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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What Does Your BMI Level Mean? NHS Guide
Your BMI (body mass index) is a measurement that helps assess whether you're at a healthy weight for your height. The NHS uses standardised BMI categories to guide health decisions, and understanding where your level sits is an important first step in health management. This guide explains the official NHS BMI ranges, what each category means for your health, and when to contact your GP for personalised advice. Use our free BMI calculator above to find your personal BMI instantly, and see where you fall on the NHS scale.
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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 What They Mean
The NHS and NICE (National Institute for Health and Care Excellence) use standardised BMI categories to classify adults into health levels. These ranges apply to most UK adults aged 18 and over:
- BMI below 18.5 = Underweight
- BMI 18.5 to 24.9 = Healthy weight (the recommended healthy BMI range
- BMI 25.0 to 29.9 = Overweight
- BMI 30.0 to 34.9 = Obese (Class I)
- BMI 35.0 to 39.9 = Obese (Class II)
- BMI 40.0 and above = Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher health risks at the same BMI level. For these populations, a healthy BMI level sits between 18.5 and 22.9, and overweight begins at 23.0. Calculate your personal BMI using the calculator on this page to identify your specific category and understand what it 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 Pathways and Next Steps
Once you know your BMI level, the NHS offers a structured approach to weight management. If your BMI puts you in the overweight or obese categories, your GP can discuss your individual health picture—including family history, blood pressure, and other factors—to determine next steps. The NHS weight management pathway includes tier 1 self-help resources and digital tools (like the weight converter and BMI calculator on this site), tier 2 programmes led by your practice, tier 3 specialist weight management services, and tier 4 bariatric surgery for eligible patients with severe obesity and significant health complications.
Many people benefit from gradual lifestyle changes supported by their GP. If prescription weight loss treatment may be appropriate for your BMI level and health circumstances, your GP can refer you to a specialist tier 3 service for assessment.
- 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 level is considered healthy according to the NHS?
The NHS defines a healthy BMI as between 18.5 and 24.9 for most UK adults. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9. These ranges are based on research showing health risks increase outside these levels. Use the BMI calculator on this page to find your personal healthy weight range for your height.
What does it mean if my BMI level is in the overweight category?
A BMI level between 25.0 and 29.9 means you're classified as overweight according to NHS guidelines. This doesn't necessarily mean immediate health danger, but it suggests your health risks are higher than those in the healthy BMI range. Your GP can assess your overall health picture and discuss whether lifestyle changes or further support would be helpful.
Why are BMI thresholds different for some ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults develop weight-related health conditions (like type 2 diabetes and heart disease) at lower BMI levels than white European populations. The NHS therefore recommends lower BMI thresholds for these groups to identify health risk earlier and enable earlier intervention.
What are the limitations of using BMI level as a health measure?
BMI doesn't distinguish between muscle and fat—athletic individuals may have a high BMI but low body fat. It doesn't account for where fat is stored on your body, which matters for health risk. BMI is also less accurate for elderly people, pregnant women, and very tall or short individuals. Your GP can discuss BMI alongside other measurements like waist circumference.
When should I contact my GP about my BMI level?
If your BMI level is outside the healthy range (below 18.5 or above 25.0), it's worth discussing with your GP, especially if you have weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can give personalised advice based on your complete health picture and discuss support options if needed.
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.