into three distinct classes, each with different health implications:
- Obese Class I (BMI 30.0–34.9): Increased risk of type 2 diabetes, heart disease, and high blood pressure
- Obese Class II (BMI 35.0–39.9): Significantly higher health risks including cardiovascular disease, stroke, and joint problems
- Severely Obese/Class III (BMI 40.0+): Morbidly obese; very high risk of serious health complications including fatty liver disease, sleep apnoea, and early mortality
These NHS BMI categories UK apply to most adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds—obesity may start at a BMI of 27.5 or above due to higher disease risk in these populations. The healthy BMI range for comparison is 18.5–24.9. Calculate your BMI range UK status using our free tool on this page.
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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.
The NHS Weight Management Pathway for Obesity
If you have a BMI in the obese range, your GP can refer you to an NHS specialist weight management service. The NHS operates a four-tier pathway: Tier 1 (self-help and digital support), Tier 2 (behaviour change programmes), Tier 3 (specialist multidisciplinary services, including prescription weight loss medications), and Tier 4 (bariatric surgery for severe cases). BMI limitations are recognised by the NHS—your GP will also assess your waist circumference and overall health. Access and waiting times vary by region, but specialist services may offer proven treatments including structured diet programmes, physical activity plans, and where clinically appropriate, prescription medications. Contact your GP to discuss your options and find out what support is available in your area.
- 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 is considered morbidly obese in the UK?
A BMI of 40 or above is classified as Class III obesity (severely obese or morbidly obese) by the NHS. At this level, health risks are very significant and may include type 2 diabetes, heart disease, stroke, sleep apnoea, and joint problems. Your GP can arrange specialist support and discuss treatment options.
Is BMI the only measure the NHS uses to assess obesity?
No. While the BMI calculator is a useful screening tool, the NHS also measures waist circumference and assesses overall health history. BMI has limitations—it doesn't distinguish between muscle and fat, and placement of fat around the waist is particularly important. Your GP will consider these factors together.
Can I access weight loss treatment through the NHS if I have a BMI of 35 or above?
Yes. Adults with a BMI of 35 or above, or 30 or above with weight-related health conditions (like type 2 diabetes or high blood pressure), may be eligible for specialist NHS weight management services. Your GP can refer you to a Tier 3 service. Availability and waiting times vary by region.
What is the difference between obese and morbidly obese?
Obese Class I (BMI 30–34.9) and Class II (BMI 35–39.9) are classified as obese. Class III (BMI 40+) is classified as severely obese or morbidly obese. Morbidly obese reflects significantly higher health risks and may qualify individuals for specialist treatment options sooner, including medication or surgery.
How quickly can I expect weight loss through the NHS?
The NHS recommends safe, sustainable weight loss of 0.5–1 kg per week. This typically requires a calorie deficit of around 500 kcal per day alongside increased physical activity. If appropriate, your GP may refer you for specialist support or prescription treatment. Track your progress with our free progress tracker to monitor your journey.
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.