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 Check Your BMI Using The Simple Formula
Your BMI (body mass index) is calculated using a straightforward formula based on your weight and height. The NHS uses BMI as a key screening tool to assess whether an adult's weight falls into a healthy range. Understanding how to check your BMI formula helps you assess your personal weight status and identify whether you might benefit from lifestyle changes or medical support. This guide explains the calculation, NHS categories, and what your result means for your health according to current UK guidance.
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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 calculate, divide your weight in kilograms by your height in metres, then divide by your height again. For example, at 70kg and 1.75m tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy weight range.
The NHS BMI range categories are:
- Below 18.5: Underweight
- 18.5 to 24.9: Healthy weight
- 25.0 to 29.9: Overweight
- 30.0 to 34.9: Obese (Class I)
- 35.0 to 39.9: Obese (Class II)
- 40.0+: Severely obese (Class III)
These bmi categories uk are standard across NHS services. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — with a healthy weight range of 18.5 to 22.9 — because these groups face higher health risks 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.
Understanding BMI Limitations And NHS Support
BMI is a useful screening tool but has important bmi 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; waist circumference matters too. The NHS recommends measuring waist circumference alongside BMI: over 94cm in men or 80cm in women indicates increased health risk.
If your BMI suggests you may be overweight or obese, the NHS weight management pathway starts with your GP. They can assess your overall health, discuss lifestyle support, refer you to tier 3 specialist services, or — if clinically appropriate — consider prescription options. Use our free BMI calculator above to check your personal BMI instantly, then speak with your GP about next steps tailored to your individual health.
- 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 easiest way to calculate my BMI quickly?
Use our free BMI calculator on this page — it converts your measurements automatically. If calculating manually, divide your weight in kg by your height in metres squared. For example, 80kg ÷ (1.80 × 1.80) = 24.7 BMI. This takes seconds once you know your exact height and weight.
Does the NHS BMI formula differ from other countries?
No — the formula (weight in kg ÷ height in metres²) is the same globally. However, NHS BMI categories and healthy weight thresholds are UK-specific. The NHS also applies lower thresholds for South Asian and other ethnic groups due to higher cardiovascular disease risk at lower BMI levels.
Why does the NHS use BMI if it has limitations?
BMI is a quick, non-invasive screening tool useful for identifying who may benefit from health support. The NHS acknowledges BMI limitations — it's always used alongside other measures like waist circumference, blood pressure, and blood sugar levels. Your GP considers your complete health picture, not BMI alone.
If my BMI is in the healthy range, do I need to do anything?
If your BMI is 18.5 to 24.9 (or 18.5 to 22.9 if you're of South Asian heritage), the NHS recommends maintaining a healthy lifestyle: balanced diet, regular physical activity, and stress management. Check your BMI periodically and contact your GP if you notice changes or have health concerns.
What should I do if my BMI shows I'm overweight or obese?
Contact your GP for a health check. They can assess your overall health, discuss diet and exercise support, refer you to specialist weight management services, or — if appropriate and following clinical assessment — discuss prescription weight loss options like GLP-1 injections alongside lifestyle changes.
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.