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
What Is a BMI Machine and How Does It Work?
A BMI machine is a health screening device that calculates your Body Mass Index — a measurement of body weight relative to height. These machines, often found in GP surgeries, gyms, and pharmacies across the UK, use your weight and height to generate a BMI result instantly. However, it's important to understand what a BMI machine actually measures and its limitations. Our free BMI calculator above provides the same calculation using the standard BMI formula, giving you accurate results whenever you need them.
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 BMI Machines Calculate Your BMI Range
BMI machines use a simple mathematical formula to determine your BMI category. The BMI formula divides your weight in kilograms by your height in metres squared (BMI = weight ÷ height²). Once calculated, your result is compared against NHS BMI categories to determine whether you fall into underweight, healthy weight, overweight, or obese ranges.
The standard BMI range UK categories are:
- Below 18.5 = Underweight
- 18.5 to 24.9 = Healthy weight
- 25.0 to 29.9 = Overweight
- 30.0 and above = Obese
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy BMI threshold is lower — the NHS recommends a BMI range UK starting at 18.5 to 22.9 for healthy weight, as these groups face higher health risks at lower BMI levels. Most BMI machines display your result instantly, making them a quick screening tool in clinical and community settings.
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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.
Important BMI Machine Limitations and Complementary Measures
While BMI machines offer a quick calculation, they have significant limitations. BMI limitations include the fact that BMI does not distinguish between muscle and fat — athletes or people with high muscle mass may have a high BMI but low body fat percentage. Additionally, BMI does not account for where fat is stored on your body, which is important for health risk assessment.
The NHS recommends using BMI alongside other health measures, particularly waist circumference. For men, a waist measurement over 102cm (40in) indicates high health risk; for women, over 88cm (34.5in) is high risk. For a complete picture of your health, speak with your GP who can assess your individual circumstances and may recommend additional measurements like body composition analysis or blood pressure checks.
- 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 accurate are BMI machines?
BMI machines are accurate at calculating the BMI formula itself, using the standard weight-to-height ratio. However, the accuracy of your BMI result depends on the machine being calibrated correctly and you inputting your correct height and weight. The real limitation is not the machine's accuracy, but that BMI itself has limitations — it doesn't distinguish muscle from fat.
What's the difference between a BMI machine and a BMI calculator?
A BMI machine is a physical device, usually found in gyms or medical settings, that measures your weight and height in one step. A BMI calculator (like the free tool on this page) requires you to input your own measurements. Both use the identical BMI formula, so results are the same — it's just a matter of convenience and setting.
Can a BMI machine tell me if I'm overweight?
Yes, a BMI machine will calculate your BMI and place you into a category — underweight, healthy weight, overweight, or obese. However, a BMI machine alone cannot tell you about your overall health. Your GP can interpret your BMI result in context with your age, medical history, waist measurement, and other factors to give you personalised health advice.
Are BMI machines available on the NHS in the UK?
Many NHS GP surgeries have scales and height measures available, and staff can calculate your BMI during appointments. Some NHS community health services and weight management clinics also have BMI machines. However, not all surgeries have dedicated machines — you can always ask your GP to measure and calculate your BMI, or use our free BMI calculator online.
Do I need a BMI machine to check my BMI?
No. You only need to know your weight (in kg) and height (in metres). You can use our free BMI calculator on this page, a simple online calculator, or ask your GP. The advantage of a physical BMI machine is convenience in one location, but the calculation is identical whether done by machine or calculator.
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.