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
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How To Find Your BMI Index — NHS Guidance
Finding your body mass index (BMI) is a straightforward way to check whether your weight falls within a healthy range according to NHS guidelines. Your BMI is calculated using your height and weight, and it helps identify potential health risks. Whether you want to calculate it manually or use a quick online tool, this guide explains the BMI formula, NHS categories, and what your result means for your health. Use our free BMI calculator above to find your BMI instantly, or follow the steps 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.
How To Calculate Your BMI Using The NHS Formula
The body mass index formula is simple: divide your weight in kilograms by your height in metres squared. Mathematically: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your calculation would be: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI.
To calculate manually: measure your height in centimetres and convert to metres (divide by 100), then square that number. Divide your weight in kilograms by this result. The NHS uses metric measurements (kg and metres), though many UK adults prefer to think in stone and pounds — use our free weight converter to switch between units easily.
- Write down your exact weight in kg
- Measure your height in cm, then divide by 100 to get metres
- Multiply your height in metres by itself
- Divide weight by this squared height figure
- Your result is your BMI
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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 They Mean
According to NHS guidance, BMI categories fall into five groups: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese (30.0–34.9), and severely obese (40.0+). A healthy BMI range of 18.5 to 24.9 is recommended for most UK adults, though the NHS recognises that people of South Asian, Chinese, Black African, and Black Caribbean heritage have a higher risk of health complications at lower BMI levels.
If your BMI falls outside the healthy range, your GP can discuss what this means for your individual health and what steps might help. The NHS weight management pathway offers support at different levels — from free digital tools and community programmes to specialist services if 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.
What does a BMI of 25 mean according to NHS guidelines?
A BMI of 25 falls in the overweight category (25.0–29.9) according to NHS standards. While not obese, this indicates your weight is above the healthy range for your height. Your GP can advise whether lifestyle changes or further assessment is needed based on your individual health.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat — athletes may have high BMI but low body fat. BMI also doesn't account for where fat is stored or age-related muscle loss. Your GP can assess whether BMI is appropriate for your individual situation.
What's the difference between overweight and obese BMI?
Overweight BMI is 25.0–29.9, while obese is 30.0+. The distinction matters because obesity carries higher health risks including type 2 diabetes, heart disease, and certain cancers. The NHS uses these categories to guide weight management support and intervention thresholds.
Do I need to see my GP if my BMI is above 25?
Not necessarily. If you're generally healthy, your GP may suggest lifestyle changes first. However, if you have weight-related health conditions (diabetes, high blood pressure, sleep apnoea), your GP may recommend support. Use our free BMI calculator to check your BMI, then discuss any concerns with your GP.
Are NHS BMI categories different for South Asian adults?
Yes. The NHS recommends lower thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups have higher risk of type 2 diabetes and heart disease at lower BMI levels. Healthy BMI for these groups is 18.5–22.9, and overweight starts at 23.0. Discuss your individual thresholds with your GP.
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.