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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How To Find the BMI Equation — NHS Context
Understanding the BMI formula is straightforward, and the NHS uses the same equation across all UK health services. BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. Whether you're checking your own BMI or trying to understand NHS health guidance, knowing the basic BMI range and how to apply the formula helps you interpret your personal health context. This guide explains the equation, NHS BMI categories, and what healthy weight means according to UK healthcare standards.
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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.
The BMI Formula and NHS Categories
The BMI formula is: BMI = weight (kg) ÷ height (m)²
For example, if you weigh 70kg and are 1.75 metres tall: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9
The NHS uses five standard BMI categories for adults:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25.0–29.9: Overweight
- 30.0–34.9: Obese (Class I)
- 35.0–39.9: Obese (Class II)
- 40.0+: Severely obese (Class III)
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds: healthy weight is 18.5–22.9, and overweight starts at 23.0. Use our free BMI calculator above to find your personal BMI instantly.
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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.
NHS Weight Management and When To Seek Help
The NHS recognises that BMI has limitations—it doesn't account for muscle mass, bone density, or where fat is stored. However, BMI remains the standard screening tool across NHS services. If your BMI falls outside the healthy range, your GP can provide personalised advice about your health risks and options.
The NHS weight management pathway includes: tier 1 (self-help and community programmes), tier 2 (primary care support), tier 3 (specialist services where medications like GLP-1 injections may be considered), and tier 4 (bariatric surgery for severe obesity). Your GP is your first point of contact—they can assess your individual health and recommend the appropriate tier of support.
- 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's the difference between the BMI formula and BMI chart?
The BMI formula (weight in kg ÷ height in m²) calculates your exact number. An NHS BMI chart visually shows where your BMI falls in the healthy, overweight, or obese categories. Both show the same information—the formula is more precise, the chart is easier to read at a glance.
Does the BMI equation work the same for men and women?
Yes. The BMI formula is identical for all adults regardless of sex. However, average body composition differs—men typically have more muscle, women more fat. BMI doesn't distinguish between them, which is one reason why BMI has limitations despite being NHS-standard.
Can I use the BMI formula with stone and pounds instead of kilograms?
The standard NHS BMI formula uses kilograms and metres. You can use an imperial approximation (weight in lbs × 703 ÷ height in inches²), but it's easier to convert your weight to kg first. Use our weight converter above to switch between stone, pounds, and kilograms instantly.
What BMI range does the NHS consider healthy?
According to NHS guidance, a healthy BMI for most UK adults is 18.5–24.9. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends 18.5–22.9. Your GP can advise if your individual BMI requires action.
Is there a different BMI equation for children?
Children don't use the adult BMI formula. Instead, the NHS uses age and sex-specific growth charts (UK90 reference). If you're checking a child's weight, always consult your GP or use the NHS Healthy Weight Calculator for children rather than the adult equation.
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.