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 in Kilograms — How It's Calculated and What It Means
BMI (Body Mass Index) is calculated using your weight in kilograms and your height in metres. It's a simple screening tool used by the NHS to assess whether adults fall into a healthy weight range. Understanding your BMI in kilograms helps you see where you stand health-wise according to UK guidelines. Use our free BMI calculator above to work out your personal BMI instantly, or read on to learn how the formula works and what your result means.
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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 to Calculate BMI Using Kilograms
The BMI formula is straightforward: divide your weight in kilograms by your height in metres, then divide by your height again (or multiply by height squared). For example, if you weigh 70kg and are 1.75m tall, your calculation is 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9 BMI.
Once you have your BMI number, the NHS BMI categories UK tell you what range you fall into:
- Below 18.5: Underweight
- 18.5–24.9: Healthy weight
- 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)
The healthy BMI range for most UK adults is 18.5 to 24.9. However, for adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the NHS recommends lower thresholds — a healthy BMI starts at 18.5 but only goes up to 22.9, and the overweight BMI threshold begins at 23.0.
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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 to Consider
While BMI is a useful screening tool, it has real limitations. BMI limitations include the fact that it doesn't distinguish between muscle and fat — athletes or very fit individuals may have a high BMI but low body fat. BMI also doesn't account for where fat is stored on your body, which matters for health risk. Age, bone density, and ethnicity all affect what a healthy BMI really means for you.
The NHS recommends looking at waist circumference alongside BMI: men should aim for under 94cm, women under 80cm. Your GP can give you personalised health advice and discuss whether your weight poses any health risks. Use our free weight converter to track your weight in different units, and remember that healthy weight loss is gradual — around 0.5–1kg per week.
- 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 BMI in kilograms?
Divide your weight in kilograms by your height in metres squared. For example, 75kg ÷ (1.73m × 1.73m) = 75 ÷ 2.99 = 25.1 BMI. Our free BMI calculator above does this instantly for you.
What is a healthy BMI range according to the NHS?
The NHS healthy BMI range is 18.5 to 24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the range is 18.5 to 22.9 due to higher health risks at higher weights.
What does an overweight BMI mean?
A BMI between 25.0 and 29.9 falls into the overweight category. This suggests your weight may increase certain health risks. Your GP can discuss whether lifestyle changes or further assessment would be helpful for you personally.
Does BMI measure body fat percentage?
No — BMI doesn't distinguish between muscle and fat. Two people with the same BMI can have very different body compositions. Waist measurement and body composition analysis give a fuller picture of your health.
Why do different ethnic groups have different BMI thresholds?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean backgrounds have higher cardiovascular and diabetes risk at lower BMI levels than white Europeans, so the NHS recommends lower thresholds for these groups. ```
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.