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
How Is Obesity Calculated in the UK?
Obesity is primarily calculated using Body Mass Index (BMI), a measurement based on your weight and height. In the UK, the NHS uses standardised BMI categories to assess whether someone may be at increased health risk due to excess weight. Understanding how obesity is calculated helps you know whether you fall into the obese category and what health support might be available to you. The calculation is straightforward, but it's important to recognise that BMI is just one screening tool—your overall health involves many factors.
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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.
Health Conditions Linked to Excess Weight
Being classified as obese significantly increases your risk of developing serious health conditions. Research shows that excess weight contributes to approximately 1 in 13 deaths in the UK.
- Type 2 diabetes: Obesity increases risk by up to 80 times compared to people at a healthy weight
- Heart disease and stroke: Excess weight raises blood pressure and cholesterol, straining the cardiovascular system
- Certain cancers: The NHS links overweight and obesity to 13 types of cancer, including bowel, breast, and liver cancer
- Obstructive sleep apnoea: Excess weight narrows airways, disrupting sleep quality
- Joint problems: Extra weight places pressure on knees, hips, and ankles, increasing arthritis risk
- Non-alcoholic fatty liver disease: Fat accumulation in the liver can lead to serious liver damage
The good news is that even a 5–10% reduction in body weight can significantly improve these conditions and reduce health risks.
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.
Support Available on the NHS and Beyond
If you're classified as obese, support is available through the NHS weight management pathway. Start by speaking with your GP, who can assess your health and refer you to appropriate services. You can check your personal obesity risk using our free BMI calculator above.
For eligible adults, the NHS offers tier 3 specialist weight management services, which may include dietary support, physical activity programmes, and prescription weight loss medications like Mounjaro or Wegovy. Private options are also available through GPhC-registered services. Sustainable weight loss combines dietary changes, increased activity, and—where appropriate—medical support. Our free progress tracker can help you log your weight loss journey.
- 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 BMI is considered obese in the UK?
According to NHS guidelines, a BMI of 30.0 or above is classified as obese. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, a BMI of 27.5 or above is considered obese due to higher health risks at lower BMI levels in these populations.
How do I calculate my obesity BMI myself?
Use the formula: BMI = weight (kg) ÷ height (m)². For example, someone weighing 85kg and 1.75m tall would have a BMI of 27.8. Use our free BMI calculator on this page for instant, accurate results—it also shows you exactly where you fall on the NHS health scale.
Can I lose weight through NHS support?
Yes. Start with your GP, who can refer you to tier 3 specialist weight management services. These services offer behaviour change support, dietary advice, physical activity programmes, and potentially prescription weight loss medications if you're eligible. Waiting times vary by region, but support is available.
What if my BMI is just above the obese threshold?
Even if your BMI is just over 30, reducing weight by just 5–10% can improve blood sugar control, blood pressure, and cholesterol. This modest weight loss often has significant health benefits and reduces the risk of serious conditions. Speak with your GP about realistic, sustainable targets.
Are prescription weight loss medications available on the NHS?
Yes, medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) are available through NHS tier 3 specialist weight management services for eligible adults. Access varies by region and availability. Private prescription is also an option following an online clinical assessment. Individual eligibility is assessed by a prescriber.
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.