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 Calculate Your Body BMI
Body mass index (BMI) is a simple calculation that estimates whether your weight is healthy for your height. The BMI formula uses your weight in kilograms divided by your height in metres squared. It's one of the tools the NHS uses to assess whether you're at a healthy weight, though it has important limitations. Our free BMI calculator above will work out your score instantly, but understanding how the calculation works helps you interpret your result accurately.
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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 How to Calculate It
The BMI formula is: weight (kg) ÷ height (m)²
To calculate manually: measure your height in metres (convert cm by dividing by 100), then square that number. Divide your weight in kilograms by this squared height value. For example, if you weigh 70kg and are 1.73m tall: 70 ÷ (1.73 × 1.73) = 70 ÷ 2.99 = 23.4 BMI.
Once you have your BMI number, compare it against the NHS BMI categories UK:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight
- 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)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds—a healthy BMI range of 18.5–22.9, and overweight starts at 23.0. Use our free BMI calculator on this page to check your personal score instantly against the correct category for your ethnicity.
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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.
Understanding BMI Limitations and What Else Matters
While the bmi formula is widely used, it has significant limitations. BMI doesn't distinguish between muscle and fat—athletes or very fit people may have a high BMI but low body fat. It also doesn't account for where fat is stored; excess fat around the stomach poses greater health risk than fat elsewhere, which is why the NHS also measures waist circumference. For older adults, pregnant women, and people with disabilities, BMI may be less accurate.
Use your BMI as one screening tool alongside other measures: your overweight bmi threshold is just a starting point. A GP can assess your individual health risk. Track your progress over time using our free progress tracker, and remember that sustainable health involves diet, physical activity, and overall wellbeing—not just a number.
- 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 for adults in the UK?
According to NHS guidelines, a healthy BMI range is 18.5 to 24.9. For South Asian, Chinese, Black African, and Black Caribbean adults, the NHS recommends a slightly lower healthy range of 18.5 to 22.9, as these groups face higher health risks at higher BMI levels. Use our free BMI calculator to check whether your weight falls in the healthy range for your height.
Can I calculate BMI using stone and pounds instead of kilograms?
The NHS BMI formula uses metric units (kg and metres). If you know your weight in stone and pounds, use our free weight converter on this page to convert to kilograms first, then use the BMI calculator. Alternatively, use the approximate imperial formula: (weight in lbs × 703) ÷ height (inches)².
Why does BMI not account for muscle mass?
BMI only measures total weight relative to height—it cannot distinguish between muscle, fat, bone, and water. Someone who is very muscular may have a high BMI despite low body fat. This is why the NHS recommends checking waist circumference too, and why consulting your GP provides a more complete picture of your health.
What should I do if my BMI falls in the overweight or obese category?
Speak with your GP about your individual health risk. They can discuss lifestyle changes like diet and exercise, assess whether prescription support might help, and check for weight-related health conditions. Even a 5–10% reduction in body weight can bring meaningful health benefits. Our free progress tracker can help you log changes over time.
Is BMI the only measure of healthy weight?
No. The NHS uses BMI alongside waist circumference, blood pressure, and blood tests to assess overall health risk. Other useful measures include body fat percentage and waist-to-height ratio. Always consult your GP for personalised health advice rather than relying on BMI alone. ```
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.