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? A Complete Guide to NHS Categories
BMI stands for Body Mass Index — a simple measurement that uses your weight and height to screen for weight-related health risks. The NHS uses BMI as a standard health screening tool to help identify whether adults fall into a healthy weight range. However, BMI is just one part of assessing overall health; it doesn't measure body fat directly or account for muscle mass. Understanding what your BMI means and how the NHS interprets it helps you make informed decisions about your health. Use our free BMI calculator above to find your personal BMI instantly, and then compare it against the NHS categories explained below.
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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 BMI formula is straightforward: weight (kg) ÷ height (m)². The result places you into one of five NHS BMI categories:
- Underweight: BMI below 18.5 — may indicate insufficient weight for optimal health
- Healthy weight: BMI 18.5–24.9 — associated with lower health risks
- Overweight: BMI 25.0–29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0–34.9 — higher health risks
- Severely obese (Class III): BMI 40.0+ — significantly elevated health risks
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends using lower healthy bmi thresholds: 18.5–22.9 for healthy weight and 23.0–27.4 for overweight. These adjusted categories reflect higher cardiovascular and diabetes risks at lower BMI levels in these populations.
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.
BMI Limitations and When to Seek NHS Support
BMI limitations are important to understand: BMI doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. It also ignores where fat is stored — waist circumference matters for health risk. If your BMI suggests overweight or obese categories, your GP can assess your overall health picture, including family history, blood pressure, and lifestyle.
The NHS offers a structured weight management pathway. Tier 1 includes self-help and digital tools (like our free BMI calculator and progress tracker). Tier 2 involves GP-led behaviour change support. Tier 3 is specialist weight management services, where prescription options may be discussed. Contact your GP if you'd like a personalised health assessment.
- 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 BMI stand for?
BMI stands for Body Mass Index. It's a screening tool that calculates the ratio of your weight to your height squared (weight in kg ÷ height in metres²). The NHS uses it to identify whether you fall into a healthy weight range and assess health risk categories.
Is BMI accurate for everyone?
BMI has limitations. It doesn't account for muscle mass, bone density, or where fat is stored on your body. Athletes may have high BMI despite low body fat. For a complete health picture, your GP may also measure waist circumference and assess other health factors.
What's the difference between overweight and obese on the NHS scale?
According to NHS categories, overweight is BMI 25.0–29.9, while obese starts at BMI 30.0. Obese is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+). Each category indicates increasing health risks, but individual health depends on many factors beyond BMI.
Should I use different BMI categories if I'm from a South Asian background?
Yes. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage. For these groups, healthy weight is BMI 18.5–22.9 (not 24.9) because they face higher diabetes and heart disease risks at lower BMI levels.
What should I do if my BMI shows I'm overweight?
Contact your GP for a health assessment. They can discuss your individual circumstances, family history, and lifestyle. The NHS offers weight management support through its structured pathway — from self-help tools and digital programmes to specialist services. Calculate your BMI using our free tool, then book a GP appointment to discuss next steps.
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.