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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What Are BMI Classes?
BMI classes are health categories 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. The result falls into one of five main classes that indicate whether you're underweight, healthy weight, overweight, or obese. Understanding your BMI class is a useful starting point for evaluating health risk, though it's important to note that BMI has limitations and is best used alongside other health measures.
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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 Classes and Healthy Weight Ranges
The NHS BMI formula uses your weight and height to assign you to a health category. Here are the five main BMI categories UK adults fall into:
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5 to 24.9 — associated with lower health risks
- Overweight: BMI 25.0 to 29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0 to 34.9 — significantly increased health risks
- Obese (Class II): BMI 35.0 to 39.9 — very high health risks
- Severely obese (Class III): BMI 40.0 and above — severe health risks
The healthy bmi range for most adults is 18.5 to 24.9. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: a healthy BMI range starts at 18.5 but ends at 22.9, with overweight starting at 23.0. You can calculate your personal BMI instantly using our free BMI calculator above.
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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 Else Matters
BMI limitations are important to understand. BMI does not distinguish between muscle and fat — athletes or people with high muscle mass may have a high BMI but low body fat. BMI also does not account for where fat is stored, which matters for health risk. Additionally, BMI is less accurate for elderly people due to natural muscle loss, and it doesn't apply to children or pregnant women.
The NHS recommends measuring waist circumference alongside BMI for a fuller picture. Men should aim for a waist under 94cm (37 inches); women under 80cm (31.5 inches). Use our free weight converter to check your weight in different units, and speak to your GP if you have concerns about your health or weight.
- 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 formula for calculating BMI?
BMI is calculated by dividing your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). For example, if you weigh 70kg and are 1.75m tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy weight range.
What is a normal BMI range according to the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. For adults 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.
At what BMI is someone considered overweight?
The overweight BMI threshold according to NHS guidelines is 25.0 to 29.9. A BMI of 25.0 or above indicates increased risk of weight-related health conditions, though individual health depends on many factors beyond BMI alone.
Why are BMI classes different for different ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage face higher risks of type 2 diabetes and heart disease at lower BMI levels. The NHS therefore recommends lower BMI thresholds for these groups to better reflect actual health risk.
What should I do if my BMI falls in the overweight or obese category?
If your BMI indicates overweight or obesity, speak with your GP who can assess your individual health, discuss any weight-related health conditions, and suggest appropriate next steps. These might include lifestyle changes, referral to a weight management service, or other support tailored to your needs.
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.