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
Who Is Obese — NHS BMI Categories Explained
In the UK, obesity is defined by BMI (body mass index) according to NHS guidelines. A person is considered obese if their BMI is 30 or above. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds due to higher health risks at lower BMI levels. Use our free BMI calculator above to check your personal BMI instantly and find out where you fall on the NHS scale.
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 — Overweight and Obese Thresholds
The NHS defines obesity using standardised BMI ranges that apply to all UK adults:
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese (Class III): BMI 40.0 and above
For South Asian, Chinese, Black African, and Black Caribbean adults, the thresholds are lower: overweight starts at BMI 23.0, and obesity starts at BMI 27.5. This is because these groups face higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. BMI is calculated by dividing weight in kilograms by height in metres squared. While useful as a screening tool, BMI doesn't account for muscle mass or fat distribution — your GP can provide personalised health advice based on your individual circumstances.
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 — A Complementary Health Check
Beyond BMI, waist circumference is an important health indicator. The NHS recommends checking your waist measurement as a complementary assessment of health risk:
- Men: Over 94cm (37 inches) = increased risk; over 102cm (40 inches) = high risk
- Women: Over 80cm (31.5 inches) = increased risk; over 88cm (34.5 inches) = high risk
A high waist measurement can indicate excess fat stored around internal organs, which increases risk of heart disease and type 2 diabetes even if BMI is in the healthy range. Use the weight converter on this page to check your weight in different units, then speak to your GP about your overall health profile — they can assess both BMI and waist measurement together to give you personalised guidance on 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 is the difference between overweight and obese according to NHS guidelines?
The NHS defines overweight as BMI 25.0–29.9 and obese as BMI 30.0 or above. Obesity is further divided into three classes based on increasing health risk. These categories help healthcare professionals assess weight-related health risks and recommend appropriate interventions.
Am I overweight if my BMI is 26?
Yes, according to NHS guidelines, a BMI of 26 falls in the overweight category (25.0–29.9). This doesn't mean you're unwell, but your GP may suggest lifestyle changes to reduce your risk of weight-related health conditions. Use our free BMI calculator above to see your personal BMI and healthy weight range.
Why are BMI thresholds lower for South Asian and Black African adults?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher risk of type 2 diabetes, cardiovascular disease, and other health conditions at the same BMI as white European adults. Lower thresholds (obesity from BMI 27.5 instead of 30) help identify health risk more accurately in these populations.
What does BMI not tell me about my health?
BMI doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. It also doesn't account for where fat is stored (central obesity is higher risk), age, or medical conditions. Waist measurement, fitness level, and medical history all matter alongside BMI. Your GP can give you a complete health picture.
What should I do if I'm obese?
Start by speaking to your GP, who can assess your individual health and discuss options. This may include lifestyle changes like diet and physical activity, NHS weight management programmes, or in some cases, prescription weight loss support. Our GLP-1 weight loss calculator can help you explore potential outcomes with medical support if your GP recommends it. ```
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.