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
BMI Calculator — NHS Guidance for UK Adults
Your body mass index (BMI) is a simple health screening tool that compares your weight to your height. The NHS uses BMI as a key indicator to assess whether you're at a healthy weight and to identify potential health risks. Our free BMI calculator above instantly shows you where you fall on the NHS scale, along with context about what your result means. BMI is quick to calculate but has limitations — it doesn't account for muscle mass or where fat is stored — so your GP may also look at other factors like waist circumference.
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.
NHS BMI Categories and What They Mean
The NHS uses five main BMI categories to assess adult weight:
- Underweight (BMI below 18.5): May indicate malnutrition or underlying health issues — speak to your GP if concerned
- Healthy weight (BMI 18.5–24.9): Associated with the lowest risk of weight-related diseases
- Overweight (BMI 25.0–29.9): Increases risk of type 2 diabetes, high blood pressure, and heart disease
- Obese Class I (BMI 30.0–34.9): Significant health risks — NHS recommends weight management support
- Obese Class II (BMI 35.0–39.9): Higher health risks; NHS often recommends specialist intervention
- Severely obese (BMI 40.0+): Highest risk category; NHS typically offers access to tier 3/4 weight management services
Important: If you are South Asian, Chinese, Black African, or Black Caribbean, the NHS recommends lower BMI thresholds because these groups face higher cardiovascular and diabetes risk at the same BMI. 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 suggests you're overweight or obese, the NHS offers a structured weight management pathway. Tier 1 includes self-help tools and community programmes available to everyone. Tier 2 involves your GP and behaviour change support. Tier 3 is specialist multidisciplinary weight management services, where prescription medications like Mounjaro or Wegovy may be considered alongside diet and exercise. Tier 4 covers bariatric surgery for severe obesity with significant health complications.
Your GP can assess your individual health, discuss weight management options, and refer you to appropriate NHS services. Use our free weight converter to track your weight in stone, kg, or lbs, and our progress tracker to log changes over time.
- 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 using the NHS formula?
BMI = weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.73m tall, your BMI = 70 ÷ (1.73)² = 23.4. Our free BMI calculator above does this instantly — just enter your height and weight in metric or imperial units, and it shows your result alongside NHS categories.
What's the difference between NHS BMI categories and other BMI charts?
The NHS thresholds are UK-specific and based on UK population health data and clinical guidance from NICE. They may differ slightly from other countries' standards. The NHS also recognises that lower thresholds apply to certain ethnic groups due to higher disease risk at the same BMI.
Is BMI the only thing my GP considers for weight health?
No. While BMI is a useful screening tool, GPs also look at waist circumference (especially for men over 94cm and women over 80cm), blood pressure, blood sugar levels, cholesterol, and medical history. BMI doesn't distinguish between muscle and fat, so someone very muscular may have a high BMI despite low body fat.
I'm below the healthy weight range — what does that mean?
A BMI below 18.5 may indicate underweight status, which can be associated with malnutrition, weak immunity, bone loss, or underlying conditions. If you're consistently underweight, speak to your GP — they can investigate causes and advise on nutrition or medical support.
How often should I check my BMI?
The NHS recommends checking your BMI regularly — monthly or quarterly — if you're working on weight management. Use our free progress tracker to log your weight over time and see trends. For general health, annual checks with your GP are standard, but more frequent monitoring may be recommended if you have weight-related health conditions.
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.