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
Understanding Body Mass Index (BMI) — NHS Guidelines
Body mass index (BMI) is a measurement used by the NHS to screen for weight-related health risks in adults. It's calculated using your height and weight, and helps your GP determine whether you're in a healthy weight range. While BMI isn't perfect—it doesn't account for muscle mass or fat distribution—it remains the NHS's primary tool for assessing population health. Understanding your BMI is an important first step in managing your weight and health. Use our free BMI calculator above to find your personal BMI instantly, then read on to understand what your result means according to NHS guidelines.
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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 Healthy Weight Ranges
The NHS uses a standardised BMI formula to classify adults into health categories. Your BMI range UK is calculated as: weight (kg) ÷ height (m)².
- Healthy BMI: 18.5 to 24.9 — associated with lowest health risks
- Overweight BMI threshold: 25.0 to 29.9 — increased risk of type 2 diabetes and cardiovascular disease
- Obese (Class I): 30.0 to 34.9 — significantly increased health risks
- Obese (Class II): 35.0 to 39.9 — very high health risks
- Severely obese: 40.0 and above — severe health risks requiring medical support
For adults of South Asian, Chinese, Black African, and Black Caribbean heritage, the NHS recommends lower thresholds. These groups face higher cardiovascular and diabetes risk at lower BMI levels, so a healthy BMI for these populations starts at 18.5 and goes up to 22.9. This reflects important ethnic variations in health risk that standard BMI categories UK don't capture. Your GP can advise on which thresholds apply to you personally.
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 Support and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers a structured weight management pathway. Tier 1 involves self-help tools and community programmes. Tier 2 includes primary care interventions like the NHS Weight Loss Plan, available free online. Tier 3 is specialist multidisciplinary weight management services, where prescription medications like GLP-1 injections may be considered for eligible adults. Tier 4 involves bariatric surgery for severe obesity.
You don't need to wait until your BMI reaches a certain point to seek support—speak to your GP if you're concerned about your weight or health. Even modest weight loss of 5–10% can improve blood pressure, blood sugar control, and reduce your risk of serious disease. Our weight converter helps you track changes in familiar UK units (stone and pounds), while our free progress tracker lets you log your weight loss journey 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.
What is a healthy BMI according to NHS guidelines?
The NHS defines a healthy BMI as between 18.5 and 24.9 for most adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower upper threshold of 22.9 due to increased health risks at higher BMI levels. Your GP can advise on what's healthy for you personally.
What are the BMI limitations I should know about?
BMI limitations are significant—it doesn't distinguish between muscle and fat, so athletes may have high BMI but low body fat. BMI also doesn't account for where fat is stored (belly fat is riskier) or apply accurately to elderly people, pregnant women, or very muscular individuals. Use BMI as a screening tool alongside waist measurement and GP advice.
How do I access NHS weight management support?
Start by speaking to your GP, who can refer you to tier 2 community programmes or tier 3 specialist services depending on your BMI and health needs. The NHS Weight Loss Plan is free and available online. Availability varies by region, and waiting times for specialist services can be long, so speak to your GP early if you need support.
What does overweight BMI threshold mean for my health?
An overweight BMI (25.0 to 29.9) indicates increased risk of type 2 diabetes, heart disease, and high blood pressure compared to the healthy range. However, risk isn't automatic—many people with overweight BMI are metabolically healthy. Your GP can assess your individual risk based on your whole health picture, not just BMI.
Can I calculate my healthy weight range from my height?
Yes. For any height, the healthy BMI range converts to a weight range. For example, at 5ft 8in (173cm), healthy weight is roughly 55–74kg (8st 10lbs–11st 9lbs). Use our free BMI calculator and weight converter above to find your personal healthy range, then discuss targets with your GP.
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.