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 Count Your BMI — The Complete UK Guide
Counting your BMI (Body Mass Index) is straightforward using a simple mathematical formula based on your weight and height. The NHS uses BMI as a key screening tool to assess whether an adult's weight is in a healthy range. Understanding how to calculate your BMI and what the result means can help you make informed decisions about your health. Use our free BMI calculator above to find your result instantly, or read on to learn how to count it manually and what the NHS BMI categories mean for you.
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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 Count Your BMI — The Formula and NHS Categories
The BMI formula is simple: divide your weight in kilograms by your height in metres, squared. The formula is: BMI = weight (kg) ÷ height (m)²
Example: If you weigh 70kg and are 1.73m tall, your BMI = 70 ÷ (1.73 × 1.73) = 70 ÷ 2.99 = 23.4
The NHS BMI range divides adults into four main categories:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese: BMI 30.0 and above
People of South Asian, Chinese, Black African, or Black Caribbean heritage have a higher health risk at lower BMI levels, so the NHS recommends lower BMI categories UK thresholds for these groups: healthy weight 18.5–22.9, and overweight from 23.0. For anyone concerned about what their BMI means, your GP can provide personalised health guidance.
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 for Health
BMI limitations are important to understand. BMI cannot distinguish between muscle and fat — athletes or people with high muscle mass may have a high BMI but low body fat. BMI also does not account for where fat is stored; waist circumference is equally important. Healthy BMI is a useful screening tool, but it is not a complete picture of health.
The NHS recommends measuring your waist as well: men should aim for under 94cm (37 inches), women under 80cm (31.5 inches). Age, ethnicity, bone density, and medical conditions all affect what weight is healthy for you personally. Use our weight converter to check your weight in different units, and speak to your GP if you have concerns about your health or weight.
- 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?
According to NHS guidelines, a healthy BMI for most adults is between 18.5 and 24.9. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower threshold: 18.5 to 22.9. Your GP can advise on what is healthy for you personally.
How do I count my BMI if I use stone and pounds?
Convert your weight to kilograms first (divide stone and pounds by 6.35029), and your height to metres. Then use the formula: BMI = weight (kg) ÷ height (m)². Alternatively, use our free BMI calculator on this page — it handles all unit conversions automatically.
What BMI is considered overweight in the UK?
The overweight BMI threshold in the UK is 25.0 to 29.9 according to NHS guidelines. A BMI of 25 or above may increase health risks, though individual factors like age, muscle mass, and ethnicity affect this. Your GP can assess your personal risk.
Does BMI tell you everything about your health?
No. BMI has important limitations — it cannot distinguish muscle from fat, does not account for where fat is stored, and does not consider age, bone density, or medical conditions. The NHS also recommends measuring your waist circumference alongside BMI for a fuller picture of health risk.
Can I use the BMI calculator instead of counting it manually?
Yes. Our free BMI calculator on this page will count your BMI instantly and show you the NHS categories. It handles conversions between stone, pounds, kilograms, and imperial measurements automatically, making it faster and more accurate than a UK pharmacy calculation.
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.