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
Am I Obese? Use Our Free BMI Calculator to Check
If you're wondering whether you're obese, the quickest way to find out is by checking your BMI using our free calculator above. Obesity in the UK is defined as a BMI of 30 or above according to NHS guidelines. However, BMI is just one measure of health — waist circumference and overall fitness also matter. This guide explains NHS BMI categories, what your results mean, and what to do next if you want to improve your health.
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 defines obesity based on BMI measurements. BMI (body mass index) is calculated by dividing your weight in kilograms by your height in metres squared. Our free BMI calculator above does this instantly — simply enter your weight and height.
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- 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 you have a BMI of 30 or above, you fall into the obese category. However, it's important to understand that BMI doesn't account for muscle mass, bone density, or where fat is stored on your body. Athletes or very muscular individuals may have a higher BMI but lower body fat. Your GP can provide personalised advice about what your BMI means for your individual health.
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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.
Waist Measurement and What to Do Next
Beyond BMI, waist circumference is an important health marker. The NHS recommends checking where your fat is stored, as excess belly fat carries greater health risks. Men should aim for a waist measurement under 94 cm (37 inches), and women under 80 cm (31.5 inches). Measurements above these thresholds suggest increased health risk even at lower BMI levels.
If you're overweight or obese, small changes can help. The NHS recommends losing weight at 0.5 to 1 kg per week through a balanced diet and increased physical activity. If you're struggling, your GP can refer you to local weight management services or discuss treatment options. Use our free progress tracker to monitor your 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's the difference between overweight and obese?
Overweight is a BMI of 25.0 to 29.9, while obese starts at BMI 30.0. Both indicate excess body weight, but obese categories represent higher health risk. The NHS recommends consulting your GP if you're in either category to discuss your individual health.
Can I be healthy with a BMI in the obese range?
BMI is a screening tool, not a diagnostic measure. Some people with higher BMI may be healthy, particularly if they're very muscular. However, obesity is statistically linked to type 2 diabetes, heart disease, and other conditions. Your GP can assess your overall health beyond BMI alone.
What should I do if my BMI shows I'm obese?
Start by speaking with your GP, who can assess your health and discuss options. Small lifestyle changes — like reducing calories by 500 per day and increasing activity — can help. Your GP may refer you to NHS weight management services or discuss prescription options if appropriate.
Do ethnicity-adjusted BMI thresholds apply to me?
Yes. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, and Black Caribbean heritage due to higher health risks at lower BMI levels. If you're from these backgrounds, discuss your specific thresholds with your GP.
Is waist measurement as important as BMI?
Both matter. BMI tells you if you're carrying excess weight overall, while waist measurement reveals where fat is stored. Excess belly fat carries greater health risks. Ideally, both measures should be within healthy ranges. Our free BMI calculator helps with the first step — discuss waist measurement with your GP.
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.