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 A BMI And Why Does It Matter?
BMI stands for Body Mass Index — a simple calculation that estimates whether your weight is healthy for your height. It's used by the NHS and healthcare professionals across the UK to screen for weight-related health risks. BMI isn't perfect, but it's a practical starting point for understanding your weight health. Use our free BMI calculator above to check your personal BMI instantly, and discover which NHS category your weight falls into.
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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.
How BMI Is Calculated And NHS Categories
BMI formula: Weight (kg) ÷ height (m)². For example, someone weighing 70kg who is 1.75m tall would have a BMI of approximately 22.9, which falls in the healthy weight range.
The NHS BMI range divides adults into categories:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight (this is the target for most UK adults)
- 25.0–29.9: Overweight
- 30.0–34.9: Obese (Class I)
- 35.0–39.9: Obese (Class II)
- 40.0+: Severely obese (Class III)
These healthy BMI thresholds are the NHS standard for most UK adults of European heritage. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply — your healthy weight range starts at BMI 18.5–22.9 instead. This is because these populations face higher health risks at lower BMI levels.
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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.
Understanding BMI Limitations And Complementary Measures
BMI has important limitations. It doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also ignores where fat is stored; belly fat poses greater health risks than fat stored elsewhere, which is why waist circumference matters too. The NHS recommends measuring your waist: over 94cm (37in) for men or 80cm (31.5in) for women indicates increased health risk.
For a complete picture of your weight health, use our free weight converter to check your weight in different units, and combine BMI with waist measurement, fitness level, and overall health markers. Your GP can provide personalised guidance about what your BMI means for your individual health.
- 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.
Is BMI the same for men and women?
The BMI formula is identical for both men and women — weight divided by height squared. However, body composition differs between sexes. Women typically have naturally higher body fat percentages than men at the same BMI, so some experts suggest slightly adjusted ranges for women, though the NHS uses the same official categories for all adults.
Why does ethnicity affect BMI categories?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations develop type 2 diabetes and heart disease at lower BMI levels than European populations. The NHS therefore recommends lower thresholds for these groups — healthy BMI starts at 18.5–22.9 rather than 18.5–24.9. Always discuss your ethnicity-specific health risks with your GP.
What is a good BMI for my height?
A healthy BMI falls between 18.5 and 24.9 for most UK adults (or 18.5–22.9 if you're of South Asian, Chinese, Black African, or Black Caribbean heritage). To find your personal healthy weight range at your height, use the free BMI calculator on this page — it will show you the kg and stone range for your height.
Can I have a high BMI and still be healthy?
Possibly, if you have significant muscle mass (athletes, for example). However, BMI is a screening tool — if your BMI is above 25, it's worth discussing with your GP, especially if combined with other risk factors like large waist circumference, high blood pressure, or family history of diabetes. Your GP can assess your overall health.
How often should I check my BMI?
Checking your BMI every 3–6 months is reasonable if you're monitoring weight changes. Don't obsess over small fluctuations — weight naturally varies by 1–2kg day-to-day due to hydration and food intake. Track longer-term trends instead. Use our free progress tracker to log changes over weeks and months for a clearer picture.
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.