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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Understanding Weight Equations in UK Health Guidance
A weight equation is a mathematical formula used to assess your health based on your weight, height, and other measurements. In the UK, the most common weight equation is the BMI (Body Mass Index) formula, which helps your GP and NHS health professionals determine whether your weight falls into a healthy range. Understanding these equations gives you insight into your own health metrics and can guide conversations with your healthcare provider about weight management.
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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.
Common Weight Equations Used in UK Health Guidance
The BMI equation is the primary weight equation used by the NHS. The formula is: BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75 metres tall, your BMI would be 70 ÷ (1.75)² = 22.9, which falls in the healthy weight range of 18.5 to 24.9 according to NHS guidance. The NHS also recognises waist-to-height ratio, calculated as waist circumference ÷ height (using the same units). A healthy ratio is below 0.5 for all UK adults. This equation is considered more accurate than BMI alone because it accounts for where fat is stored, which is important for assessing cardiovascular risk. Our free BMI calculator above instantly calculates your BMI and shows you where you fall on the NHS health scale, taking into account ethnicity-adjusted thresholds for South Asian, Chinese, Black African, and Black Caribbean adults.
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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.
Using Weight Equations for Healthy Weight Management
Once you know your weight equation results, use them to set realistic health goals. The NHS recommends sustainable weight loss of 0.5 to 1 kg per week, which requires a calorie deficit of approximately 500 kcal per day. You can calculate your ideal weight range using the healthy BMI bounds: multiply your height (in metres) squared by 18.5 (lower bound) and 24.9 (upper bound). For example, at 1.75m, a healthy weight range is 56–76 kg. If you're considering weight management support, including prescription options like GLP-1 medications, try our GLP-1 weight loss calculator to explore potential outcomes. Always discuss your personal weight health with your GP, who can assess your individual circumstances and recommend the best approach for you.
- 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 the BMI weight equation tell me?
BMI (Body Mass Index) is a screening tool that estimates whether your weight is healthy for your height. It divides your weight in kg by your height in metres squared. The NHS uses BMI categories: under 18.5 is underweight, 18.5–24.9 is healthy weight, 25–29.9 is overweight, and 30+ is obese. However, BMI has limitations—it doesn't account for muscle mass or where fat is stored, so your GP may consider other factors too.
Why does the NHS use weight equations?
Weight equations like BMI help the NHS and GPs quickly assess health risk at population and individual levels. They're simple, consistent, and evidence-based screening tools. They help identify who may benefit from weight management support, lifestyle changes, or further health assessments. Combined with other measurements like waist circumference, they give a more complete picture of your health.
Are there different weight equations for different ethnic groups?
Yes. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups face higher health risks at lower BMI levels. For these groups, healthy weight is 18.5–22.9, and overweight begins at 23. Our BMI calculator accounts for these differences automatically.
How do I calculate my healthy weight range using the BMI equation?
Multiply your height (in metres) by itself, then multiply by 18.5 (lower bound) and 24.9 (upper bound). For example, at 1.75m: lower bound = 18.5 × (1.75)² = 56.6 kg; upper bound = 24.9 × (1.75)² = 76.2 kg. Use our free BMI calculator above for gradual improvement and to see your personal healthy weight range.
What should I do if my weight equation results show I'm overweight or obese?
Speak to your GP for personalised advice. They can assess your individual health, discuss lifestyle changes, and determine if weight management support—such as diet, exercise programmes, or prescription options—is appropriate for you. The NHS offers tier 1–4 weight management pathways depending on your needs and local availability.
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.