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 An Obese BMI?
An obese BMI according to NHS guidelines is a BMI of 30 kg/m² or above. This measurement indicates excess body weight that may increase risk of health conditions including type 2 diabetes, heart disease, and high blood pressure. However, BMI is just one health screening tool — it doesn't account for muscle mass, where fat is stored, or your overall fitness level. Use our free BMI calculator above to check your personal BMI instantly and understand where you fall within the NHS BMI range for your height and weight.
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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.
NHS BMI Categories and Obese Ranges
The NHS BMI formula divides weight in kilograms by height in metres squared (kg/m²). The healthy BMI range for UK adults is 18.5 to 24.9, while overweight falls between 25.0 and 29.9. Obesity is then divided into three classes:
- Class I (Obese): BMI 30.0–34.9
- Class II (Obese): BMI 35.0–39.9
- Class III (Severely Obese): BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI categories UK-specific thresholds because these populations face higher health risks at lower BMI levels. For these groups, a healthy BMI is 18.5–22.9, overweight is 23.0–27.4, and obese starts at 27.5. Understanding your specific obese BMI threshold based on your ethnicity and health profile is important for personalised health planning.
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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.
BMI Limitations and Complementary Health Measures
BMI limitations are significant and worth understanding. BMI does not distinguish between muscle and fat — athletes or very muscular individuals may have a high BMI but low body fat percentage. It also doesn't account for where fat is stored around your body, which matters for health risk. Age, bone density, and pregnancy all affect BMI accuracy. That's why your GP may also assess waist circumference: men over 94cm (37 inches) have increased risk, while women over 80cm (31.5 inches) do. A comprehensive health check includes blood pressure, cholesterol levels, blood sugar, and fitness — not just BMI. If you're concerned about your weight and health, speak to your GP about personalised advice tailored to your individual circumstances.
- 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 number is considered obese?
According to NHS guidelines, an obese BMI starts at 30 kg/m² and above. This is divided into three classes: Class I (30–34.9), Class II (35–39.9), and Class III or severely obese (40 and above). For certain ethnic groups, lower thresholds apply — your GP can advise on your personal risk.
How is BMI calculated?
BMI is calculated using the formula: weight in kilograms divided by height in metres squared (kg/m²). For example, a person weighing 90kg who is 1.75 metres tall has a BMI of 29.4. Use our free BMI calculator above for gradual improvement based on your measurements.
Is a BMI of 30 definitely obese?
A BMI of 30 falls into the obese category according to NHS definitions. However, BMI is a screening tool and doesn't tell the whole story — muscle mass, fitness level, where fat is stored, and overall health all matter. Your GP can assess whether your specific BMI indicates a health concern for you personally.
What health risks come with an obese BMI?
An obese BMI increases risk of type 2 diabetes, heart disease, stroke, high blood pressure, certain cancers, sleep apnoea, and joint problems. However, losing even 5–10% of body weight can significantly improve these risk factors. Your GP can advise on safe, sustainable approaches tailored to your health.
How can I check my BMI and healthy weight range?
Use our free BMI calculator on this page — enter your weight in stone/kg and height in feet/cm, and it instantly shows your BMI and healthy weight range for your height. You can also use our weight converter to switch between different units for clarity.
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.