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 Do You Measure Your BMI Index?
Your body mass index (BMI) is a straightforward measurement that compares your weight to your height. Measuring your BMI is quick and easy — you just need two numbers: your weight in kilograms and your height in metres. The NHS uses BMI as a screening tool to check whether you're at a healthy weight for your height. In this guide, we'll explain exactly how to calculate your BMI, what your result means, and how to use our free BMI calculator to find your personal number instantly.
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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.
The BMI Formula and How to Calculate It
The BMI formula is simple: divide your weight in kilograms by your height in metres squared. For example, if you weigh 70kg and are 1.75 metres tall, your calculation is: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI. Use our free BMI calculator above to find your result instantly without doing the maths yourself. Once you have your number, compare it to the NHS BMI categories below to see where you fall.
- 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 range UK thresholds — ask your GP for guidance specific to your background, as these groups face higher health risks at lower BMI levels.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
BMI Limitations and What Else Matters
While BMI is useful, it has important limitations. BMI limitations include: it doesn't distinguish between muscle and fat (athletes may have high BMI but low body fat), it doesn't account for where fat is stored on your body, and it may be less accurate for older adults or during pregnancy. The NHS recommends also measuring your waist circumference: men should aim for under 94cm (37 inches), and women under 80cm (31.5 inches). For a fuller picture of your health, discuss your weight and BMI with your GP — they can assess your individual risk factors and overall wellness beyond just a number.
- 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 range?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9. This range is associated with the lowest health risks for most UK adults. If your BMI falls outside this range, your GP can advise on next steps tailored to your health.
How do I measure my BMI if I'm very tall or very short?
The BMI formula works for all heights. The key is accurate measurements: weigh yourself on reliable scales and measure your height precisely in metres (or convert feet/inches to metres). Use our BMI calculator above — it handles all heights correctly.
Is the overweight BMI threshold the same for everyone?
Not entirely. The overweight BMI threshold is normally 25.0 for most UK adults. However, adults of South Asian, Chinese, Black African, or Black Caribbean descent may qualify for earlier intervention at lower BMI levels due to higher disease risk. Your GP can advise you personally.
Why does the NHS use BMI when it has limitations?
BMI is quick, cheap, and works well for screening most people. The NHS doesn't rely on BMI alone — your GP will also consider your waist measurement, blood pressure, blood sugar, and overall health. It's one tool among many, not the complete picture.
Can I use the weight converter to help calculate my BMI?
Yes. Convert your weight between kg, stone, and lbs using our free weight converter, then use the BMI calculator with your weight in kilograms. Having your weight in both units helps you understand your personal numbers in a format you're familiar with.
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.