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 Calculate BMI — NHS Formula and Categories
BMI (Body Mass Index) is a simple measurement that helps assess whether your weight is healthy for your height. The BMI formula divides your weight in kilograms by your height in metres squared. Understanding how to calculate your BMI is the first step in assessing your weight health according to NHS guidelines. The NHS uses BMI as a screening tool to identify whether adults fall into healthy, overweight, or obese categories. However, BMI has important limitations — it doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a higher BMI despite being healthy. Use our free BMI calculator above to instantly calculate your personal BMI, or follow the formula below to work it out yourself.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 straightforward: divide your weight in kilograms by your height in metres, squared. Mathematically: BMI = weight (kg) ÷ height (m)²
For example, if you weigh 70kg and are 1.75 metres tall: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9
Once you have your BMI number, compare it to the NHS 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 to 39.9: Obese (Class II)
- 40.0 and above: Severely obese (Class III)
Important: for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds. A healthy BMI range for these groups is 18.5 to 22.9, and overweight starts at 23.0.
Clinically BackedWeight Loss
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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 Guidance and When to Seek Help
The NHS uses BMI as part of its weight management pathway. If your BMI falls outside the healthy range, the NHS recommends speaking to your GP, especially if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can offer support through NHS weight management services, which range from digital tools and community programmes (Tier 1) to specialist referrals (Tier 3). Remember that BMI has limitations — it doesn't account for muscle mass, bone density, or where fat is stored (central fat around the abdomen carries higher health risks). Use the weight converter on this page to switch between kg, stone, and pounds as needed for your health records.
- 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 divides your weight in kilograms by your height in metres squared. For example, 70kg ÷ (1.75m × 1.75m) = 22.9 BMI. Use our free BMI calculator above to calculate yours instantly without doing the maths yourself.
What BMI range does the NHS consider healthy?
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 healthy range is lower: 18.5 to 22.9. Your GP can discuss what's healthy for you specifically.
Why are there different BMI thresholds for different ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean descent have a higher risk of type 2 diabetes and heart disease at lower BMI levels. The NHS adjusted thresholds for these groups to better identify health risks earlier.
Does a high BMI always mean I'm unhealthy?
Not necessarily. BMI doesn't distinguish between muscle and fat, so muscular athletes may have a high BMI but low body fat. However, for most people, a BMI above 30 indicates increased health risk. Your GP can assess your individual health beyond BMI alone.
What should I do if my BMI is outside the healthy range?
Speak to your GP, who can refer you to NHS weight management services if appropriate. The NHS offers support ranging from free digital tools and community programmes to specialist weight management services. Your GP can also discuss whether prescription weight loss treatment might be suitable for your circumstances.
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.