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
BMI Using Kilograms and Centimetres
BMI (body mass index) calculated from kilograms and centimetres is the standard measurement used by the NHS to assess whether an adult is at a healthy weight. The formula is straightforward: weight in kg divided by height in metres squared. This simple calculation gives a single number that helps you understand your weight category according to NHS guidelines, though it's important to remember that BMI has limitations and doesn't account for muscle mass or where fat is stored on your body. Use our free BMI calculator above to find your personal BMI instantly using metric measurements.
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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 Thresholds
The NHS uses standard BMI categories to classify weight ranges for UK adults:
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25.0–29.9
- Obese (Class I): BMI 30.0–34.9
- Obese (Class II): BMI 35.0–39.9
- Severely obese (Class III): BMI 40.0 and above
However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these groups face higher health risks at lower BMI levels. For these populations, healthy weight is BMI 18.5–22.9, and overweight starts at BMI 23.0. Your GP can discuss which thresholds are most relevant for your individual circumstances and ethnicity. Remember that BMI limitations include the inability to distinguish between muscle and fat — athletes may have a high BMI but low body fat percentage.
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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.
NHS Weight Management Pathway and When to Seek Help
If your BMI calculation suggests you're overweight or obese, the NHS provides a clear pathway to support. Start by speaking with your GP, who can discuss your weight and any weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Your GP may refer you to a tier 3 specialist weight management service in your area, where you'll receive personalised advice on diet, physical activity, and potentially prescription weight loss support. The NHS recommends gradual weight loss of 0.5–1 kg per week as sustainable and safe. Track your progress using our free progress tracker to monitor changes over time alongside lifestyle improvements.
- 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 is the exact BMI formula using kilograms and centimetres?
The formula is: BMI = weight (kg) ÷ height (m)². To use it, convert your height from centimetres to metres (divide by 100), then square that number. For example, at 170 cm (1.70 m) and 75 kg: BMI = 75 ÷ (1.70)² = 75 ÷ 2.89 = 25.95. Our free BMI calculator handles this instantly.
Is my BMI of 28 considered overweight according to NHS guidelines?
Yes, a BMI of 28 falls in the overweight category (25.0–29.9) according to NHS standards for most UK adults. However, if you're of South Asian or Black African heritage, your threshold is lower — BMI 23.0 and above is considered overweight. Speak with your GP about your specific health context, as BMI is just one measure of health.
Why does the NHS use different BMI thresholds for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean backgrounds develop weight-related health problems like type 2 diabetes and heart disease at lower BMI levels than other populations. The NHS recommends lower thresholds (healthy BMI 18.5–22.9) for these groups to better reflect their individual health risk. Your GP can discuss which guidance applies to you.
What are the main limitations of BMI?
BMI doesn't distinguish between muscle and fat, so muscular athletes may have a high BMI despite low body fat. It also doesn't account for where fat is stored (belly fat poses greater health risks), age-related muscle loss, or bone density. The NHS recommends using BMI alongside waist circumference and other health markers for a fuller picture.
When should I contact my GP about my weight?
Contact your GP if your BMI is consistently above 25, you have weight-related health conditions (diabetes, high blood pressure, sleep apnoea), you're gaining weight despite trying to lose it, or you feel your weight is affecting your health or wellbeing. Your GP can assess your individual situation and refer you to appropriate support services or weight management programmes.
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.