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 — A Clear NHS Guide
Getting your BMI (Body Mass Index) is straightforward and takes just two pieces of information: your weight and height. The NHS uses BMI as a key screening tool to assess whether your weight falls within a healthy range for your height. Your BMI helps your GP understand your health risk and whether you might benefit from support with weight management. We'll show you exactly how to calculate it, what the NHS BMI categories mean, and where to go for personalised guidance. Use our free BMI calculator above to find your result instantly, or follow our simple step-by-step method below.
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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.
Understanding the BMI Formula and NHS Categories
The BMI formula is simple: divide your weight in kilograms by your height in metres squared (BMI = weight kg ÷ height m²). For example, someone who weighs 70kg and is 1.75m tall would calculate: 70 ÷ (1.75 × 1.75) = 22.9 BMI. The NHS uses this calculation to place you into one of five BMI categories:
- 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 and above: Severely obese (Class II or III)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — your healthy BMI range is 18.5 to 22.9, and overweight starts at 23.0. This reflects higher health risks at lower BMI levels for these populations. Try our free BMI calculator on this page to find your category instantly.
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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 Support and When to Seek Help
If your BMI suggests you're overweight or obese, the NHS offers a structured approach called the weight management pathway. At Tier 1, your GP can signpost you to free community programmes and the NHS Weight Loss Plan (available online). For ongoing support, Tier 2 services provide behaviour change coaching. If you have health complications — such as type 2 diabetes, high blood pressure, or sleep apnoea — Tier 3 specialist services may be appropriate, where prescription weight loss medication might be considered. Your GP can assess your individual situation and refer you to the right service. Remember that BMI has limitations — it doesn't account for muscle mass, bone density, or where fat is stored, so your GP will always consider your full health 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 a healthy BMI according to the NHS?
The NHS defines a healthy BMI as 18.5 to 24.9 for most adults. For people of South Asian, Chinese, Black African, or Black Caribbean descent, the healthy range is 18.5 to 22.9. A BMI in this range indicates your weight is proportionate to your height and typically poses lower health risks.
How do I calculate my BMI if I use stone and pounds?
Convert your weight to kilograms first. One stone equals 6.35 kg, so multiply your stone by 6.35 and add your pounds converted to kg (divide by 2.2). Then divide by your height in metres squared. Our free weight converter above can help you switch between stone, pounds, and kilograms instantly.
What should I do if my BMI is above the healthy range?
Start by speaking with your GP, who can assess your individual health and discuss your options. The NHS offers free support through Tier 1 services including online weight loss plans and community programmes. Depending on your health conditions and BMI level, you may be eligible for further support through specialist services or prescription weight loss medication.
Why are BMI thresholds different for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher risks of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS recommends lower thresholds for these groups to ensure early identification of health risk and earlier intervention when needed.
Does a high BMI definitely mean I'm unhealthy?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, so athletes may have high BMI but excellent health. Your GP considers your BMI alongside waist measurement, blood pressure, blood tests, and overall health picture for a complete assessment. ```
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.