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 Weight
Checking your BMI weight is straightforward and takes just two pieces of information: your weight and your height. BMI (body mass index) is a simple screening tool used by the NHS and healthcare professionals across the UK to assess whether you're at a healthy weight. In this guide, we'll show you exactly how to check your BMI weight, explain what the different BMI ranges mean, and help you understand whether your result falls into the healthy, overweight, or obese category according to NHS guidelines. You can calculate your BMI instantly using our free BMI calculator above, or learn the formula to work it out 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.
How to Calculate Your BMI Using the NHS Formula
The BMI formula is simple and works the same way for all adults in the UK. You divide your weight in kilograms by your height in metres squared. The equation is: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75 metres tall, your calculation would be: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI.
Once you have your BMI number, you can check it against the NHS BMI categories UK to see which range you fall into. Our free BMI calculator above does this automatically — simply enter your weight in kilograms (or stone and pounds if that's easier) and your height in centimetres or feet and inches, and your exact BMI will be calculated instantly. This saves you doing the maths yourself and gives you an immediate result.
- Healthy BMI range: 18.5 to 24.9
- Overweight BMI threshold: 25.0 to 29.9
- Obese (Class I): 30.0 to 34.9
- Obese (Class II): 35.0 to 39.9
- Severely obese (Class III): 40.0 and 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.
Important Limitations and Complementary Measures
While BMI is a useful initial screening tool, it has important BMI limitations that are worth understanding. BMI does not distinguish between muscle and fat — so athletes or very muscular individuals may have a high BMI but actually be very fit with low body fat. It also doesn't account for where fat is stored on your body, which matters for health risk.
The NHS recommends checking your waist circumference alongside your BMI for a fuller picture. Men should aim for a waist under 94cm (37 inches), and women under 80cm (31.5 inches). If you're of South Asian, Chinese, Black African, or Black Caribbean descent, NHS thresholds are slightly lower. Your GP can provide personalised advice about what your BMI means for your individual health, especially if you have existing health conditions.
- 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 a healthy BMI weight according to the NHS?
A healthy BMI weight falls between 18.5 and 24.9 according to NHS guidelines. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a healthy BMI range of 18.5 to 22.9, as these groups face higher health risks at slightly higher BMI levels. Your GP can advise what's healthy for you personally.
How do I check my BMI weight if I only know my weight in stone?
You can convert stone to kilograms first (multiply stone by 6.35), then use the BMI formula. Alternatively, our free BMI calculator accepts stone and pounds directly — just enter your weight and height in whatever units you prefer, and it will calculate your BMI instantly.
Is BMI weight the only measure of healthy weight I should use?
No. BMI is a useful screening tool but doesn't account for muscle mass or fat distribution. The NHS also recommends checking your waist circumference. Men should aim for under 94cm, women under 80cm. Combined with BMI, this gives a better picture of your health risk. Your GP can provide personalised guidance.
What if my BMI weight falls in the overweight category?
An overweight BMI (25.0 to 29.9) means you may benefit from making lifestyle changes like increasing physical activity and reviewing your diet. However, your GP can assess your individual health and whether intervention is needed, especially if you have other health conditions like high blood pressure or diabetes.
Can I use BMI to check my child's weight?
No. Children's BMI uses age and sex-specific charts, not the adult formula. If you're concerned about your child's weight, speak to your GP or health visitor. The NHS offers a free Healthy Weight Calculator specifically for children that uses the correct growth reference charts.
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.