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 Measure BMI — NHS Guidance
BMI (Body Mass Index) is a simple screening tool used by the NHS to assess whether an adult's weight falls within a healthy range for their height. Measuring your BMI is straightforward — it requires only your height and weight — but understanding what the result means in an NHS context is equally important. This guide explains the standard BMI formula, NHS weight categories, and what to do if your BMI suggests you may need support managing your weight.
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 NHS BMI Formula and Categories
The BMI formula is the same across the UK and internationally. Divide your weight in kilograms by your height in metres squared: BMI = weight (kg) ÷ height (m)²
For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI.
The NHS uses these BMI categories for adults:
- 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)
Use our free BMI calculator above to find your personal BMI instantly, or convert your weight between kg, stone, and pounds using the weight converter on this page.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Pathways and Support
If your BMI falls outside the healthy range (18.5–24.9), the NHS recommends speaking to your GP, who can assess your individual health and discuss weight management options. For South Asian, Chinese, Black African, and Black Caribbean adults, the NHS recommends lower thresholds — a healthy BMI is 18.5–22.9 — because these groups face higher diabetes and heart disease risk at the same BMI levels.
The NHS offers a structured four-tier weight management pathway. Tier 1 includes self-help tools and community programmes; Tier 2 involves primary care interventions; Tier 3 is specialist multidisciplinary weight management services, where prescription medications like Mounjaro or Wegovy may be discussed; and Tier 4 is bariatric surgery for severe obesity. Your GP can guide you to the right tier based on your needs.
- 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 NHS guidance?
According to NHS guidelines, a healthy BMI for most UK adults is between 18.5 and 24.9. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a healthy range of 18.5 to 22.9 because these groups have higher health risks at the same BMI levels. Your GP can discuss your personal healthy weight range.
How do I calculate BMI if my weight is in stone and pounds?
Convert your weight to kilograms first. One stone equals 6.35 kg, and one pound equals 0.454 kg. Use our weight converter above to switch between stone, pounds, and kilograms instantly. Then apply the formula: BMI = weight (kg) ÷ height (m)².
What are the limitations of BMI?
BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also does not account for where fat is stored (waist measurement matters too) and is less accurate for elderly people or during pregnancy. BMI is a screening tool, not a complete health assessment. Always discuss your results with your GP.
What should I do if my BMI is outside the healthy range?
Speak to your GP, who can assess your health, discuss any weight-related conditions, and recommend appropriate support. This might include lifestyle advice, structured weight management programmes, or — if eligible — prescription weight loss medication through NHS specialist services.
Why are BMI thresholds different for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage face higher risks of type 2 diabetes and heart disease at lower BMI levels. The NHS therefore recommends lower BMI thresholds (18.5–22.9 for healthy weight) for these groups to ensure earlier intervention and better health outcomes.
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.