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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How to Check Your BMI in the UK
Checking your BMI is a straightforward way to assess whether your weight is healthy for your height according to NHS guidelines. BMI (Body Mass Index) is calculated using your weight and height, and the result falls into categories that help you understand your health status. In the UK, we use specific BMI ranges aligned with NHS recommendations, and understanding your personal BMI can be the first step towards better health. You can check your BMI instantly using our free BMI calculator above, or read on to learn how to calculate it yourself.
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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 Your Result Means
The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. For example, if you weigh 70kg and are 1.73m tall, your BMI would be 70 ÷ (1.73 × 1.73) = 23.4, which falls in the healthy BMI range.
According to NHS BMI guidelines, the standard categories are:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight (target range)
- 25.0–29.9: Overweight
- 30.0–34.9: Obese (Class I)
- 35.0–39.9: Obese (Class II)
- 40.0+: Severely obese (Class III)
However, if you are of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI categories UK start lower—healthy weight is 18.5–22.9, and the overweight BMI threshold begins at 23.0 rather than 25.0. This reflects higher health risks for these groups at lower weights.
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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 to Check
While BMI limitations are important to understand, BMI remains a useful screening tool. It does not distinguish between muscle and fat—an athlete with high muscle mass may have a high BMI but low body fat. BMI also does not account for where fat is stored; abdominal fat poses greater health risks than fat stored elsewhere.
For a fuller picture, combine your BMI with waist circumference. Men should aim for under 94cm (37in), and women under 80cm (31.5in). You can also use our free weight converter to check your weight in stone if you prefer UK measurements, and our BMI calculator will give you both your BMI number and your healthy weight range instantly.
- 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.
How do I check my BMI if I'm overweight?
Use our free BMI calculator above—enter your height and weight, and it will instantly show your BMI category according to NHS guidelines. If your result falls in the overweight or obese range, your GP can offer support and discuss weight management options with you, which may include lifestyle changes or, in some cases, prescription support.
What is a healthy BMI according to NHS standards?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9 for most adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5–22.9. Your GP can advise on what a healthy weight means for your individual circumstances.
Can I use the BMI calculator if I'm very tall or very short?
Yes, the BMI formula works for all adults regardless of height. However, BMI is less accurate for people who are exceptionally tall or short, or those with high muscle mass. Your GP can provide personalised guidance on healthy weight for your body type.
Does BMI tell me everything about my health?
No—BMI is a screening tool only. It doesn't account for muscle mass, bone density, or where fat is stored. Waist circumference, fitness level, and blood pressure are also important. Your GP can assess your overall health picture beyond just your BMI number.
What should I do if my BMI shows I'm overweight or obese?
Start by discussing it with your GP, who can assess your health and discuss options. These may include dietary changes, increased physical activity, or referral to a weight management programme. Track your progress with our free progress tracker, and use our weight converter and BMI calculator regularly to monitor changes.
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.