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
How To Calculate BMI Of Your Body
Body Mass Index (BMI) is a straightforward measurement that uses your weight and height to assess whether you're in a healthy range. Calculating your BMI takes just two measurements and a simple formula—and it's one of the most useful health screening tools available. In the UK, the NHS uses BMI categories to help identify whether someone's weight poses a health risk. Whether you want to understand your own BMI or track changes over time, knowing how to calculate it is the first step. Our free BMI calculator above does this instantly, but understanding the maths behind it helps you make sense of the result.
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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.
The BMI Formula And How To Use It
The BMI formula is simple: divide your weight in kilograms by your height in metres squared. Mathematically: BMI = weight (kg) ÷ height (m)². Here's a practical example: if you weigh 70kg and are 1.75 metres tall, you'd calculate: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. This gives you a BMI of 22.9, which falls in the healthy weight range according to NHS guidelines. The NHS BMI categories are: Underweight (below 18.5), Healthy weight (18.5–24.9), Overweight (25.0–29.9), Obese Class I (30.0–34.9), Obese Class II (35.0–39.9), and Severely obese (40.0+). If you prefer working in stone and pounds, you can still use the formula—simply convert your measurements to metric first using a weight converter, or use our free BMI calculator above which handles all the conversions automatically.
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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 is a useful screening tool, it has important BMI limitations. BMI doesn't distinguish between muscle and fat—so athletes or very muscular people may have a high BMI despite low body fat. It also doesn't account for where fat is stored on your body; abdominal fat poses greater health risks than fat stored elsewhere. For a more complete picture, the NHS recommends also checking your waist circumference: over 94cm for men or 80cm for women indicates increased health risk. Age, ethnicity, and bone density also affect what a healthy BMI means for you personally. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds—healthy weight starts at 18.5 but overweight begins at 23.0 rather than 25.0. Your GP can give you personalised advice about what your individual BMI means for your 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 the BMI formula different for men and women?
No—the BMI formula is identical for men and women: weight (kg) ÷ height (m)². However, healthy BMI ranges and body fat percentages do differ between genders due to biological differences. The same BMI category applies to both, but women typically carry more body fat at the same BMI than men.
Can I calculate BMI using stone and pounds?
Yes, but it's easier to convert to metric first. If you weigh 11 stone (154.2kg) and are 5ft 8in (1.73m), convert to kg, then use the formula. Alternatively, use our free weight converter to switch between stone and kilograms instantly.
What if my BMI is higher—should I be worried?
A higher BMI may indicate increased health risk, but BMI is just one screening tool. Other factors matter: waist circumference, fitness level, diet, family history, and overall health. Speak to your GP for personalised advice about what your BMI means and whether action is needed.
Why does ethnicity affect BMI thresholds?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean descent face higher risks of type 2 diabetes and heart disease at lower BMI levels than white Europeans. The NHS reflects this by recommending lower healthy BMI ranges (18.5–22.9 instead of 18.5–24.9) for these groups.
How often should I calculate my BMI?
Calculating BMI monthly or quarterly is useful for tracking progress if you're working on weight changes. However, weight fluctuates daily due to hydration, hormones, and digestion—focus on longer-term trends rather than single measurements. Our free progress tracker can help you log and monitor changes over time.
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.