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
Check My Body Mass Index — What Your Results Mean
Body mass index (BMI) is a quick screening tool that helps you understand whether your weight falls within a healthy range for your height. Using our free BMI calculator above, you can check your personal BMI instantly by entering your height and weight in either metric (kg and cm) or imperial (stone and pounds) measurements. Your BMI score is one useful metric, though it's important to understand both what it tells you and its limitations when assessing overall health and body composition.
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 Calculator Results
Once you've checked your BMI using the calculator on this page, here's how to interpret your result according to NHS guidelines:
- Below 18.5: Underweight — may warrant discussion with your GP about whether your weight is healthy for you
- 18.5 to 24.9: Healthy weight — falls within the NHS recommended range for most adults
- 25.0 to 29.9: Overweight — above the healthy range but not yet classified as obese
- 30.0 to 34.9: Obese (Class I) — significantly above healthy range; increased health risks
- 35.0 to 39.9: Obese (Class II) — further increased health risks
- 40.0 and above: Severely obese (Class III) — highest health risk category
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. The NHS recommends a healthy weight range of 18.5 to 22.9 for these populations, as they face higher cardiovascular and diabetes risk at the same BMI as other adults. Your GP can discuss whether your individual BMI target should be adjusted based on your ethnicity and health profile.
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.
BMI vs Body Composition — When to Use Each Metric
While BMI is a useful and quick screening tool, it has important limitations. BMI does not distinguish between muscle and fat — an athlete with high lean body mass may have a high BMI despite low body fat percentage, while another person at the same BMI might have significantly higher body fat. For a more complete picture of your health, consider body fat percentage alongside your BMI. Body composition analysis, which measures your actual fat, muscle, and bone mass, gives you more detailed information than BMI alone. Visceral fat (fat stored around organs) is particularly important to monitor, as it poses greater health risks than subcutaneous fat under the skin. Use the weight converter on this page to track your progress, and discuss your individual health targets with your GP — they can assess both your BMI and body composition 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 is a healthy BMI for a UK adult?
According to NHS guidance, a healthy BMI for most UK adults is between 18.5 and 24.9. If you're from a South Asian, Chinese, Black African, or Black Caribbean background, the healthy range is 18.5 to 22.9. Check your personal BMI using our free calculator above to see where you fall.
Can I have a high BMI but still be healthy?
Yes, in some cases. Athletes with significant muscle mass may have high BMI but low body fat percentage. BMI doesn't measure body composition directly. However, for most people, a BMI over 30 indicates increased health risks. Your GP can assess your overall health considering multiple factors beyond BMI alone.
Does BMI apply to children?
No. Children's BMI is calculated differently using age and sex-specific growth charts (UK90 centiles), not adult categories. If you're concerned about your child's weight, consult your GP or health visitor, who can assess using appropriate child growth references.
What's the difference between BMI and body fat percentage?
BMI measures weight relative to height but doesn't distinguish muscle from fat. Body fat percentage measures actual fat mass and gives a more complete picture of body composition. Both are useful — BMI is quick and accessible, while body fat percentage is more precise for understanding actual body composition.
Should I aim for the lowest possible BMI?
No. BMI below 18.5 (underweight) can indicate health risks including nutrient deficiency and weakened immunity. The goal is reaching a BMI within your healthy range (18.5–24.9 for most adults), not the lowest possible figure. Your GP can help you set an appropriate target weight.
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.