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 Categories for Obesity — NHS UK Health Guide
Understanding BMI categories for obesity helps you assess your health status according to NHS guidelines. In the UK, obesity is defined by specific BMI ranges, with categories ranging from Class I to Class III based on severity. This guide explains what each obesity BMI category means, how the NHS uses these classifications, and when you might benefit from seeking support from your GP or NHS weight management services.
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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 Classifications
The NHS uses standardised BMI ranges to classify weight status in UK adults. According to NHS guidance, obesity begins at a BMI of 30.0 kg/m² and above. The bmi formula is: weight in kg ÷ (height in metres)².
- BMI 30.0–34.9: Obese (Class I)
- BMI 35.0–39.9: Obese (Class II)
- BMI 40.0+: Severely obese (Class III)
These classifications help GPs and healthcare professionals assess health risk. People with a healthy BMI range between 18.5 and 24.9 have lower risk of weight-related conditions. A bmi range uk for overweight is 25.0–29.9, which sits between healthy and obese categories. Important note: BMI has bmi limitations — it does not distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. Your GP can discuss what your personal BMI means for your health.
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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 an obesity category, the NHS offers support through a structured weight management pathway. Most people start at Tier 1 with self-help tools and community programmes. If you have weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea, your GP may refer you to specialist Tier 3 services. These services can provide dietary advice, behaviour change support, and in some cases, prescription weight loss medication following clinical assessment. Use our free BMI calculator above to check your personal BMI, and if you have concerns, arrange an appointment with your GP who can discuss your individual options and any underlying health factors.
- 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 obese Class I, II, and III?
Class I obesity (BMI 30–34.9) carries moderate health risk. Class II (BMI 35–39.9) carries higher risk. Class III or severe obesity (BMI 40+) carries the highest health risk and typically qualifies for NHS specialist support and possible medication or bariatric surgery consideration.
Is BMI the only measure of health the NHS uses?
No. The NHS also considers waist circumference, blood pressure, blood glucose, and cholesterol. Waist measurement above 94cm in men or 80cm in women indicates increased health risk. Your GP will assess all these factors together, not BMI alone.
Can I have a high BMI but still be healthy?
Some people with higher BMI (such as athletes with significant muscle mass) may have low body fat and good cardiovascular health. However, BMI remains a useful screening tool. Your GP can assess your individual health through blood tests, fitness, and other markers to give you a complete picture.
Does my ethnicity affect what BMI range is healthy for me?
Yes. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, or Black Caribbean heritage. For these groups, a healthy BMI is 18.5–22.9 (not 18.5–24.9), as they face higher risk of type 2 diabetes and heart disease at lower BMI levels.
What should I do if my BMI falls into obesity?
Book an appointment with your GP. They can discuss your personal health, assess any weight-related conditions, and refer you to NHS weight management services if appropriate. You can also use our free BMI calculator to track progress and explore evidence-based lifestyle changes with your healthcare team.
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.