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
BMI Categories for Obesity Explained
Obesity is classified into three distinct categories based on your BMI (Body Mass Index), according to NHS guidelines. Understanding which category applies to you is the first step in assessing your health risk and exploring treatment options. BMI is calculated using your weight in kilograms divided by your height in metres squared. This guide explains the obesity BMI ranges, how to calculate yours, and what each category means for your health. Use our free BMI calculator above to find your personal BMI instantly.
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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 Obesity Categories and Ranges
The NHS recognises three classes of obesity, each with different health implications:
- Obese Class I: BMI 30.0 to 34.9 — increased health risks
- Obese Class II: BMI 35.0 to 39.9 — high health risks
- Severely Obese (Class III): BMI 40.0 and above — very high health risks
For comparison, healthy weight ranges from BMI 18.5 to 24.9, and overweight falls between BMI 25.0 and 29.9. However, South Asian, Chinese, Black African, and Black Caribbean adults face higher health risks at lower BMI levels — the NHS recommends lower thresholds for these groups, with obesity beginning at BMI 27.5 and above. Your GP can help interpret what your BMI means for your individual health status. Try our weight converter to see your weight in different units, or use the BMI formula: weight (kg) ÷ height (m)².
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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
BMI is a useful screening tool but has important limitations. It does not distinguish between muscle and fat — athletes and very muscular individuals may have a high BMI but low body fat percentage. BMI also ignores where fat is stored; excess weight around the stomach (waist circumference) poses greater health risks than weight distributed elsewhere. For a more complete picture, your GP may measure your waist circumference (healthy target: under 94cm for men, under 80cm for women) or assess other health markers like blood pressure and cholesterol. Weight is influenced by genetics, medical conditions, medications, and environment — BMI alone does not tell the whole story of your health.
- 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.
How do I calculate my BMI to check which obesity category I fall into?
BMI is calculated by dividing your weight in kilograms by your height in metres squared. For example, if you weigh 95kg and are 1.75m tall: 95 ÷ (1.75 × 1.75) = BMI 30.6 (Obese Class I). Our free BMI calculator above performs this instantly — simply enter your weight and height.
Are the BMI obesity categories the same for everyone in the UK?
Most UK adults use the standard NHS categories (Class I, II, III). However, the NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels. Ask your GP if adjusted thresholds apply to you.
What health risks are associated with each obesity category?
Obese Class I increases risk of type 2 diabetes and heart disease. Class II significantly raises these risks plus sleep apnoea and joint problems. Severely Obese (Class III) poses very high risks of multiple conditions. Even modest weight loss (5–10%) can improve health markers.
Can BMI be inaccurate for some people?
Yes. BMI does not account for muscle mass, so athletes and very fit individuals may have high BMI but low body fat. BMI is also less accurate for elderly people due to muscle loss, and less reliable during pregnancy. Waist circumference and other health markers provide additional context.
What should I do if my BMI falls into the obesity category?
Speak to your GP about your personal health risk. They can assess your overall health, discuss lifestyle changes, and explain treatment options if appropriate — including structured weight management programmes and, if suitable, prescription weight loss support through NHS specialist services.
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.