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
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Body Mass Index Converter — Understanding Your BMI Results
A body mass index converter helps you calculate your BMI from your weight and height, translating that number into meaningful health context. Whether you're tracking your health or understanding what your measurements mean, knowing how to interpret BMI results is essential. The BMI calculator on this page instantly converts your weight (in kg, stone, or lbs) and height to show where you fall on the NHS BMI scale. Use our free BMI calculator above to find your personal BMI and discover what it means for your health.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 to Interpret Your BMI Results by Gender
BMI results are interpreted the same way for both men and women, using NHS-approved categories. However, body fat percentage and body composition can differ between genders at the same BMI — women typically carry more essential fat than men.
- BMI 18.5–24.9: Healthy weight range (aim here for best health outcomes)
- BMI 25.0–29.9: Overweight (increased health risk)
- BMI 30.0–34.9: Obese Class I (significant health risk)
- BMI 35.0–39.9: Obese Class II (high health risk)
- BMI 40.0+: Severely obese Class III (very high health risk)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — healthy weight is BMI 18.5–22.9, and overweight starts at BMI 23.0.
Remember: BMI does not distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low lean body mass.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
How BMI Compares to Body Fat Percentage and Body Composition
While BMI is a useful screening tool, it has important limits. Body fat percentage and overall body composition provide more detail about your actual health risk. A person with high BMI but significant muscle mass may be healthier than someone with a "normal" BMI but high visceral fat (dangerous fat around organs).
When BMI is most useful: Population-level health screening, initial health assessment, easy self-monitoring. When body composition matters more: Understanding true cardiovascular risk, tracking fitness progress, assessing metabolic health. Many GPs now recommend measuring waist circumference alongside BMI — men over 94cm and women over 80cm face increased health risk even at lower BMI levels.
Use our free weight converter to check your weight in different units, then use the BMI calculator on this page to see your personal result in context.
- 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 the difference between BMI and body fat percentage?
BMI uses weight and height only; it cannot tell muscle from fat. Body fat percentage measures actual fat tissue. A muscular person might have high BMI but healthy body fat percentage. For most people, BMI is a useful starting point, but body composition gives a more complete picture of health.
Is the BMI calculator on this page accurate for athletes?
No — athletes with significant muscle mass will have high BMI but low actual body fat. If you're athletic or very muscular, ask your GP about additional assessments like waist circumference or DEXA scans for a more accurate health picture.
Does BMI mean the same thing for men and women?
Yes — BMI categories are the same. However, women naturally carry more essential fat than men (14–20% vs 6–13%), so a woman might feel healthier at a slightly higher body fat percentage. The BMI calculator shows the same ranges for all genders.
What's a healthy BMI for someone over 65?
Research suggests that adults aged 65+ may have slightly better health outcomes with a BMI of 25–27 rather than strictly under 25. However, this varies by individual health, fitness, and muscle mass. Your GP can advise what's best for you personally.
Can I use this BMI converter if I'm pregnant?
No — BMI calculations don't apply during pregnancy because weight gain is expected and healthy. Use your pre-pregnancy BMI as reference, and follow your midwife's guidance on healthy weight gain for your pregnancy.
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.