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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BMI Classification in the UK — What Your BMI Number Means
BMI classification in the UK follows NHS guidelines that place adults into five main categories based on their BMI number. Your BMI classification determines whether your weight falls into a healthy range, or whether you may benefit from lifestyle changes or medical support. Understanding where you sit in the BMI classification system is an important first step in assessing your health risk. Use our free BMI calculator above to find your personal BMI instantly and see exactly where you fall within the UK classification system.
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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.
UK BMI Categories and Healthy BMI Ranges
The NHS BMI classification system divides adults into five distinct categories based on the BMI formula (weight in kg ÷ height in metres squared). Here are the standard UK BMI ranges:
- Underweight: BMI below 18.5 — may indicate insufficient energy reserves
- Healthy weight: BMI 18.5 to 24.9 — lowest risk for weight-related health conditions
- Overweight: BMI 25.0 to 29.9 — increased risk of health problems; modest lifestyle changes often recommended
- Obese (Class I): BMI 30.0 to 34.9 — significantly increased health risks
- Obese (Class II): BMI 35.0 to 39.9 — high health risks; medical support often recommended
- Severely obese (Class III): BMI 40.0 and above — very high risk; GP discussion strongly advised
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds within the overweight BMI range due to higher disease risk at lower BMI levels. A healthy BMI for these groups begins at 18.5 but extends only to 22.9, with overweight starting at 23.0.
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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.
BMI Limitations and Why Complementary Measures Matter
Whilst BMI classification is useful for population health screening, it has important limitations. BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat percentage. BMI also ignores where fat is stored; excess belly fat carries greater health risk than fat stored elsewhere. The BMI formula works less well for older adults (who naturally lose muscle), pregnant women, and very tall or very short individuals.
For a fuller health picture, your GP may also assess your waist circumference (increased risk above 94cm for men, 80cm for women) and overall cardiovascular fitness. Our free weight converter helps you track your weight across kg, stone, and pounds as you work towards a healthier range.
- 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 the healthy BMI range in the UK?
According to NHS guidelines, a healthy BMI for most UK adults is between 18.5 and 24.9. This range carries the lowest risk for weight-related diseases. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9 due to higher health risks at higher BMI levels. Use our BMI calculator to find your personal BMI quickly.
What BMI is considered overweight in the UK?
An overweight BMI classification in the UK starts at 25.0 and extends to 29.9. If your BMI falls in this range, your GP may suggest modest lifestyle changes including increased physical activity and dietary adjustments. The overweight BMI threshold is lower for people of South Asian heritage (23.0 and above).
At what BMI should I see my GP?
If your BMI classification shows you are in the obese range (30.0 or above), it's worth discussing with your GP, particularly if you have weight-related health conditions like high blood pressure or type 2 diabetes. Even at overweight BMI levels (25–29.9), a GP discussion is worthwhile if you have cardiovascular risk factors or family history concerns.
Why are BMI thresholds different for South Asian adults?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults develop type 2 diabetes and cardiovascular disease at lower BMI levels than European populations. The NHS therefore recommends lower BMI classification thresholds for these groups to reflect their individual health risk profile and enable earlier intervention.
Does BMI account for muscle mass?
No — the BMI formula does not distinguish between muscle and fat. This is a key BMI limitation. Very muscular individuals (including athletes) may have a higher BMI despite low body fat percentage. Your GP can discuss whether additional measurements like waist circumference or body composition assessment would be helpful.
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.