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 — it's a measurement that tells you whether your weight is healthy for your height. The NHS uses BMI as a screening tool to assess health risk, and understanding your personal BMI range is a useful starting point for health conversations with your GP. This guide explains how to calculate your BMI, what the NHS categories mean, and what to do next based on your results. You can calculate it manually using a simple formula, or use our free BMI calculator above for 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.
How to Calculate Your BMI Using the NHS Formula
Your BMI is calculated using a simple mathematical formula that compares your weight to your height. The BMI formula is: weight (kg) ÷ height (m)². To calculate manually, weigh yourself in kilograms, measure your height in metres, then square your height and divide your weight by that number. For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI. The NHS recommends this as the standard method for adults. However, the easiest way is to use our free BMI calculator on this page — enter your weight and height, and it calculates instantly. If you prefer working in stone and pounds, our weight converter can help you switch to kilograms first. The BMI range for healthy weight according to NHS guidelines is 18.5 to 24.9. BMI limitations are important to understand — BMI does not distinguish between muscle and fat, so athletes or very muscular individuals may have a higher BMI despite being healthy.
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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 BMI Categories and What Your Result Means
The NHS provides clear BMI categories UK adults should understand: a BMI below 18.5 is underweight, 18.5–24.9 is healthy weight, 25.0–29.9 is overweight, 30.0–34.9 is obese (Class I), 35.0–39.9 is obese (Class II), and 40.0 or above is severely obese. If you are of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds — your healthy range starts at 18.5 but overweight begins at 23.0 rather than 25.0. This is because these groups face higher health risks from type 2 diabetes and heart disease at the same BMI levels. NICE guidance supports using BMI as part of a broader health assessment, alongside waist measurement and other risk factors. Your GP can provide personalised advice about what your BMI means for you and whether any action is needed.
- 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.
Can I calculate my BMI without using a calculator?
Yes. Divide your weight in kilograms by your height in metres squared. For example, 70kg ÷ (1.75m × 1.75m) = 22.9 BMI. However, our free BMI calculator on this page does this instantly and is more convenient, especially if you need to convert stone and pounds to kilograms first.
What should I do if my BMI is above 25?
A BMI above 25 falls in the overweight category. This doesn't mean you need immediate action, but it's worth discussing with your GP. They can assess your overall health, check your waist circumference and other risk factors, and advise whether lifestyle changes or further support would be helpful.
Is BMI accurate for athletes or very muscular people?
No. BMI does not distinguish between muscle and fat, so athletes or individuals with significant muscle mass may have a high BMI despite low body fat. If you fall into this category, discuss your results with your GP — they can assess your health more holistically.
Why are BMI thresholds different for South Asian and Black African populations?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher health risks from obesity-related conditions at lower BMI levels. The NHS recommends adjusted thresholds for these groups to better reflect their individual risk profiles.
What is the NHS weight management pathway if my BMI is high?
The NHS offers a four-tier pathway. Tier 1 includes self-help and community programmes. Your GP can refer you to Tier 2 for behaviour change support. Tier 3 involves specialist weight management services where medication may be considered. Tier 4 is bariatric surgery for severe obesity. Availability varies by region — ask your GP about local services.
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.