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
How to Figure Out Your BMI
Figuring out your BMI is straightforward using a simple formula based on your weight and height. BMI (Body Mass Index) is a useful screening tool that helps you understand whether your weight falls within a healthy range according to NHS guidelines. In the UK, we use kilograms and metres for the calculation, though you can work with stone and pounds too. Use our free BMI calculator above to get your result instantly, or follow the formula to work it out manually. Understanding your BMI is a helpful first step in assessing your overall health and weight.
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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.
BMI Formula and Calculation Method
The BMI formula is simple: divide your weight in kilograms by your height in metres squared (kg ÷ m²). For example, if you weigh 75kg and are 1.73m tall, your calculation would be 75 ÷ (1.73 × 1.73) = 75 ÷ 2.99 = 25.1.
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial approximation: BMI = (weight in lbs × 703) ÷ height (inches)²
Once you have your number, compare it against the BMI range UK categories. The NHS defines healthy BMI as 18.5 to 24.9 for most adults. A BMI between 25 and 29.9 falls in the overweight category, while 30 and above indicates obesity. For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the NHS BMI thresholds are lower: healthy weight is 18.5 to 22.9.
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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 may have a high BMI but low body fat percentage. It also does not account for where fat is stored on your body; waist circumference is equally important for health. For this reason, your GP may assess BMI categories UK alongside other measurements like waist-to-height ratio and blood pressure. A single number never tells the complete health story. Use our free weight converter to check your measurements in different units, then discuss the results with your GP for personalised advice about what your BMI means for your individual health.
- 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 according to NHS guidelines?
The NHS defines a healthy BMI as 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. Your GP can advise what a healthy weight is for you personally.
How do I calculate BMI if I use stone and pounds?
Convert stone and pounds to kilograms first. One stone equals 6.35kg, and one pound equals 0.454kg. Then use the standard formula: weight (kg) ÷ height (m)². Our free weight converter makes this conversion instant.
What does a BMI over 30 mean?
A BMI of 30 or above falls into the obesity category according to NHS classification. This indicates increased health risks related to weight, though BMI is just one measure. Your GP can discuss your individual health and any steps to take.
Is BMI accurate for everyone?
BMI has limitations. It does not distinguish muscle from fat, so athletes may have high BMI with low body fat. It also does not account for age, bone density, or where fat is stored. Use it alongside waist measurement and other health markers.
Where can I find a BMI chart for UK adults?
The NHS provides official BMI guidance and categories. Our free BMI calculator on this page gives you your personal result instantly based on your height and weight. For children, different age-specific charts apply — always check with your GP.
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.