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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Am I Obese? Check Your Weight Status in the UK
Obesity in the UK is defined by NHS guidelines using Body Mass Index (BMI). If you're wondering whether you're overweight or obese, our free BMI calculator above can help you find out instantly. The NHS classifies BMI 30 and above as obese, while BMI 25–29.9 is overweight. Your BMI depends on your weight and height, and knowing where you fall is an important first step toward understanding your health. This guide explains the NHS BMI categories and what they mean for you.
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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.
Understanding NHS BMI Categories and Obesity Thresholds
The NHS defines obesity as a BMI of 30 or above. This classification helps healthcare professionals assess health risk and plan appropriate support. Here are the key NHS BMI categories:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25–29.9
- Obese (Class I): BMI 30–34.9
- Obese (Class II): BMI 35–39.9
- Severely obese (Class III): BMI 40 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds. For these groups, a healthy BMI is 18.5–22.9, overweight is 23–27.4, and obese is 27.5 and above. This is because these populations face higher health risks at lower BMI levels. Use our free BMI calculator above to determine your personal BMI and where you fall within these NHS guidelines.
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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.
Why Waist Measurement Matters — Beyond BMI
BMI alone doesn't tell the whole story. Waist circumference is equally important because where you carry weight affects health risk. The NHS recommends measuring waist circumference as a complementary health check. For men, a waist over 94cm (37 inches) indicates increased risk, and over 102cm (40 inches) indicates high risk. For women, over 80cm (31.5 inches) shows increased risk, and over 88cm (34.5 inches) shows high risk. Even if your BMI is in the healthy range, a large waist circumference may suggest central obesity. Combining your BMI result with a waist measurement gives you a more complete picture of your health status. If you're concerned about your weight or health, speak to your GP who can provide personalised advice and discuss next steps.
- 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 in the UK?
The NHS defines obese as a BMI of 30 or above. This is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+). However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower threshold — obese is 27.5 and above for these groups.
How is my BMI calculated?
BMI is calculated as weight (kg) divided by height (metres) squared. For example, at 1.73m tall, a person weighing 95kg would have a BMI of about 31.8. Our free BMI calculator above works this out instantly — just enter your weight and height in your preferred units (kg, stone, or lbs).
Is being overweight the same as being obese?
No. The NHS defines overweight as BMI 25–29.9, and obese as BMI 30 or above. Overweight means your weight is above the healthy range, but obesity indicates a higher health risk category. Both can benefit from lifestyle changes, and your GP can advise on personalised support.
Should I only use BMI to check my health?
BMI is a useful screening tool, but it has limitations — it doesn't distinguish between muscle and fat, and doesn't account for where weight is stored. That's why the NHS recommends combining BMI with waist measurement. Both together give a more accurate picture of your health risk.
What should I do if I'm overweight or obese?
Speak to your GP. The NHS offers support through its weight management pathway, starting with tier 1 self-help and community programmes. For significant obesity, specialist tier 3 services may be available. Your GP can also assess whether prescription weight loss treatment might be appropriate for you. 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.