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
Body Mass Index Calculator — Understanding Your Results
A body mass index calculator instantly calculates your BMI using your height and weight. BMI is a simple screening tool that helps assess whether you're at a healthy weight range according to NHS guidelines. Enter your measurements above to get your result, then use the reference ranges below to understand what your BMI means. Remember that BMI is just one part of the health picture — other factors like body composition, fitness level, and where fat is stored also matter.
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
Your BMI result falls into one of several NHS categories. A healthy BMI is between 18.5 and 24.9 for most UK adults. If your result is between 25.0 and 29.9, you're classed as overweight. A BMI of 30.0 or above falls into the obese category, which increases health risks. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: a healthy BMI for these groups is 18.5 to 22.9, and overweight starts at 23.0.
Important limitations: BMI does not distinguish between muscle and fat. Athletes or very muscular individuals may have a high BMI but low body fat percentage. Conversely, sedentary individuals may have a "normal" BMI but poor body composition with excess visceral fat. Your GP can provide personalised guidance based on your individual 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.
Body Mass Index vs Body Composition — Which Matters More?
BMI is a useful starting point for screening, but body composition analysis provides a more complete picture. While BMI uses only height and weight, body fat percentage measures the proportion of fat versus lean muscle. Two people with identical BMI can have very different health profiles depending on their fitness level and body fat distribution.
Our free BMI calculator on this page gives you an gradual improvement, and you can also use our body fat calculator to estimate your body composition. For the most accurate body composition assessment, your GP or a health professional can arrange more detailed measurements like DEXA scanning. Neither tool replaces clinical judgment — use them alongside professional health advice.
- 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 normal BMI range in the UK?
According to NHS guidelines, a healthy BMI for most UK adults is 18.5 to 24.9. A BMI between 25.0 and 29.9 is classed as overweight, and 30.0 or above is obese. For adults of South Asian, Chinese, Black African, or Black Caribbean descent, the healthy range is lower: 18.5 to 22.9.
Is a high BMI always unhealthy?
Not always. BMI does not account for muscle mass, so athletes or very muscular people may have a high BMI but low body fat and good health. However, for the general population, a BMI above 25 increases health risks. Your GP can assess your individual situation more thoroughly.
Can BMI be inaccurate?
Yes. BMI doesn't distinguish between fat and muscle, doesn't measure visceral fat (dangerous belly fat), and doesn't account for age or body frame size. It's a screening tool only. Body composition analysis using lean body mass measurements provides more detail but requires specialist equipment.
What should I do if my BMI is high?
If your BMI is above the healthy range, discuss it with your GP. Small changes like increasing physical activity, adjusting diet, or seeking support from NHS weight management services can help. NHS tier 3 specialist services offer evidence-based programmes tailored to your health needs.
How is BMI different from body fat percentage?
BMI uses height and weight only. Body fat percentage measures the actual proportion of fat tissue versus lean mass. Someone with normal BMI might have high body fat (poor composition), while someone with higher BMI might be muscular with low body fat. Both metrics together give a fuller health picture.
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.