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
What Is a BMI Must Score and How Is It Calculated?
Your BMI (Body Mass Index) is a single number that indicates whether your weight falls within a healthy range for your height. The "must score" refers to the baseline calculation itself — a simple mathematical formula used by the NHS and healthcare professionals across the UK to screen for weight-related health risks. Understanding your personal BMI score helps you and your GP assess whether your current weight poses any health concerns. Our free BMI calculator above will compute your exact score instantly using your height and weight in either metric or imperial measurements.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How the BMI Formula Works and What Your Score Means
The BMI formula is straightforward: divide your weight in kilograms by your height in metres squared (weight ÷ height²). For example, an adult weighing 75kg and 1.73m tall would have a BMI of approximately 25.1, which falls in the overweight category according to NHS guidelines.
Once calculated, your BMI score is placed into one of these NHS BMI categories:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9 (this is the healthy BMI range for most UK adults)
- Overweight: BMI 25.0–29.9
- Obese Class I: BMI 30.0–34.9
- Obese Class II: BMI 35.0–39.9
- Severely obese: BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI thresholds are lower due to higher health risks at these weights. The healthy range begins at 18.5 but ends at 22.9 instead of 24.9, and overweight begins 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.
Understanding BMI Limitations and Complementary Measures
Although your BMI must score is useful, it has important limitations. BMI does not distinguish between muscle and fat — athletes or very muscular individuals may have a high BMI but excellent health. BMI also ignores where fat is stored; excess fat around the abdomen carries greater health risk than fat elsewhere on the body.
For a more complete picture, your GP may also measure your waist circumference. The NHS recommends a healthy waist measurement of under 94cm (37 inches) for men and under 80cm (31.5 inches) for women. Combined with your BMI score, this gives a much better assessment of your actual health risk. Use our weight converter to check your weight in different units, and discuss your personal BMI results with your GP for tailored health advice.
- 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 difference between BMI and body fat percentage?
BMI is a screening tool based only on height and weight, while body fat percentage measures the actual proportion of fat in your body. Two people with identical BMI scores may have very different body compositions — one might be muscular, the other not. Body fat percentage is more accurate but requires specialist equipment to measure.
Can my BMI score change if I don't change my weight?
No. Your BMI is purely a calculation based on your weight and height. If your weight and height remain the same, your BMI will remain the same. It will only change if your weight changes or — very rarely — if you're still growing taller (in younger people).
Is a BMI of 25 considered overweight in the UK?
Yes. According to NHS guidelines, a BMI of 25.0 or higher is classified as overweight. The healthy BMI range is 18.5–24.9. However, for South Asian and other specific ethnic groups, the overweight threshold starts at BMI 23.0.
Why do South Asian adults have different BMI thresholds?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults have a higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS therefore recommends lower BMI thresholds for these groups to identify health risks earlier and enable earlier intervention.
What should I do if my BMI is in the overweight category?
Start by discussing your result with your GP, who can assess your individual health context. Small lifestyle changes — such as increasing physical activity and adjusting your diet — can help. Your GP may also discuss weight management options if appropriate. Use our free BMI calculator and progress tracker to monitor changes over time.
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.