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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Understanding Your BMI in Stone — NHS Guidance
Your BMI (body mass index) is a key health screening tool used by the NHS to assess whether your weight is in a healthy range for your height. In the UK, we typically measure weight in stone and pounds, which can make BMI calculations less intuitive than using kilograms. This guide explains NHS BMI categories, how they apply to you, and what the NHS recommends if your BMI falls outside the healthy range. Use our free BMI calculator above to find your personal BMI instantly, and explore what it means for your health.
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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.
NHS BMI Categories and What They Mean
The NHS uses standardised BMI categories to classify weight status in UK adults. These thresholds are based on health risk research and apply regardless of whether you measure your weight in stone, kilograms, or pounds.
- Healthy weight: BMI 18.5–24.9 — associated with the lowest health risks
- Overweight: BMI 25.0–29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0–34.9 — significantly increased health risks
- Obese (Class II): BMI 35.0–39.9 — high health risks
- Severely obese (Class III): BMI 40.0 and above — very high health risks
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 18.5–22.9, and overweight begins at 23.0. This is because these populations face higher cardiovascular and diabetes risk at lower BMI levels. Calculate your BMI now using the calculator on this page to find your personal category.
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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 falls outside the healthy range, the NHS offers a structured weight management pathway to support you. NICE guidance recommends that GPs assess all adults with overweight or obesity, discuss health risks, and offer lifestyle support as a first step.
- Tier 1: Self-help, digital tools, and community programmes through your GP
- Tier 2: GP-led behaviour change support and dietary advice
- Tier 3: Specialist multidisciplinary weight management services (referral from your GP)
- Tier 4: Bariatric surgery services for severe obesity with significant health complications
Your GP can refer you to appropriate support based on your BMI, health conditions, and readiness to make changes. If you're concerned about your weight or health, book an appointment with your GP who can discuss your options and provide personalised guidance.
- 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 18.5–24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower at 18.5–22.9 due to higher disease risk at higher BMI levels. Use our BMI calculator above to check your personal BMI.
How do I calculate my BMI in stone?
First, convert your stone and pounds to kilograms using our free weight converter. Then use the formula: BMI = weight (kg) ÷ height (m)². Our BMI calculator handles this automatically — just enter your weight in stone and height in feet and inches.
Why are NHS thresholds different for different ethnicities?
Research shows that some ethnic groups — South Asian, Chinese, Black African, and Black Caribbean populations — have higher risk of type 2 diabetes and heart disease at lower BMI levels. The NHS recommends adjusting thresholds to reflect these differences and ensure earlier intervention for at-risk groups.
What should I do if my BMI is above 25?
The NHS recommends speaking with your GP. They can assess your overall health, discuss any weight-related symptoms, and offer support through the weight management pathway. This may include lifestyle advice, digital tools, or referral to specialist services depending on your needs.
Are BMI limitations acknowledged by the NHS?
Yes. The NHS recognises that BMI does not account for muscle mass, bone density, or fat distribution. It is a useful screening tool but should be combined with other measures like waist circumference and overall health assessment. Your GP will consider your complete health picture, not BMI alone.
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.