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 Count BMI Using The Formula
The BMI formula is a straightforward calculation that takes your weight and height to give a number that indicates whether you're in a healthy weight range. Whether you use kilograms and metres (metric) or stones and pounds (imperial), the maths is simple — and our free BMI calculator above will do it instantly for you. But understanding how to count BMI yourself is useful for tracking your health. This guide explains both methods and what your result means according to NHS guidelines.
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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 Explained — Both Methods
Metric method (kilograms and metres): This is the NHS standard. The formula is: BMI = weight (kg) ÷ height (m)²
Example: If you weigh 70 kg and are 1.73 metres tall, your calculation is: 70 ÷ (1.73 × 1.73) = 70 ÷ 2.99 = 23.4 BMI
Imperial method (stones/pounds and inches): The formula is: BMI = (weight in lbs × 703) ÷ height (inches)²
Example: If you weigh 11 stone (154 lbs) and are 5ft 8in (68 inches) tall, your calculation is: (154 × 703) ÷ (68 × 68) = 108,262 ÷ 4,624 = 23.4 BMI
Once you have your number, check where it falls in the NHS BMI range categories to understand your result.
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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.
Why BMI Limitations Matter — And What Else To Consider
BMI is a useful screening tool, but it has important limitations. It cannot distinguish between muscle and fat — an athlete with high muscle mass may have a high BMI despite low body fat. It also does not account for where fat is stored on your body, which matters for health risk. The NHS recommends checking your waist circumference alongside BMI: men should aim for under 94 cm (37 inches), women under 80 cm (31.5 inches). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds due to higher health risks at the same weight. Use our free weight converter above to switch between units, and combine BMI with other health measures for a complete picture.
- 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 the BMI formula in simple terms?
BMI = weight (kg) ÷ height (m)². In imperial: (weight in lbs × 703) ÷ height (inches)². Both give the same result. Use our BMI calculator above for instant answers without doing the maths yourself.
What BMI range is healthy according to the NHS?
The NHS healthy weight BMI range is 18.5 to 24.9. For South Asian, Chinese, Black African, and Black Caribbean adults, the healthy range is 18.5 to 22.9 due to higher health risks at higher BMI levels.
Is BMI accurate for everyone?
No. BMI does not account for muscle mass, so athletes or very muscular individuals may have high BMI but low body fat. It also varies by age, ethnicity, and does not reflect where fat is stored. Always discuss your personal BMI with your GP.
Can I use BMI to calculate my ideal weight?
Yes. For any height, multiply the healthy BMI range (18.5–24.9) by your height in metres squared. For example, at 1.73m, healthy weight is roughly 55–74 kg (8st 10lbs to 11st 10lbs). Use our BMI calculator to find your range instantly.
What should I check alongside BMI?
The NHS recommends also measuring waist circumference. Men should aim for under 94 cm, women under 80 cm. Weight, diet, physical activity, and overall health matter too. Your GP can give personalised advice about what your BMI means for your individual health.
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.