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 Adult BMI and What Does It Mean?
Adult BMI (Body Mass Index) is a health screening tool that measures body weight relative to height. It helps determine whether an adult falls into a healthy weight range according to NHS guidelines. Your BMI is calculated by dividing your weight in kilograms by your height in metres squared. While BMI is a useful starting point for understanding weight-related health risks, it's important to understand what it measures and its limitations. Use our free BMI calculator above to find your personal BMI instantly and see where you fall on the NHS scale.
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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 Healthy Weight Ranges
The NHS BMI formula divides your weight (kg) by your height (m) squared. According to NHS guidelines, adult BMI categories are:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight (the target healthy BMI range for most adults)
- 25.0–29.9: Overweight
- 30.0–34.9: Obese (Class I)
- 35.0–39.9: Obese (Class II)
- 40.0 and above: Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI thresholds are lower due to higher health risks at lower weights. For these groups, a healthy weight starts at 18.5 and overweight begins at 23.0. If you're unsure which BMI range UK applies to you, speak to your GP. Our free BMI calculator can help you determine your personal category instantly.
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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.
BMI Limitations and Complementary Health Measures
While BMI is useful, it has important BMI limitations. It doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. BMI also doesn't account for where fat is stored, which matters for health risk. Age, bone density, and ethnicity all affect what BMI means for an individual.
The NHS recommends combining BMI with waist circumference measurement: over 94cm (37 inches) for men or 80cm (31.5 inches) for women suggests increased health risk. Body fat percentage and fitness level are also important. Your GP can provide personalised advice about your weight and health beyond BMI alone. Use our free weight converter to track your weight in both metric and imperial units as part of your health monitoring.
- 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.
How do I calculate my adult BMI?
Divide your weight in kilograms by your height in metres squared. For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = BMI of 22.9 (healthy range). Use our free BMI calculator above for gradual improvement across all measurements.
What's the healthy BMI range for UK adults?
According to NHS guidelines, a healthy BMI is between 18.5 and 24.9 for most adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9. Your GP can advise on your personal healthy weight target.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It doesn't distinguish muscle from fat, doesn't account for age or bone density, and doesn't show fat distribution. For a complete health picture, combine BMI with waist circumference, fitness level, and GP advice.
What should I do if my BMI is outside the healthy range?
Speak to your GP who can assess your individual health. Even modest weight changes (5–10% of body weight) can improve blood pressure, blood sugar, and cholesterol. Your GP can discuss diet, activity, and whether treatment options may be suitable for you.
Do different ethnic groups have different BMI thresholds?
Yes. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, or Black Caribbean heritage because these groups face higher cardiovascular and diabetes risk at lower BMI levels. Discuss your personal thresholds 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.