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
NHS BMI Guidance for UK Adults
The NHS uses BMI (body mass index) as a screening tool to assess whether your weight is healthy for your height. BMI categories help identify potential health risks, though BMI has limitations—it doesn't distinguish between muscle and fat, and ethnicity affects health risk at the same BMI level. Understanding your NHS BMI category is the first step towards better health. Use our free BMI calculator above to find your personal BMI instantly, then refer to this UK health guide to understand what your result means.
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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 Categories and Healthy Weight Ranges
The NHS defines five BMI categories for adults:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Severely obese (Class III): BMI 40.0 and above
However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher health risks at lower BMI levels. For these populations, overweight begins at BMI 23.0, and obesity at BMI 27.5. To find your healthy weight range for your height, use our weight converter alongside your BMI calculation to see both metric and imperial measurements.
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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.
Important BMI Limitations and Waist Measurement
BMI is useful for screening populations but has important limitations. It cannot distinguish between muscle mass and fat—athletes may have a high BMI but low body fat. BMI also doesn't account for where fat is stored. The NHS therefore recommends checking waist circumference alongside BMI:
- Men: over 94cm (37 inches) = increased risk; over 102cm (40 inches) = high risk
- Women: over 80cm (31.5 inches) = increased risk; over 88cm (34.5 inches) = high risk
Your GP can assess your individual health risk using both BMI and waist measurement, and discuss weight management options if needed.
- 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 healthy BMI range according to the NHS?
The NHS healthy weight BMI range is 18.5 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 due to higher health risks at lower BMI levels in these populations. Use our BMI calculator to check your personal BMI instantly.
Why does the NHS use different BMI thresholds for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean descent have higher risks of type 2 diabetes and cardiovascular disease at lower BMI levels compared to other populations. The NHS adjusted thresholds reflect this evidence to provide more accurate health risk assessment for these groups.
Is BMI accurate for muscular or athletic people?
No. BMI doesn't distinguish between muscle and fat. Athletes or very muscular individuals may have a higher BMI but actually have low body fat and good health. If you're very muscular, discuss your weight and health with your GP rather than relying on BMI alone.
Should I check my waist measurement as well as BMI?
Yes. The NHS recommends measuring waist circumference alongside BMI because where fat is stored matters for health risk. Even with a healthy BMI, excess abdominal fat can increase cardiovascular risk. Your GP can advise on healthy measurements for your individual circumstances.
What should I do if my BMI is in the overweight or obese category?
If your BMI is above 25, speak to your GP. They can assess your overall health, discuss any weight-related health conditions, and help you plan a weight management approach. This might include dietary changes, increased physical activity, or in some cases, 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.