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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How To Calculate Your Healthy BMI — NHS Guidance
Calculating your BMI is straightforward using a simple formula, and understanding what your result means according to NHS guidelines can help you assess your health. BMI (Body Mass Index) is a screening tool that uses your height and weight to estimate whether you're at a healthy weight. The NHS uses standardised BMI categories to help you understand your result and whether your weight may affect your health. Using our free BMI calculator above is the quickest way to get your personal BMI instantly, but learning the formula helps you understand what the number actually means.
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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.
BMI Formula and NHS Categories
The BMI formula is simple: divide your weight in kilograms by your height in metres squared. In metric: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.73m tall, your BMI would be 70 ÷ (1.73 × 1.73) = 23.4.
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)
Importantly, the NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage, as these groups face higher health risks at lower BMI levels. For these populations, a healthy BMI is 18.5 to 22.9, overweight starts at 23.0, and obesity at 27.5.
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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 and Important Limitations
The NHS encourages adults to maintain a BMI in the healthy range (18.5 to 24.9) as part of overall health. Your GP can discuss your personal BMI and what it means for your wellbeing. However, BMI has important limitations—it doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. BMI also doesn't account for where fat is stored; waist circumference is another useful measure. Pregnant women, elderly people, and those with very high muscle mass may find BMI less accurate. For a comprehensive health picture, your GP may also check your waist measurement and other health markers.
- 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 healthy BMI as 18.5 to 24.9 for most adults. For South Asian, Chinese, Black African, and Black Caribbean adults, the healthy range is 18.5 to 22.9 due to higher health risks at lower BMI levels. Your GP can advise on what's healthy for you personally.
How do I calculate BMI from stone and pounds?
First convert stone and pounds to kilograms (1 stone = 6.35kg, 1 lb = 0.454kg). Then use the BMI formula: weight (kg) ÷ height (m)². Alternatively, use our free weight converter and BMI calculator above to do this instantly.
Why does the NHS give lower BMI thresholds to some ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults have higher risks of type 2 diabetes and heart disease at lower BMI levels compared to white European populations. Lower thresholds help identify health risks earlier in these groups.
What should I do if my BMI is in the overweight range?
The NHS recommends discussing your BMI with your GP, who can assess your overall health and weight-related risk factors. Small lifestyle changes—such as increased activity and modest dietary changes—often help. If appropriate, your GP may refer you to NHS weight management services.
Is BMI accurate for everyone?
BMI is useful for screening but has limitations. It doesn't account for muscle mass, bone density, or fat distribution. Pregnant women, children, elderly people, and very muscular individuals may find BMI less accurate. Your GP can provide a more complete health assessment beyond 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.