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 Is BMI Calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. The NHS uses this simple formula to assess whether an adult falls into a healthy weight range. Understanding how BMI is calculated helps you interpret your own health status and guides conversations with your GP about weight management. While BMI has limitations, it remains the primary screening tool used across UK healthcare for assessing weight-related health risks.
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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.
The BMI Formula and NHS Categories
The BMI formula is: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.73 metres tall, your BMI would be 70 ÷ (1.73 × 1.73) = 23.4. The NHS uses this result to place you into one of five BMI categories:
- Underweight: Below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obese (Class I): 30.0 to 34.9
- Severely obese (Class III): 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — healthy weight starts at 18.5 but overweight begins at 23.0 rather than 25.0. Try our free BMI calculator above to find your instant BMI and category.
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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.
NHS Weight Management and When to Seek Help
The NHS recommends maintaining a healthy BMI of 18.5 to 24.9 to reduce the risk of weight-related health conditions including type 2 diabetes, heart disease, and certain cancers. If your BMI falls outside this range, your GP can discuss personalised options. The NHS provides a structured weight management pathway: Tier 1 includes self-help tools and community programmes; Tier 2 involves primary care support; Tier 3 offers specialist weight management services including potential prescription medication; Tier 4 covers bariatric surgery for severe obesity. Most adults are advised to lose weight gradually at around 0.5 to 1 kg per week alongside lifestyle changes. Contact your GP if you're concerned about your weight or would like support with weight loss.
- 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 does my BMI number actually mean?
Your BMI is a number that indicates where your weight falls relative to your height. The NHS uses it as a screening tool to identify whether you're in a healthy weight range. A BMI of 20 is healthier than 28, for example. However, BMI doesn't distinguish between muscle and fat — athletes may have a high BMI despite low body fat. Use our free weight converter alongside the BMI calculator to understand your weight in both metric and imperial measurements.
Is the BMI formula different for men and women?
No, the BMI formula is exactly the same for both men and women: weight (kg) ÷ height (m)². However, the NHS BMI categories are identical for all adults regardless of sex. Body fat percentage ranges do differ between men and women, but BMI itself does not vary by gender.
Why does the NHS use BMI if it has limitations?
BMI is used because it's quick, inexpensive, and a good population-level screening tool. It works well for most people and correlates with health risk in large groups. However, the NHS acknowledges that BMI doesn't account for muscle mass, bone density, or where fat is stored. Your GP may also measure waist circumference for a fuller picture of your health risk.
Can I calculate my BMI if I use stone and pounds instead of kilograms?
Yes. First convert your weight to kilograms (1 stone = 6.35 kg), then use the standard BMI formula. Our free weight converter tool lets you switch between stone, pounds, and kilograms instantly, making it easy to work with whichever units you prefer.
What should I do if my BMI shows I'm overweight?
If your BMI is 25 or above, speak with your GP. They can assess your individual health, discuss your weight-related risk factors, and suggest appropriate support. This might include lifestyle changes, referral to a weight management programme, or in some cases, prescription medication as part of a structured NHS pathway. Even a 5–10% reduction in body weight can significantly improve health markers.
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.