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 Obesity and Health — A UK Guide
If you're concerned about your weight and health, you're not alone. In the UK, around 28% of adults live with obesity, and excess weight can affect your overall wellbeing. Understanding how weight relates to health — and what support is available — is an important first step. This guide covers the health context of obesity, what the NHS says, and practical options to help you move towards a healthier weight if you choose to.
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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
Excess weight can increase the risk of several health conditions. According to NHS and Public Health England data, obesity is linked to:
- Type 2 diabetes: Risk increases significantly with weight; at severe obesity, risk can be up to 80 times higher than for people with a healthy weight
- High blood pressure (hypertension): Extra weight puts strain on the heart and blood vessels
- Heart disease and stroke: Obesity increases cardiovascular risk substantially
- Certain cancers: 13 types of cancer are linked to excess weight, including breast, bowel, and endometrial cancer
- Sleep apnoea: Can cause interrupted sleep and breathing problems
- Osteoarthritis: Extra weight puts pressure on joints, particularly knees and hips
- Non-alcoholic fatty liver disease (NAFLD): Fat accumulation in the liver
Even modest weight loss — as little as 5–10% of body weight — can reduce these risks meaningfully. Use our free BMI calculator above to check your personal BMI and understand where you sit on the NHS health scale.
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 recognises that sustainable weight loss requires personalised support. If you're interested in managing your weight, your GP can discuss options tailored to your circumstances. The NHS pathway includes tier 1 (self-help and digital tools), tier 2 (behaviour change programmes), tier 3 (specialist weight management services), and tier 4 (bariatric surgery for severe cases).
For eligible adults — those with a BMI of 30 or above, or 27 or above with weight-related health conditions — prescription weight loss medications may be an option through specialist NHS services or private assessment. Try our GLP-1 weight loss calculator to explore potential outcomes if you're considering medication. Remember, sustainable weight loss combines medication (if prescribed), dietary changes, and increased physical activity. Your GP is the best starting point for personalised advice.
- 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 counts as obese?
According to NHS guidelines, obesity is defined as a BMI of 30 or above. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds starting at BMI 27.5 due to higher health risks at lower BMI levels. Use our free BMI calculator to check your personal BMI.
Is obesity purely about weight?
No. Obesity involves excess body fat, but weight alone doesn't tell the full story. BMI is a screening tool but doesn't account for muscle mass or where fat is stored. Waist circumference is also important — for men, over 102cm (40in) indicates high health risk; for women, over 88cm (34.5in) indicates high risk.
Can weight-related health conditions improve with weight loss?
Yes. Evidence shows that losing 5–10% of body weight can meaningfully reduce blood pressure, improve blood sugar control, lower cholesterol, reduce sleep apnoea severity, ease joint pain, and lower cancer risk. Even modest, sustainable weight loss has measurable health benefits.
What's the safest rate of weight loss?
The NHS recommends losing no more than 0.5–1kg (1–2lbs) per week for sustainable results. This rate helps preserve muscle and is more likely to lead to lasting change. Faster weight loss may lead to greater muscle loss and is not recommended without medical supervision.
Are weight loss medications available on the NHS?
Prescription weight loss medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) are available through NHS specialist tier 3 weight management services for eligible adults. Availability and waiting times vary significantly by region. Your GP can discuss referral options and what's available in your area.
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.