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
What Does BMI Mean? An NHS Health Guide
BMI stands for Body Mass Index — a measurement that uses your height and weight to assess whether you're in a healthy weight range. The NHS uses BMI as a screening tool to identify whether adults may be at risk of weight-related health conditions. While BMI has limitations, it's a practical starting point for understanding your health. Your personal BMI tells you which category you fall into according to NHS guidelines, and helps your GP assess your individual health risks. Use our free BMI calculator above to find your personal BMI instantly.
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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 What They Mean
The NHS divides adults into four main BMI categories based on their measurement. A healthy BMI is between 18.5 and 24.9 — this range is associated with lower risk of weight-related diseases. An overweight BMI threshold starts at 25.0 and goes up to 29.9, which may increase health risks. Obese ranges begin at 30.0, with Class I obesity (30–34.9), Class II (35–39.9), and severely obese (40+).
However, the NHS also recognises that for adults of South Asian, Chinese, Black African, and Black Caribbean heritage, lower thresholds apply. For these groups, a healthy BMI may be 18.5–22.9, and overweight begins at 23.0. This is because research shows these populations face higher diabetes and cardiovascular risk at lower BMI levels.
Your GP can explain what your BMI category means for your personal health and recommend next steps if needed.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
NHS Weight Management and When to Seek Help
The NHS offers a structured weight management pathway with support at different levels. If your GP identifies that your weight poses a health risk, they may refer you to tier 3 or tier 4 services — specialist weight management teams or bariatric surgery services. Many people start with free NHS resources like the NHS Weight Loss Plan or digital tools available through your local health service.
You don't need to wait for your BMI to reach a certain level to seek help — if you have concerns about your weight and health, speak to your GP. They can assess your individual situation, discuss lifestyle changes, and explain what support is available. NICE guidance supports early intervention and personalised approaches to weight management.
- 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 BMI formula used by the NHS?
The NHS BMI formula is weight in kilograms divided by height in metres squared (kg ÷ m²). For example, if you weigh 70kg and are 1.75m tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9. Use our free BMI calculator on this page to calculate yours automatically.
Why does the NHS have different BMI categories for different ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults develop weight-related diseases like type 2 diabetes at lower BMI levels than White European adults. The NHS adjusted thresholds to better identify health risk in these populations and ensure equitable care.
What are the main limitations of BMI?
BMI doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored (waist measurement matters), age-related muscle loss, or individual health variations. Your GP can assess your overall health beyond just BMI.
If my BMI is healthy, does that mean I'm healthy?
A healthy BMI is a good sign, but health involves many factors — fitness level, blood pressure, cholesterol, mental health, and lifestyle. Your GP looks at your whole picture, not just BMI. If you're concerned about your health, discuss it with your GP.
Should I use the healthy BMI range to set my weight loss goal?
Yes, the NHS healthy BMI range (18.5–24.9, or lower for some ethnic groups) is a useful reference point. However, your personal ideal weight depends on your frame size, muscle mass, and individual health. Work with your GP or a dietitian to set realistic, health-focused goals rather than aiming for a specific number.
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.