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 Index Classification Explained
The body mass index (BMI) is a simple measurement that classifies your weight status using a formula based on your height and weight. In the UK, the NHS uses standardised BMI ranges to categorise adults into healthy weight, overweight, or obese categories. Understanding your BMI index classification helps you assess whether your weight falls within a healthy range for your height and identify any potential health risks. Your BMI is calculated once using the same formula for everyone, but the categories that define what's "healthy" vary slightly depending on your ethnic background.
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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 Index Classifications and Ranges
The body mass index (BMI) formula is straightforward: weight in kilograms divided by height in metres squared. This calculation produces a single number that the NHS uses to classify your weight status. The standard NHS BMI categories are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese class I (30.0–34.9), obese class II (35.0–39.9), and severely obese (40.0+).
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy BMI threshold is lower because these groups face higher cardiovascular and diabetes risk at the same BMI. For these populations, healthy weight is 18.5–22.9, overweight begins at 23.0, and obesity starts at 27.5. Use our free BMI calculator above to find your personal classification instantly and see exactly where you fall on the NHS scale.
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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 They Don't Tell You
While BMI classification is useful for population screening, it has important BMI limitations. BMI does not distinguish between muscle and fat—athletes and very muscular individuals may have a high BMI despite low body fat. BMI also ignores where fat is stored (abdominal fat carries higher health risk), doesn't account for age-related muscle loss, and may be less accurate during pregnancy. For a more complete picture of your health, your GP may also consider your waist circumference (above 94cm for men or 80cm for women indicates increased health risk) and overall fitness level alongside your BMI classification.
- 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 does a BMI of 25 mean according to NHS classification?
A BMI of 25 falls into the overweight category according to NHS guidelines. The overweight range is 25.0–29.9. This doesn't automatically mean you have health problems, but it suggests discussing lifestyle changes with your GP. Use the weight converter on this page to see what your current weight means in stone and kg.
Is BMI classification different for men and women?
No. The same BMI ranges and categories apply to both men and women in NHS classification. However, healthy weight ranges can differ slightly because men and women typically have different average heights. A BMI calculator accounts for individual height automatically.
Why is the healthy BMI threshold lower for South Asian adults?
Research shows South Asian, Chinese, Black African, and Black Caribbean populations have higher risk of type 2 diabetes and heart disease at lower BMI levels compared to European populations. The NHS therefore recommends a healthy BMI range of 18.5–22.9 for these groups rather than 18.5–24.9.
Can I have a high BMI and still be healthy?
Possibly. BMI is a screening tool, not a diagnostic one. Muscular athletes may have high BMI with low body fat. However, if your BMI is elevated, your GP should assess other factors like waist circumference, fitness level, blood pressure, and family history to determine your actual health risk.
What should I do if my BMI classification shows I'm overweight?
Start by speaking to your GP, who can assess your individual health. They may recommend gradual lifestyle changes like increasing physical activity and adjusting your diet. The NHS recommends losing weight at 0.5–1kg per week. Track progress with our free progress tracker tool.
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.