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 Body Index Score and How Does It Work?
A body index score is a health measurement that assesses your weight in relation to your height, similar to BMI but often used as part of a broader health evaluation. In the UK, NHS guidance focuses primarily on BMI as the standard screening tool, though body composition analysis and other metrics are increasingly recognised as important alongside traditional weight measurements. Understanding your body index score can help you make informed decisions about your health and whether you might benefit from speaking with your GP about weight management support.
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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.
Body Index Score vs BMI: Understanding the Difference
The term "body index score" is sometimes used interchangeably with BMI (body mass index), but healthcare professionals may also use it to describe broader assessments of body composition and health risk. BMI remains the standard UK health metric recommended by the NHS and NICE for screening overweight and obesity in adults.
BMI is calculated as weight (kg) divided by height squared (m²). The NHS healthy weight ranges are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obese (30.0 and above). However, BMI has important limitations — it does not distinguish between muscle and fat, and does not account for where fat is stored on your body.
- BMI provides a quick screening tool for population-level health risk
- Waist circumference measurements add important context to BMI
- Body composition analysis (muscle vs fat percentage) is increasingly used in clinical practice
- For South Asian, Chinese, Black African, and Black Caribbean populations, lower BMI thresholds apply due to higher health risks at lower weights
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Using Body Index Assessment in Your UK Health Journey
If you're concerned about your weight or overall health, your GP can help you understand what your body index score or BMI means for you personally. Use our free BMI calculator above to check your BMI instantly and see where you fall within NHS healthy weight ranges.
Beyond numbers, NHS weight management guidance emphasises sustainable lifestyle changes: a balanced diet, regular physical activity, and adequate sleep. If you're interested in weight loss support, our weight converter tool can help you track progress in your preferred units (stone, kg, or lbs), and the GLP-1 weight loss calculator can help you understand medication options if your GP recommends them. Always discuss any health concerns or weight management plans with your GP or a qualified healthcare professional.
- 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.
Is body index score the same as BMI?
The terms are often used similarly, but body index score can refer to a broader health assessment including BMI, waist circumference, and body composition. BMI (body mass index) is the standard NHS screening tool. Both measure weight relative to height, but healthcare professionals may look at additional factors for a complete picture of your health.
What is a healthy body index score in the UK?
According to NHS guidance, a healthy BMI is between 18.5 and 24.9. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds (18.5–22.9) because these populations face higher health risks at lower BMI levels. Your GP can advise what's healthy for you individually.
Why does body index score matter for my health?
A body index score or BMI helps identify health risks related to excess weight, including type 2 diabetes, heart disease, and high blood pressure. However, it's just one screening tool. Waist circumference and overall fitness also matter. Regular health checks with your GP provide the best personalised guidance.
Can body index score be inaccurate?
Yes, body index score (or BMI) doesn't account for muscle mass, bone density, or where fat is stored. Athletes may have high BMI but low body fat. It's less accurate for elderly people, children, and during pregnancy. That's why healthcare professionals often look at additional measurements alongside BMI.
How can I track changes in my body index score?
Use our free progress tracker to log your weight regularly in stone, kg, or lbs — whichever you prefer. Combined with our BMI calculator, you can monitor how your body index score changes over time. Track alongside waist measurements and how you feel for a fuller picture of your health progress.
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.