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
Understanding NHS Obesity and Health Risks
Obesity is a significant health concern in the UK, affecting around 28% of UK adults. The NHS defines obesity as a BMI of 30 or above, though lower thresholds apply for people of South Asian, Chinese, Black African, and Black Caribbean heritage. Being overweight or obese increases the risk of serious health conditions and complications. Understanding these risks and the support available through the NHS can help you make informed decisions about your health and wellbeing.
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.
Health Conditions Linked to Excess Weight
Carrying excess weight significantly increases your risk of developing serious health conditions. Type 2 diabetes is the most common complication—individuals with obesity have up to 80 times higher risk compared to those at a healthy weight. Cardiovascular disease including heart attack and stroke is strongly linked to obesity, as excess weight increases blood pressure and cholesterol levels.
Other obesity-related conditions include:
- Obstructive sleep apnoea—disrupted breathing during sleep affecting energy and health
- Osteoarthritis—joint damage and chronic pain, especially in knees and hips
- Non-alcoholic fatty liver disease—liver damage without alcohol use
- 13 cancer types—including breast, bowel, and endometrial cancers
- Fertility problems—affecting both men and women
Even modest weight loss of 5–10% of body weight can significantly reduce these health risks and improve your health markers. Use our free BMI calculator above to check your personal BMI and healthy weight range.
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.
NHS Support and Weight Management Options
The NHS offers a structured pathway for weight management support. Tier 1 includes self-help tools and community programmes—starting point for most adults. Your GP can assess your health and may refer you to Tier 3 specialist weight management services if you meet eligibility criteria (typically BMI 30+ or 27+ with weight-related health conditions).
For eligible adults, the NHS may now prescribe weight management medications like tirzepatide (Mounjaro) or semaglutide (Wegovy) alongside lifestyle support. These are prescription-only and require clinical assessment. Lifestyle changes—reduced-calorie diet and increased physical activity—remain the foundation of sustainable weight loss. Our free GLP-1 weight loss calculator can help project potential outcomes, and our weight converter helps you understand your weight in UK measurements (stone, lbs, kg).
- 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 is the NHS obesity threshold in the UK?
The NHS defines obesity as a BMI of 30 or above for most UK adults. However, people of South Asian, Chinese, Black African, or Black Caribbean heritage have lower thresholds starting at BMI 27.5+, as these groups face higher health risks at lower weights. Use our BMI calculator to find your personal threshold.
How much does obesity cost the NHS annually?
Obesity costs the NHS approximately £6.5 billion per year in treatment and care. This includes managing weight-related conditions like diabetes, heart disease, and joint problems. Early intervention and weight management can reduce these costs significantly.
Can the NHS prescribe weight loss injections?
Yes, the NHS now prescribes weight loss medications like tirzepatide (Mounjaro) and semaglutide (Wegovy) through specialist Tier 3 weight management services. You must meet eligibility criteria and be referred by your GP. Access varies by region and waiting times can be lengthy.
What is the healthiest rate of weight loss according to the NHS?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week for sustainable, healthy weight loss. This typically requires a calorie deficit of around 500 calories per day. Faster weight loss increases risk of muscle loss and nutritional deficiency.
What lifestyle changes does the NHS recommend for weight management?
The NHS recommends combining dietary changes (reducing calories, eating whole foods) with increased physical activity (150 minutes moderate exercise weekly). Your GP or a Tier 2 weight management programme can provide personalised guidance. Track your progress using our free progress tracker.
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.