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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NHS Weight BMI — Understanding UK Health Categories
The NHS uses BMI (body mass index) as a screening tool to assess whether an adult's weight falls within a healthy range for their height. BMI is calculated by dividing your weight in kilograms by your height in metres squared. According to NHS guidelines, a healthy BMI sits between 18.5 and 24.9 for most UK adults, though lower thresholds apply for people of South Asian, Chinese, Black African, and Black Caribbean heritage due to higher health risks at lower BMI levels. Understanding your BMI category is a useful first step in assessing your weight-related health, though it's important to recognise that BMI has limitations.
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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 Ranges and Weight Categories
The NHS BMI formula is: weight (kg) ÷ height (m)². Using this calculation, NHS guidelines categorise adults into these BMI categories UK:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese (Class III): BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the overweight BMI threshold starts at BMI 23.0 (rather than 25.0), and obesity begins at BMI 27.5. This reflects evidence showing these populations face higher cardiovascular and metabolic risks at lower BMI levels. You can calculate your personal BMI using our free BMI calculator on this page to identify your category instantly.
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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 Complementary Health Measures
BMI limitations are important to understand: BMI does not distinguish between muscle mass and fat mass, so muscular individuals may have a high BMI despite low body fat. Conversely, people who are sedentary may have a normal BMI but carry excess body fat. The NHS therefore recommends using BMI alongside other measurements for a complete picture of health.
- Waist circumference: Increased risk for men over 94cm (37 inches); increased risk for women over 80cm (31.5 inches)
- Overall fitness and activity levels
- Medical history and existing health conditions
Your GP can provide personalised assessment and advise whether your weight poses any health risk for you individually. Use our free weight converter to check your weight across kg, stone, and pounds for NHS reference.
- 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 NHS healthy BMI range?
According to NHS guidelines, a healthy BMI is 18.5 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower: 18.5 to 22.9. If your BMI falls outside these ranges, your GP can advise whether any action is needed based on your individual health.
How do I calculate my BMI using the NHS formula?
The NHS BMI formula is: weight in kilograms ÷ (height in metres × height in metres). For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. Our free BMI calculator on this page does this instantly — just enter your weight and height.
Why do South Asian and Black African adults have different BMI thresholds?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean descent have higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS therefore recommends lower thresholds (healthy weight ends at 22.9 rather than 24.9) to flag health risk earlier and enable earlier intervention.
What are the main limitations of BMI?
BMI does not account for muscle mass, bone density, age, or where fat is stored on the body. Athletes may have high BMI but low body fat. The NHS recommends combining BMI with waist measurement, fitness level, and medical history for a fuller health picture.
What should I do if my BMI is in the overweight or obese category?
Your GP can discuss your individual health and whether weight management would be beneficial. Options range from lifestyle changes (diet and exercise) to structured weight management programmes through NHS tier 3 services. In some cases, prescription medications may be considered if you have weight-related health conditions.
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.