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 Using The NHS Formula
Understanding how to count your BMI formula is straightforward and gives you a quick snapshot of your weight in relation to your height. The BMI formula used by the NHS is simple: divide your weight in kilograms by your height in metres squared. This page explains the exact calculation, shows you how to work it out manually, and helps you understand what your BMI result means according to NHS guidance. Whether you prefer calculating manually or using our free BMI calculator above, knowing the formula itself is empowering for managing your health.
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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 NHS Categories Explained
The BMI formula is: weight (kg) ÷ height (m)². To use it, measure your height in metres (for example, 1.73m for 5ft 8in), then divide your weight in kilograms by that height multiplied by itself. For example, a person weighing 70kg and 1.73m tall would calculate: 70 ÷ (1.73 × 1.73) = 70 ÷ 2.99 = 23.4 BMI.
The NHS uses these BMI categories for UK adults:
- Below 18.5 = underweight
- 18.5–24.9 = healthy weight
- 25.0–29.9 = overweight
- 30.0–34.9 = obese (Class I)
- 35.0–39.9 = obese (Class II)
- 40.0+ = severely obese (Class III)
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: healthy weight is 18.5–22.9, and overweight starts at 23.0. These lower BMI range thresholds reflect higher cardiovascular and diabetes risk in these populations at lower BMI levels.
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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.
NHS Weight Management And When To Seek Support
If your BMI falls outside the healthy range, the NHS offers support through its weight management pathway. Tier 1 involves self-help resources and digital tools like the BMI calculator on this page. Tier 2 includes GP-led behaviour change programmes and community weight management services. Tier 3 offers specialist multidisciplinary weight management services, where prescription medications may be considered for eligible adults. Speak to your GP if you're concerned about your weight or want to discuss your BMI result—they can provide personalised advice and access to NHS support tailored to your individual health needs.
Remember that BMI has limitations: it doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. BMI limitations also include that it doesn't account for where fat is stored on your body. The NHS recommends using BMI alongside waist circumference measurements for a fuller picture. For men, increased health risk begins at a waist circumference over 94cm (37in); for women, over 80cm (31.5in). Use our free weight converter to track your weight in both metric and imperial units, making it easier to monitor changes over time and discuss your weight with your GP.
- 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 in kilograms divided by height in metres squared. For example, if you weigh 75kg and are 1.70m tall, calculate: 75 ÷ (1.70 × 1.70) = 75 ÷ 2.89 = 26.0 BMI. This places you in the overweight category according to NHS guidelines.
Is the BMI formula different for men and women?
No, the BMI formula is identical for men and women. However, the NHS recommends lower BMI thresholds for people of certain ethnic backgrounds, and the healthy weight range may be interpreted differently based on individual health factors. Your GP can advise on what your BMI means for you personally.
What is a healthy BMI according to the NHS?
A healthy BMI according to the NHS is between 18.5 and 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a healthy range of 18.5 to 22.9 due to higher health risks at higher BMI levels in these groups.
Why does the NHS use BMI if it has limitations?
The NHS uses BMI because it's a quick, simple screening tool that works well for most populations. However, BMI doesn't account for muscle mass, fat distribution, or other health factors. That's why your GP may also measure waist circumference and discuss your overall health rather than relying on BMI alone.
How often should I calculate my BMI to track my weight?
The NHS recommends checking your weight and BMI approximately monthly rather than daily, as weight naturally fluctuates. Our free BMI calculator and progress tracker can help you log changes over time and identify trends. Regular monitoring helps you and your GP spot meaningful changes and adjust health strategies 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.