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 Work Your BMI Out
Working out your BMI is straightforward — you just need your weight in kilograms and your height in metres. BMI (Body Mass Index) is a useful screening tool that helps you understand whether your weight falls within a healthy range according to NHS guidelines. In just a few seconds, you can calculate your personal BMI using our free BMI calculator on this page, or follow the simple formula below to work it out manually.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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: weight (kg) ÷ height (m)²
Here's how to work it out step by step:
- Step 1: Measure your height in centimetres and convert to metres (divide by 100). For example, 170cm = 1.70m
- Step 2: Multiply your height in metres by itself. For example, 1.70 × 1.70 = 2.89
- Step 3: Divide your weight in kilograms by this number. For example, 75kg ÷ 2.89 = BMI of 25.9
A BMI of 25.9 falls into the overweight category according to NHS guidelines. You can instantly calculate your exact BMI and see which category you fall into using the BMI calculator above.
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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.
Understanding Your BMI Result and NHS Categories
Once you've calculated your BMI, the next step is understanding what it means. According to NHS BMI categories, the standard healthy BMI range is 18.5 to 24.9. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 and above is obese (with further classifications above that).
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the overweight BMI threshold is lower — the NHS-recommended healthy range for these groups begins at 18.5 and extends only to 22.9, because these populations face higher health risks at lower BMI levels. Your GP can discuss what a healthy weight means specifically for you, taking into account your individual circumstances.
- 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's the difference between calculating BMI in kg and in pounds?
The BMI formula remains the same regardless of units, but it's easier in metric (kg and metres). For pounds and inches, the formula is: (weight in lbs × 703) ÷ height (inches)². However, the NHS uses kilograms, so converting to metric first is more straightforward for UK health comparisons.
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 a high BMI but low body fat. BMI also doesn't account for where fat is stored or variations due to age, bone density, or ethnicity. Use BMI alongside other measures like waist circumference and talk to your GP for a complete health picture.
What's a healthy BMI range for UK adults?
According to NHS guidelines, a healthy BMI range is 18.5 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 due to higher health risks at higher BMI levels in these populations.
Can I use the BMI calculator instead of working it out manually?
Yes — our free BMI calculator on this page instantly calculates your BMI when you enter your weight and height. It's faster and eliminates the chance of calculation errors. The calculator also shows you which NHS category your BMI falls into and explains what it means.
Does a high BMI definitely mean I'm unhealthy?
A high BMI is a screening indicator of increased health risk, but it's not a diagnosis. Some people with a high BMI are metabolically healthy, whilst others with a normal BMI may have underlying health conditions. Your GP can assess your individual health through blood tests, lifestyle factors, and overall fitness — BMI is just one piece of the picture. ```
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.