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 Find Out Your BMI
Finding out your BMI is straightforward and takes just two measurements: your weight and your height. BMI (Body Mass Index) is a simple health screening tool used by the NHS to assess whether your weight falls into a healthy range. This guide explains the BMI formula, how to calculate it, and what your result means according to NHS guidelines—including how to use our free BMI calculator to get an gradual improvement.
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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 Formula and Categories
The BMI formula is: weight (kg) ÷ height (metres)². For example, if you weigh 70kg and are 1.75m tall, your BMI would be 70 ÷ (1.75)² = 22.9, which falls in the healthy weight range.
The NHS BMI categories UK are:
- Below 18.5: Underweight
- 18.5 to 24.9: Healthy weight
- 25.0 to 29.9: Overweight
- 30.0 to 34.9: Obese (Class I)
- 35.0 to 39.9: Obese (Class II)
- 40.0 and above: Severely obese (Class III)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower healthy BMI thresholds: 18.5 to 22.9 for healthy weight, as these groups have higher health risks at standard BMI levels. Use our free BMI calculator above to find your result instantly and see which category you fall into.
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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.
What the NHS Says About BMI and Weight Management
NICE (National Institute for Health and Care Excellence) and the NHS recommend BMI as an initial screening tool, though it has BMI limitations—it doesn't distinguish between muscle and fat, and doesn't account for where fat is stored. Your waist circumference also matters: the NHS advises men should aim for under 94cm (37 inches) and women under 80cm (31.5 inches) for reduced health risk.
If your BMI is 25 or above, or if you have concerns about your weight, speak to your GP. The NHS offers a tiered weight management pathway: self-help and digital tools (Tier 1), primary care programmes (Tier 2), specialist weight management services (Tier 3), and bariatric surgery (Tier 4). Your GP can assess which support is right for you and refer you to appropriate services. Converting between units? Try our weight converter to switch between kg, stone, and pounds while working out your BMI context.
- 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 the easiest way to find out my BMI?
The easiest way is to use our free BMI calculator on this page—simply enter your weight and height in either metric or imperial units, and your BMI and category will display instantly. Alternatively, use the formula: weight (kg) ÷ height (metres)². For example, 70kg ÷ (1.75)² = BMI 22.9.
Is BMI a reliable measure of health?
BMI is a useful initial screening tool and is recommended by the NHS, but it has limitations. It doesn't distinguish between muscle and fat—athletes may have a high BMI but low body fat. BMI also doesn't show where fat is stored. The NHS recommends measuring waist circumference alongside BMI for a fuller picture of health risk.
What BMI range does the NHS consider healthy?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9 for most adults. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a slightly lower healthy range of 18.5 to 22.9 due to higher health risks at standard BMI levels.
Should I worry if my BMI is above 25?
A BMI above 25 puts you in the overweight category, which the NHS identifies as a health risk threshold. However, individual health is complex. Speak to your GP about your specific situation, health conditions, and whether weight management support would be beneficial for you personally.
Where can I get help if my BMI indicates I'm overweight or obese?
Start by speaking to your GP, who can assess your health and refer you to appropriate NHS weight management support. The NHS offers a tiered pathway: self-help tools and digital programmes, primary care interventions, specialist weight management services (Tier 3), and bariatric surgery for severe cases. Your GP will determine which level is suitable for you.
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.