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 in the UK — What You Need to Know
BMI (Body Mass Index) is a standard measurement used across the UK NHS and healthcare system to assess whether an adult's weight falls into a healthy range for their height. Understanding your BMI is the first step in managing your weight and overall health. This UK health guide explains how BMI works, what the NHS categories mean, and how to interpret your personal BMI in the context of modern UK health advice. Whether you're checking your current weight status or planning lifestyle changes, knowing your BMI gives you a clear health reference point.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 classifies BMI into five main categories for UK adults:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
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 range is 18.5 to 22.9, and overweight begins at 23.0. Use our free BMI calculator above to check your personal BMI instantly and see which category applies to you.
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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 It Doesn't Tell You
While BMI is a useful screening tool recommended by the NHS, it has important limitations. BMI does not distinguish between muscle and fat — athletes and very muscular individuals may have a high BMI but low body fat. BMI also does not account for where fat is stored on your body; waist circumference is equally important for assessing health risk. Waist measurement above 94cm (37 inches) in men and 80cm (31.5 inches) in women signals increased risk. Older adults may have reduced muscle mass, making BMI less accurate. If your BMI suggests overweight or obesity, your GP can provide personalised nhs guidance and may recommend additional health checks including blood pressure and cholesterol screening.
- 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?
BMI is calculated as weight in kilograms divided by height in metres squared (kg ÷ m²). For imperial measurements, multiply weight in pounds by 703, then divide by height in inches squared. Our free BMI calculator on this page does this instantly — just enter your height and weight, and it shows your BMI and NHS category.
What's the difference between BMI and body fat percentage?
BMI measures weight relative to height only. Body fat percentage measures the actual proportion of your body weight that is fat tissue. BMI does not distinguish between muscle and fat, so a very muscular person may have a high BMI but low body fat. Both measurements together give a more complete picture of your health.
Is BMI different for men and women in the UK?
The NHS uses the same BMI categories for both men and women. However, women typically have naturally higher body fat percentages than men at the same BMI. Your GP can discuss what BMI means for your individual health based on your fitness level, muscle mass, and medical history.
Does ethnicity affect BMI interpretation in the UK?
Yes. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, and Black Caribbean heritage because these populations have higher risk of type 2 diabetes and heart disease at lower BMI levels. If you're from these backgrounds, discuss your BMI with your GP for personalised health guidance.
What should I do if my BMI shows I'm overweight or obese?
Start by speaking to your GP, who can assess your individual health and discuss options including dietary changes, physical activity, and whether weight management support might help. The NHS offers tiered weight management services. Use our free weight converter and progress tracker to monitor any changes, and remember that even a 5–clinically studied weight loss can have meaningful health benefits.
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.