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 Get Your BMI
Your BMI (Body Mass Index) is a simple measurement that shows whether your weight falls within a healthy range for your height. Getting your BMI takes just two measurements — your weight and height — and a quick calculation using the NHS formula. Understanding your BMI is an important first step in assessing your overall health risk. Our free BMI calculator above does this instantly, but it's also useful to know how the calculation works and what your result actually means 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 Calculate Your BMI Using the NHS Formula
The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared. In mathematical terms: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75 metres tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy BMI range.
If you prefer working in stone and pounds, convert your weight to kilograms first: multiply stone by 6.35 and add the pounds converted (pounds × 0.454). Then apply the same formula. The NHS uses this metric calculation as the standard.
For the most accurate result, use our free BMI calculator above — it handles the conversion and calculation instantly. You only need to enter your weight (in kg, stone, or lbs) and height (in cm or feet and inches), and your result appears immediately with your BMI category UK classification.
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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 have your BMI number, the NHS classifies it into categories. A healthy BMI range is 18.5 to 24.9. Between 25 and 29.9 is overweight, 30 to 34.9 is obese (Class I), 35 to 39.9 is obese (Class II), and 40 or above is severely obese. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply — your healthy range starts at 18.5 and overweight begins at 23. Your GP can explain what your specific BMI means for your individual health and whether any action is needed.
It's important to remember that BMI limitations exist — the measurement doesn't distinguish between muscle and fat, so muscular individuals may have a higher BMI despite low body fat. BMI also doesn't account for where fat is stored on your body. Your waist circumference is equally important: the NHS recommends keeping it below 94cm for men and 80cm for women. Using our weight converter, you can also track how your weight changes over time and see the impact on your BMI. For a complete picture of your health, combine BMI with waist measurement, fitness level, and regular GP check-ups.
- 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.
Can I calculate BMI using stone and pounds instead of kilograms?
Yes, you can convert first or use the imperial formula: BMI = (weight in pounds × 703) ÷ height in inches squared. However, the NHS standard uses kilograms and metres. Our BMI calculator accepts stone, pounds, and kilograms, so you can enter your weight in whichever unit you prefer.
What's the difference between a healthy BMI and a healthy weight?
BMI is a screening tool based on height and weight ratio. A healthy weight is your actual weight in kg or stone. Your healthy weight range depends on your height — use our free BMI calculator to find the range for you. For example, at 1.70m tall, the healthy weight range is approximately 53–72kg.
Is BMI accurate for everyone?
No. BMI doesn't account for muscle mass, bone density, age, or where fat is stored. Athletes may have high BMI but low body fat. Older adults and pregnant women may need different assessment methods. Always discuss your BMI with your GP for personalised health advice.
How often should I check my BMI?
The NHS recommends checking your BMI periodically — typically every few months if you're working on weight management, or annually as part of general health monitoring. Our free progress tracker can help you log changes over time and see trends in your weight and BMI.
What should I do if my BMI is in the overweight or obese range?
If your BMI falls above the healthy range, speak to your GP. They can assess your overall health, discuss lifestyle changes like diet and exercise, and recommend appropriate support. NHS tier 3 weight management services are available in some areas, and your GP can refer you if needed.
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.