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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Understanding the BMI Scale in the UK
The BMI scale is the standard measurement tool used by the NHS to assess whether an adult's weight is healthy for their height. Your BMI (body mass index) is calculated by dividing your weight in kilograms by your height in metres squared. In the UK, the NHS uses specific BMI categories to help identify health risks and guide weight management decisions. Understanding where you fall on the BMI scale is an important first step towards managing your health, though it's worth knowing that BMI has limitations and should always be considered alongside other health factors like waist measurement and overall fitness.
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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 BMI scale divides adults into five main categories based on their BMI number. A healthy BMI according to NHS guidance is between 18.5 and 24.9. If your BMI falls between 25.0 and 29.9, you're classified as overweight. A BMI of 30.0 to 34.9 is classed as obese (Class I), 35.0 to 39.9 as obese (Class II), and 40.0 and above as severely obese (Class III).
It's important to note that ethnicity affects health risk at different BMI levels. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds. For these groups, a healthy BMI range is 18.5 to 22.9, and overweight begins at 23.0. This difference exists because research shows these populations face higher risks of type 2 diabetes and heart disease at lower BMI levels than white European populations.
You can check your personal BMI instantly using our free BMI calculator above, which will also show you where you fall on the NHS scale and what this means for your health context.
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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.
When to Seek NHS Support for Weight Management
If your BMI suggests you're overweight or obese, the NHS offers support through its structured weight management pathway. Many GP surgeries offer free weight management services at tier 1 level, including digital tools and community programmes. Your GP can discuss lifestyle changes, monitor your health, and refer you to specialist services if needed.
NICE (National Institute for Health and Care Excellence) recommends that adults with a BMI of 30 or above, or 25 or above with weight-related health conditions, should be offered structured weight loss support. Your GP can assess whether prescription weight loss treatment might be appropriate for you, though NHS access to medications varies by region. You can also use our free weight converter and progress tracker to monitor your weight 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 the healthy BMI range according to the NHS?
The NHS considers a BMI of 18.5 to 24.9 healthy for most UK adults. However, 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. Your GP can advise on what's healthy for you personally.
How do I calculate my BMI on the NHS scale?
BMI is calculated by dividing your weight in kilograms by your height in metres squared (kg ÷ m²). For example, if you weigh 70kg and are 1.75m tall, your BMI is 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy range. Our free BMI calculator above does this instantly for you.
What does it mean if my BMI is over 30?
A BMI of 30 or above is classed as obese by the NHS and may increase your risk of type 2 diabetes, heart disease, and certain cancers. However, BMI doesn't account for muscle mass or where fat is stored, so your GP should assess your overall health picture. The NHS recommends discussing weight management options with your GP.
Why do different ethnic groups have different BMI thresholds on the NHS scale?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage develop weight-related health problems like type 2 diabetes at lower BMI levels than white Europeans. The NHS therefore recommends lower BMI thresholds (18.5–22.9 for healthy weight) for these groups to better identify health risks early.
What are the limitations of the BMI scale?
BMI doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. It also doesn't account for age, gender, where fat is stored, or individual health factors. The NHS uses BMI as a screening tool alongside waist measurement and overall health assessment, not as a definitive diagnosis.
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.