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 Determine Your BMI Body Mass Index
Body mass index (BMI) is a simple measurement that helps assess whether your weight is healthy for your height. Determining your BMI is quick and straightforward — you only need your weight in kilograms and your height in metres. The NHS uses BMI as an initial screening tool to identify whether adults may be at increased health risk. Understanding your BMI range is the first step towards making informed decisions about your health. Use our free BMI calculator above to find your BMI instantly, or follow the a UK pharmacy formula below to calculate it 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.
NHS BMI Formula and Categories
The body mass index formula is the same worldwide: divide your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). For example, if you weigh 70kg and are 1.73m tall, your BMI would be approximately 23.4, which falls in the healthy weight range.
According to NHS BMI categories, the standard ranges are:
- 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)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds: a healthy BMI for these groups is 18.5–22.9, and the overweight BMI threshold begins at 23.0. This is because these populations face higher health risks from excess weight at lower BMI levels.
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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 that adults with a BMI of 25 or above discuss their weight with their GP, especially if they have other health conditions like high blood pressure, type 2 diabetes, or heart disease. Your GP can offer support, lifestyle advice, or referral to NHS weight management services depending on your individual circumstances.
It's important to understand that BMI has limitations — it doesn't distinguish between muscle and fat, and doesn't account for where fat is stored. Your GP may also consider your waist circumference and overall health picture. If you're concerned about your weight or health, contact your GP for personalised guidance. You can also use the weight converter on this page to check your weight across different units (stone, lbs, kg) and track changes over time with our free progress tracker.
- 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 the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, a healthy BMI is 18.5 to 22.9. These lower thresholds reflect higher health risks at lower BMI levels in these populations.
How do I calculate my BMI manually?
Use the formula: BMI = weight (kg) ÷ height (m)². For example, if you weigh 75kg and are 1.70m tall, divide 75 by (1.70 × 1.70) = 75 ÷ 2.89 = BMI of approximately 25.9. You can also use our free BMI calculator above for gradual improvement.
What are the main limitations of BMI?
BMI doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It doesn't account for where fat is stored (waist circumference matters too) and is less accurate for elderly people, children, or during pregnancy. Your GP can provide context beyond BMI alone.
When should I contact my GP about my BMI?
Contact your GP if your BMI is above 25, especially if you have weight-related health conditions like high blood pressure, type 2 diabetes, or heart disease. Your GP can assess your individual health risk and discuss weight management options, including NHS-based services.
Is BMI the only measure of healthy weight?
No. The NHS also considers waist circumference: men over 102cm and women over 88cm are at higher health risk. Age, ethnicity, muscle mass, and overall fitness all matter. Your GP can assess your complete health picture rather than 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.