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 Calculate Your BMI — Step by Step
BMI (Body Mass Index) is a simple health measure that compares your weight to your height. Calculating your BMI takes just seconds and gives you an instant insight into whether you're in a healthy weight range according to NHS guidelines. In the UK, we typically use kilograms and metres to work out BMI, though the calculation works the same way regardless of the units you prefer. Understanding your BMI is a useful first step in assessing your overall health, though it's important to remember that BMI is a screening tool only — not a complete picture of your fitness or health status.
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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 How to Calculate It
The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. Mathematically, that's BMI = weight (kg) ÷ height (m)². Here's how to work it out step by step:
- Measure your height in centimetres and convert to metres (divide by 100)
- Square your height in metres (multiply it by itself)
- Divide your weight in kilograms by this squared number
For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = BMI of 22.9. Once you have your BMI number, compare it to the NHS BMI range UK categories to see where you fall. Our free BMI calculator on this page does all this maths instantly — simply enter your weight and height and you'll see your BMI result immediately, along with which healthy BMI category you're in.
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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 Number Means
The NHS BMI categories are clear and straightforward. A BMI below 18.5 is classified as underweight, 18.5 to 24.9 is healthy weight, 25.0 to 29.9 is overweight, and 30.0 and above is obese (further subdivided into Class I, II, and III). If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the overweight BMI threshold is lower — starting at 23.0 rather than 25.0 — because these groups face higher health risks at lower BMI levels. Your GP can discuss what your individual BMI means for your health and whether any action is needed. Remember that BMI is one screening tool among many; your waist measurement, fitness level, and overall health picture matter too.
- 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 BMI stand for?
BMI stands for Body Mass Index. It's a measure of body fat based on height and weight that applies to adult men and women. The NHS uses BMI as a screening tool to help identify weight-related health risks.
Can I calculate BMI in stone and pounds?
Yes. The BMI formula works in any units. If using pounds and inches: BMI = (weight in lbs × 703) ÷ height (inches)². However, our free BMI calculator above works instantly with kg, stone, or pounds — just enter your measurement and get your result.
Is a BMI of 25 overweight?
Yes. According to NHS guidelines, a BMI of 25.0 to 29.9 is classified as overweight. However, if you're of South Asian or Black African heritage, the threshold is lower — BMI of 23.0 and above is considered overweight for these groups.
What are the BMI limitations I should know about?
BMI doesn't distinguish between muscle and fat, so athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored or changes with age. Waist circumference and overall fitness are equally important health indicators alongside your BMI.
Is a healthy BMI range the same for everyone?
The healthy BMI range of 18.5 to 24.9 applies to most adults, but people of South Asian, Chinese, and Black African or Caribbean descent have lower thresholds due to higher health risks at the same BMI. Your GP can advise on what's healthy for you personally.
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.