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
BMI and Body Weight — What NHS Guidelines Say
Your body mass index (BMI) is a measure of whether your body weight sits within a healthy range for your height. The NHS uses BMI as a screening tool to assess weight-related health risks in UK adults. However, BMI is just one part of the picture — your GP may also consider other factors like waist circumference, fitness level, and personal health history. Understanding your BMI and what it means for your health is an important first step in managing your weight and wellbeing. Use our free BMI calculator above to find out your personal BMI instantly.
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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 the following BMI categories to classify weight status in UK adults:
- Underweight: BMI below 18.5 — may indicate insufficient nutrition or underlying health issues
- Healthy weight: BMI 18.5 to 24.9 — associated with the lowest health risks
- Overweight: BMI 25.0 to 29.9 — increased risk of type 2 diabetes and heart disease
- Obese (Class I): BMI 30.0 to 34.9 — moderate risk of weight-related health conditions
- Obese (Class II): BMI 35.0 to 39.9 — high risk of serious health complications
- Severely obese (Class III): BMI 40.0 and above — very high health risk requiring medical attention
For people of South Asian, Chinese, Black African, or Black Caribbean descent, the NHS recommends lower thresholds because these groups face higher cardiovascular and metabolic risks at the same BMI. Healthy weight for these populations is BMI 18.5 to 22.9, with overweight starting at 23.0. Your GP can advise whether adjusted thresholds apply to you. Calculate your personal BMI range using the calculator on this page to see where you currently sit.
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.
Important BMI Limitations and the Bigger Picture
While BMI is a useful screening tool, it has significant BMI limitations — it does not distinguish between muscle and fat. Athletes or very muscular individuals may have a high BMI but low body fat. BMI also does not account for where fat is stored; excess fat around the abdomen carries greater health risk than fat distributed elsewhere. For older adults, muscle loss with age can skew results. That is why the NHS also measures waist circumference: for men, over 94cm (37 inches) indicates increased risk; over 102cm (40 inches) is high risk. For women, over 80cm (31.5 inches) is increased risk; over 88cm (34.5 inches) is high risk. Your GP may use BMI alongside these measurements and your personal health history to give you tailored advice about your weight and health.
- 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 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean background, the NHS recommends a lower range of 18.5 to 22.9 because these groups have higher metabolic disease risk at higher BMI levels. Your GP can advise on what range is right for you personally.
How do I work out my BMI from my body weight?
BMI is calculated as weight in kilograms divided by height in metres squared (kg ÷ m²). For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. You can use our free BMI calculator above for gradual improvement without doing the maths yourself.
When should I speak to my GP about my weight?
Speak to your GP if your BMI is consistently above 25, if you have gained weight rapidly, if weight is affecting your health or mobility, or if you have symptoms like fatigue, breathlessness, or joint pain. Your GP can assess your individual risk and discuss weight management options or referral to specialist services if appropriate.
What does the NHS offer for weight management?
The NHS offers weight management support through four tiers: tier 1 includes self-help and digital tools, tier 2 includes behaviour change programmes, tier 3 includes specialist multidisciplinary services (where weight loss medications may be prescribed), and tier 4 includes bariatric surgery for severe obesity. Access and waiting times vary by region.
Does high BMI always mean I am unhealthy?
Not necessarily — BMI is a screening tool, not a diagnosis. Some people with higher BMI may be in good health, while others with BMI in the normal range may have health risks. Your GP considers BMI alongside fitness, medical history, waist measurement, blood pressure, and blood tests to assess your overall health.
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.