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
What Is Classed As Obese in the UK?
In the UK, obesity is defined by your BMI (body mass index) rather than weight alone. According to NHS guidelines, you are classed as obese if your BMI is 30 or above. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower threshold of 27.5 or above due to higher health risks at lower BMI levels. Obesity increases your risk of serious health conditions including type 2 diabetes, heart disease, and certain cancers. Use our free BMI calculator above to check your personal BMI and see where you fall on the NHS scale right now.
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.
NHS BMI Categories and Obesity Thresholds
The NHS uses a standardised BMI scale to classify weight status for all UK adults. Your BMI is calculated by dividing your weight in kilograms by your height in metres squared. Here are the official NHS BMI categories:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9 — this is the overweight bmi threshold where health risks begin to increase
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
If your BMI falls into the obese category (30 or above), your GP may recommend lifestyle changes, weight monitoring, or in some cases, prescription weight management support. Even modest weight loss of 5–10% can significantly improve your health outcomes and reduce disease risk.
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.
Waist Measurement and Health Risk
BMI is a useful screening tool, but it doesn't account for where fat is stored on your body. Waist measurement is an important complementary check — excess fat around your stomach carries greater health risk than fat elsewhere. The NHS recommends:
- Men: waist over 94cm (37in) indicates increased risk; over 102cm (40in) indicates high risk
- Women: waist over 80cm (31.5in) indicates increased risk; over 88cm (34.5in) indicates high risk
If you're in the overweight or obese BMI range and have a large waist measurement, speak to your GP about weight management options. Our BMI calculator and weight converter tools help you track your measurements and progress in the units that suit you best.
- 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.
Am I overweight or obese?
You're overweight if your BMI is 25.0–29.9, and obese if your BMI is 30 or above according to NHS guidelines. Use our free BMI calculator above to find your exact BMI. For people of South Asian, Black African, or Black Caribbean heritage, lower thresholds apply (27.5+). Your GP can also assess your individual health risk.
What's the difference between overweight and obese BMI?
Overweight BMI (25–29.9) means increased health risk, but obese BMI (30+) indicates significantly higher risk of type 2 diabetes, heart disease, and other conditions. Obese is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+). Each category suggests different health management approaches.
Can I be obese without being overweight?
No — obese BMI is always higher than overweight BMI. However, you can have a healthy BMI and still have excess body fat if you carry little muscle mass. BMI doesn't distinguish between muscle and fat. Waist measurement and body composition are also important health indicators alongside BMI.
What health risks come with obesity?
Obesity significantly increases risk of type 2 diabetes, high blood pressure, heart disease, stroke, certain cancers, sleep apnoea, and joint problems. The NHS estimates obesity contributes to approximately 1 in 13 deaths in the UK. Even losing 5–10% of your body weight can meaningfully reduce these risks.
What should I do if I'm classed as obese?
Start by speaking to your GP, who can assess your individual health and discuss options. These may include lifestyle changes (diet and exercise), structured NHS weight management programmes, or prescription weight loss support. Use our free BMI calculator and progress tracker to monitor your journey and stay motivated.
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.