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 do BMI scores mean? Your complete UK guide
BMI scores tell you whether your weight is healthy for your height. Your BMI number falls into different categories that help your GP assess health risk. In the UK, we use the NHS BMI formula and categories, which vary slightly for adults of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights. Understanding your personal BMI score is a useful starting point for health conversations, though it's not the whole picture. Use our free BMI calculator above to find your score instantly, then read on to understand what it means.
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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 your score means
Your BMI score is calculated by dividing your weight in kilograms by your height in metres squared. The result is a number that falls into an NHS category. For most UK adults, the healthy BMI range is 18.5 to 24.9. A BMI score below 18.5 indicates underweight status; 25.0 to 29.9 is overweight; 30.0 to 34.9 is obese (Class I); 35.0 to 39.9 is obese (Class II); and 40.0 and above is severely obese (Class III).
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends different thresholds. The healthy BMI range for these groups starts at 18.5 but ends at 22.9, with overweight beginning at 23.0 and obesity at 27.5. This reflects research showing these populations face higher risk of type 2 diabetes and heart disease at lower BMI levels.
Your individual BMI score helps your GP identify whether you're in a higher-risk category and whether lifestyle changes, medical support, or further assessment might be beneficial 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.
BMI limitations and what else matters for health
While BMI is a useful screening tool, it has important limitations. Your BMI score doesn't distinguish between muscle and fat — athletes and very fit people may have high BMI but low body fat percentage. BMI also ignores where fat is stored; excess fat around the stomach carries greater health risk than fat elsewhere. Waist circumference is equally important: for men, over 94cm (37 inches) indicates increased risk, and over 102cm (40 inches) indicates high risk. For women, increased risk starts at 80cm (31.5 inches) and high risk at 88cm (34.5 inches).
For a complete health picture, combine your BMI score with waist measurement and discuss any concerns with your GP. Try the weight converter on this page to check your weight in different units, and our free progress tracker to monitor changes over time.
- 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 a good BMI score in the UK?
According to NHS guidelines, a healthy BMI score for most UK adults is between 18.5 and 24.9. For South Asian, Chinese, Black African, or Black Caribbean adults, the healthy range is 18.5 to 22.9. Your GP can discuss whether your personal BMI score indicates any health risks.
Is BMI the same for men and women?
The BMI formula and NHS categories are identical for men and women. However, body fat percentage norms differ between sexes, and women typically have slightly higher healthy body fat percentages. Your BMI score itself is calculated the same way regardless of sex.
Why do BMI categories differ for some ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations face higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS recommends lower BMI thresholds for these groups to identify health risks earlier and enable earlier intervention.
Can BMI be inaccurate?
Yes. BMI doesn't account for muscle mass, so athletes may have high BMI but low body fat. It also ignores where fat is stored and doesn't apply to children, pregnant women, or very elderly people. Always discuss your BMI score with your GP for personalised health advice.
What's the difference between BMI and body fat percentage?
BMI is a simple weight-to-height ratio; body fat percentage measures actual fat mass. Someone with high muscle mass may have high BMI but healthy body fat. Body fat percentage is more precise but requires specialist equipment to measure accurately.
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.