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 Test Your BMI — A Simple Guide
Testing your BMI (Body Mass Index) is straightforward and takes just two measurements: your weight and height. The NHS uses BMI as a screening tool to assess whether you're in a healthy weight range. Simply use the BMI formula, enter your measurements into a calculator, or use our free BMI calculator above to find your number instantly. Understanding your BMI range helps you know where you stand health-wise, though it's important to remember that BMI has limitations and doesn't account for muscle mass or fat distribution. Let's explore how to calculate it and what your result means.
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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: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your calculation would be 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI. If you prefer using stone and pounds, convert first: 70kg equals approximately 11 stone 0.1lbs — use our free weight converter to switch between units instantly. Once you have your BMI number, match it against the NHS BMI categories: under 18.5 is underweight, 18.5–24.9 is healthy BMI, 25–29.9 is overweight, 30–34.9 is obese class I, 35–39.9 is obese class II, and 40+ is severely obese. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy bmi range is slightly lower (18.5–22.9) due to higher health risks at lower weights. Use our BMI calculator above for gradual improvement — simply enter your weight and height to see your category immediately.
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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.
Understanding BMI Limitations and Other Health Measures
BMI limitations are important to understand. BMI does not distinguish between muscle and fat — athletes or very muscular individuals may have a high BMI but low body fat. It also ignores where fat is stored; visceral fat around the organs carries more health risk than subcutaneous fat. BMI is less accurate for elderly people due to natural muscle loss with age, and it's not suitable during pregnancy. The NHS recommends using waist circumference alongside BMI: for men, over 94cm (37in) indicates increased risk; over 102cm (40in) is high risk. For women, over 80cm (31.5in) indicates increased risk; over 88cm (34.5in) is high risk. For a complete picture, combine your BMI result with waist measurement and discuss any concerns with your GP, who can assess your overall cardiovascular risk and health status.
- 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 normal BMI range in the UK?
According to NHS guidelines, a healthy BMI is 18.5 to 24.9 for most UK adults. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5 to 22.9 due to higher disease risk at lower BMI levels.
How do I convert my weight to use the BMI formula?
If your weight is in stone and pounds, convert to kilograms first using 1 stone = 6.35kg. Height must be in metres — divide centimetres by 100. For example, 5ft 8in (173cm) = 1.73m. Use our free weight converter above to switch units instantly.
Can BMI be inaccurate?
Yes. BMI doesn't account for muscle mass, so athletes may have a high BMI despite low body fat. It also ignores fat distribution and is less reliable for elderly people, pregnant women, and very tall or short individuals. Always combine BMI with waist circumference for a fuller picture.
What should I do if my BMI is in the overweight or obese range?
Discuss your results with your GP, who can assess your overall health and recommend next steps. The NHS offers tier 1 weight management support including the NHS Weight Loss Plan, and referral to specialist services if needed. Small lifestyle changes can make a real difference.
Is BMI the only measure of healthy weight?
No. The NHS also recommends checking waist circumference — excess weight around the stomach carries higher health risks. Your GP can give you personalised advice about what a healthy weight means for you based on your age, medical history, and other factors.
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.