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 Determine Your BMI Using NHS Guidelines
Determining your BMI (Body Mass Index) is one of the first steps in understanding your weight and health. The NHS uses BMI as a screening tool to assess whether an adult's weight falls within a healthy range. Your BMI is calculated using a simple formula based on your weight and height, and the result helps identify whether you're in the underweight, healthy weight, overweight, or obese category. Use our free BMI calculator above to determine your BMI instantly, or learn how to calculate it manually using the NHS formula and understand what your result means for your health.
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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.
NHS BMI Categories and What They Mean
The NHS defines five BMI categories for adults, each with different health implications. According to NHS guidelines, a healthy BMI range is between 18.5 and 24.9. A BMI below 18.5 is classified as underweight, while 25.0 to 29.9 falls into the overweight category. BMI of 30.0 to 34.9 is classed as obese (Class I), 35.0 to 39.9 as obese (Class II), and 40.0 or above as severely obese (Class III).
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds due to higher health risks at the same BMI. For these groups, a healthy range is 18.5 to 22.9, and overweight starts at 23.0. This reflects evidence that these populations face greater risk of type 2 diabetes and heart disease at lower BMI levels. Your GP can discuss whether these adjusted thresholds apply to you.
The BMI formula used is: weight (kg) ÷ height (m)². Converting to stone? Use our weight converter to switch between kilograms, stone, and pounds, then calculate your BMI using your preferred units.
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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 Pathway and When to Seek Help
If your BMI falls outside the healthy range, the NHS provides a structured weight management pathway with support at different levels. Tier 1 begins with self-help resources and community programmes; Tier 2 involves your GP and primary care weight loss support such as the NHS Weight Loss Plan. For those with a BMI of 30 or above with related health conditions, Tier 3 specialist services offer multidisciplinary weight management including dietitian support, behaviour change coaching, and in some cases, prescription weight loss medications. Tier 4 covers bariatric (weight loss) surgery for severe obesity with significant health complications.
Contact your GP if you're concerned about your weight or have weight-related health conditions. Your GP can assess your individual situation, discuss lifestyle changes, and refer you to appropriate NHS services if needed. Many areas also offer free digital weight management tools and community support programmes.
- 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.
How do I calculate my BMI if I use stone and pounds?
Convert your weight to kilograms first using our weight converter, then use the formula: BMI = weight (kg) ÷ height (m)². For example, 11 stone (70kg) at 1.73m height gives a BMI of approximately 23.4, which falls in the healthy range. Our BMI calculator does this instantly for you.
What are the BMI limitations I should know about?
BMI doesn't distinguish between muscle and fat, so athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored (waist measurement matters too) or changes due to age. BMI is less accurate during pregnancy and for elderly adults. Always discuss your individual health with your GP.
Why are BMI thresholds different for some ethnic groups?
The NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults because research shows these groups face higher risk of type 2 diabetes and heart disease at lower BMI levels. For these groups, a healthy BMI starts at 18.5 and overweight begins at 23.0 rather than 25.0.
When should I contact my GP about my BMI?
Contact your GP if your BMI is above 25, especially if you have weight-related health conditions like high blood pressure, type 2 diabetes, sleep apnoea, or heart disease. Your GP can assess your health, discuss lifestyle changes, and refer you to NHS weight management services if appropriate.
What does the NHS recommend for healthy weight loss?
The NHS recommends losing weight at a rate of 0.5 to 1 kg (1 to 2 lbs) per week, achieved through a calorie deficit of around 500 calories per day alongside increased physical activity. This approach is sustainable and reduces the risk of muscle loss, helping maintain long-term weight management success.
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.