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 NHS Guidance Use It?
A BMI machine is a device that calculates your body mass index — a measurement of body weight relative to height. The NHS uses BMI as a screening tool to help identify whether weight falls into a healthy range. While BMI machines are common in GP surgeries, weight management clinics, and gyms, you don't need one to check your BMI. You can calculate it instantly using our free BMI calculator above, or use the standard BMI formula with your height and weight. This guide explains how NHS professionals interpret BMI results and what the different categories mean for your health.
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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.
NHS BMI Categories and What They Mean
The NHS uses five BMI categories to classify adult weight status. These thresholds are based on health research and help GPs identify whether you're at increased risk of weight-related health conditions.
- Under 18.5: Underweight — may indicate nutritional concerns
- 18.5–24.9: Healthy weight — lowest risk of weight-related diseases
- 25.0–29.9: Overweight — increased risk of type 2 diabetes and heart disease
- 30.0–34.9: Obese (Class I) — significantly increased health risks
- 35.0–39.9: Obese (Class II) — higher health risks
- 40.0 and above: Severely obese (Class III) — very high health risks
NICE guidance also recognises that for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply due to higher disease risk at lower weights. For these groups, healthy weight is 18.5–22.9, and overweight 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.
NHS Weight Management Pathway and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway. Tier 1 begins with self-help tools, digital apps, and community weight loss programmes available free through your GP. Tier 2 involves GP-led behaviour change support. For higher BMI or weight-related health conditions, your GP can refer you to Tier 3 specialist weight management services, where professionals assess your individual needs and may discuss prescription weight loss medication alongside lifestyle support. Track your progress with our free progress tracker as you work toward your health goals.
- 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 if I don't have a BMI machine?
You can calculate BMI using the formula: weight (kg) ÷ height (m)². Our free BMI calculator on this page does this instantly — simply enter your weight and height in metric or imperial units, and you'll see your result aligned with NHS categories.
Is BMI the only measure the NHS uses to assess weight?
No. While BMI is a useful screening tool, the NHS also considers waist circumference, which better indicates belly fat linked to heart disease risk. A healthy waist measurement is under 94cm (37 inches) for men and 80cm (31.5 inches) for women. BMI has limitations too — it doesn't distinguish muscle from fat.
My BMI is in the overweight range. Should I contact my GP?
If your BMI is 25–29.9 and you have no weight-related health conditions, you can start with self-help approaches like the NHS Weight Loss Plan or using our free BMI calculator and progress tracker to monitor changes. If you have diabetes, high blood pressure, or other conditions, contact your GP who can advise on Tier 2 or 3 support.
What's the difference between BMI machines in gyms and NHS assessments?
BMI machines calculate the same way — there's no difference in the maths. However, NHS assessments consider your complete health picture: blood pressure, blood sugar, cholesterol, family history, and symptoms. This is why a GP discussion is more valuable than a machine result alone.
Do BMI machines work accurately for everyone?
BMI calculation is mathematically consistent, but results are less meaningful for athletes (high muscle mass appears as high BMI) and elderly people (muscle loss with age). Use our BMI calculator as a screening tool, but always discuss results with your GP for personalised health context and guidance.
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.