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 Ideal BMI Index?
An ideal body mass index (BMI) for most UK adults falls between 18.5 and 24.9 according to NHS guidelines. Your BMI is a simple measurement based on your height and weight that helps indicate whether you're at a healthy weight range. However, it's just one health indicator — it doesn't account for muscle mass, bone density, or where fat is stored on your body. Use our free BMI calculator above to find your personal BMI instantly and see where you fall within the healthy range.
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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 Ranges
The NHS uses a standardised body mass index classification system to assess weight categories across UK adults. Your bmi formula is calculated by dividing your weight in kilograms by your height in metres squared (kg ÷ m²). Here are the official BMI categories UK guidelines:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9 — the ideal range
- 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: BMI 40.0 and above
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — a healthy BMI starts at 18.5 but moves to 22.9 as the upper limit, reflecting higher cardiovascular risk at standard BMI levels. Use our weight converter to check your current weight in kg, then calculate your exact BMI range UK using the calculator on this page.
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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 What Else Matters
While BMI limitations are important to understand, your BMI provides a useful screening tool for health risk assessment. The key limitation: BMI cannot distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. Additionally, BMI doesn't account for age, bone density, or where fat is stored — excess abdominal fat carries higher health risks than fat stored elsewhere. The NHS recommends also measuring your waist circumference: over 94cm (37 inches) for men and 80cm (31.5 inches) for women indicates increased health risk. Your GP can provide personalised guidance on what your ideal weight should be based on your overall health profile, not BMI alone.
- 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 considered an ideal BMI for UK adults?
The NHS defines an ideal BMI as between 18.5 and 24.9 for most UK adults. For South Asian, Chinese, and Black African/Caribbean adults, the upper healthy limit is 22.9. Everyone's ideal weight varies based on muscle mass, bone structure, and overall health — your GP can advise what's right for you personally.
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared (kg ÷ m²). For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = BMI of 22.9. Use our free BMI calculator above for gradual improvement across both metric and imperial measurements.
Is a BMI of 25 considered overweight?
Yes, according to NHS guidelines, a BMI of 25.0 to 29.9 falls in the overweight category. However, this is just one indicator. Factors like muscle mass, waist circumference, and overall fitness also matter for your health. Your GP can assess whether your weight poses any health risks.
Why do South Asian adults have different BMI thresholds?
Research shows that South Asian, Chinese, Black African, and Black Caribbean adults develop weight-related health conditions at lower BMI levels than other populations. The NHS therefore recommends lower thresholds for these groups to ensure earlier identification of increased health risk.
What if my BMI is in the healthy range but I still feel overweight?
BMI doesn't measure body composition — you could have a healthy BMI but high body fat, or an elevated BMI but high muscle mass. Waist circumference, how you feel, and your energy levels matter too. Your GP or a registered dietitian can provide personalised advice beyond BMI alone.
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.