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 Index Calc in UK Health?
Index calc refers to health indexing calculations — tools that measure and interpret body weight, health metrics, and wellness indicators. In the UK, the most common index calc is the Body Mass Index (BMI), which healthcare professionals and patients use to assess whether weight falls within a healthy range according to NHS guidance. MyWeightCheck provides free index calc tools aligned with UK health standards, including BMI calculators, weight converters, and health trackers to help you understand your personal health metrics in context.
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.
Common Health Index Calculations in the UK
Body Mass Index (BMI) is the primary index calc used by the NHS. It divides your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). NHS guidelines define a healthy BMI as 18.5 to 24.9, though for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9.
Waist-to-height ratio is another useful index calc that measures cardiovascular risk. A ratio below 0.5 is considered healthy for all adults. This measurement sometimes provides better health risk prediction than BMI alone, as it accounts for fat distribution.
- Use our free BMI calculator above to check your personal BMI instantly and see which NHS category you fall into
- Convert your weight between kg, stone, and lbs using our weight converter for UK-standard measurements
- Your GP can interpret your index calc results in the context of your overall health history
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.
How Index Calc Supports Weight Management
Index calc tools help establish baseline health metrics and track progress over time. If you're considering weight management options — whether through lifestyle changes, NHS programmes, or prescription treatments like GLP-1 medications (Mounjaro or Wegovy) — understanding your current index calc provides essential context.
Our GLP-1 weight loss calculator can help you estimate potential weight loss and how your index calc metrics might change with treatment. Regular tracking using index calc allows you and your healthcare team to monitor whether interventions are working and adjust plans accordingly. Weight management is most effective when supported by reliable measurements and professional guidance.
- 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 does index calc mean in NHS health guidance?
Index calc refers to calculated health metrics like BMI, waist-to-height ratio, and other wellness indices. The NHS primarily uses BMI as a screening tool to assess weight categories and related health risks. Your GP can explain what your personal index calc results mean for your health.
Is BMI the only index calc that matters?
No. While BMI is widely used, it has limitations — it doesn't distinguish between muscle and fat, or account for fat distribution. Waist circumference, waist-to-height ratio, and body composition are also important. A holistic assessment considers multiple measurements alongside your individual health history.
How often should I check my index calc?
For general health monitoring, checking your BMI or weight quarterly is reasonable. If you're actively losing weight, monthly tracking using our free progress tracker can help you stay motivated. Your GP may recommend more frequent checks if you have weight-related health conditions.
Can index calc predict my health risk?
Index calc tools like BMI help identify general risk categories, but they're screening tools, not diagnostic. Your actual health risk depends on genetics, lifestyle, medical history, and multiple other factors. Your GP provides personalised risk assessment based on your complete health picture.
How do Mounjaro or Wegovy affect my index calc?
These GLP-1 medications may support weight loss alongside diet and activity changes, which would improve your index calc metrics over time. Individual results vary — our GLP-1 calculator can help you understand potential changes. Any medication requires prescription and clinical assessment from a healthcare professional.
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.