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 Must Score Calculator — NHS Health Guidance
Your BMI (Body Mass Index) is a key health screening tool used by the NHS to assess whether your weight is healthy for your height. Understanding your BMI helps you know where you fall in the official NHS BMI categories and whether lifestyle changes or GP support might help. Our free BMI calculator above gives you your instant score, plus clear NHS-aligned guidance on what it means. BMI isn't perfect — it doesn't account for muscle or where fat is stored — but it's the starting point the NHS uses for weight health conversations.
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 Your Score Means
The NHS uses five BMI categories to assess weight health in UK adults. These thresholds are based on evidence linking BMI to health risks:
- Below 18.5: Underweight — associated with potential nutritional deficiency risks
- 18.5 to 24.9: Healthy weight — the target range the NHS recommends
- 25.0 to 29.9: Overweight — increased risk of type 2 diabetes and heart disease
- 30.0 to 34.9: Obese (Class I) — significantly elevated health risks
- 35.0 to 39.9: Obese (Class II) — high health risks requiring GP discussion
- 40.0 and above: Severely obese (Class III) — very high risk; NHS specialist support recommended
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher cardiovascular and diabetes risk at the same BMI. A healthy BMI for these groups starts at 18.5 but extends only to 22.9, with overweight beginning at 23.0.
Clinically BackedWeight Loss
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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 to support you. Start with Tier 1: self-help tools, digital programmes, and community support. Your GP can refer you to Tier 2: behaviour change programmes and local weight management services. For BMI over 30 with health conditions, or BMI over 35, you may qualify for Tier 3: specialist multidisciplinary weight management services, where prescription weight loss medications may be considered. Use our free BMI calculator above to find your score, then discuss next steps with your GP. They can assess your individual health and recommend the most appropriate support for you.
- 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 the BMI formula and how is it calculated?
BMI is calculated as weight (kg) divided by height in metres squared. For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73)² = 23.4 — a healthy weight. Our BMI calculator handles this instantly using the NHS formula.
Why do South Asian and Black African adults have different BMI thresholds?
The NHS recommends lower thresholds (healthy weight up to 22.9, not 24.9) because research shows these groups develop type 2 diabetes and heart disease at lower BMI levels. This reflects genetic and metabolic differences that increase health risk at the same BMI as other populations.
What are the limitations of BMI as a health measure?
BMI doesn't distinguish muscle from fat — athletes may have high BMI but low body fat. It also ignores where fat is stored (belly fat carries higher health risk). BMI is less accurate for elderly people, pregnant women, and children. Your GP can assess other health markers alongside BMI.
When should I see my GP about my BMI?
If your BMI is below 18.5 or above 25, discuss it with your GP. They'll assess your individual health, family history, and any weight-related conditions. Even within the healthy range, your GP can offer lifestyle advice. For BMI above 30, GP referral to specialist weight management services may be appropriate.
What does the NHS recommend for healthy, sustainable weight loss?
The NHS recommends losing 0.5 to 1 kg per week through a reduced-calorie diet and increased physical activity. Aim for a 500-calorie daily deficit. Our free GLP-1 weight loss calculator and progress tracker can help you plan and monitor your journey safely.
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.