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 Classification — What NHS Guidance Says
BMI classification in the UK follows NHS guidelines that categorise adults into ranges based on their body mass index. Understanding where your BMI falls can help you assess your health risk and know when to speak to your GP. This guide explains the official NHS BMI categories, what they mean for your health, and how to use this information to make informed decisions about your weight. MyWeightCheck's BMI calculator helps you determine your personal BMI instantly.
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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 Health Classifications
The NHS BMI classification system divides adults into five categories based on their body mass index score:
- Underweight: BMI below 18.5 — associated with nutritional risks and potential health concerns
- Healthy weight: BMI 18.5–24.9 — the range where most people have the lowest health risks
- Overweight: BMI 25.0–29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0–34.9 — significantly increased health risks including type 2 diabetes and heart disease
- Obese (Class II): BMI 35.0–39.9 — very high health risks
- Severely obese (Class III): BMI 40.0+ — serious health complications requiring medical management
The healthy BMI range is what the NHS recommends for optimal health. However, BMI alone does not account for muscle mass, bone density, or fat distribution. Use our free weight converter to check your weight in different units, then calculate your BMI with our calculator above.
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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 Guidance and When to Seek Help
NICE guidance and NHS health services recommend that anyone with a BMI above 25 should discuss their weight with their GP, particularly if they have other health conditions like high blood pressure, type 2 diabetes, or sleep apnoea. The NHS offers a structured weight management pathway that includes self-help resources, community programmes, and specialist services depending on your BMI and health needs. If your BMI is 30 or above, you may be eligible for NHS tier 3 specialist weight management services, which can include structured dietary advice, exercise programmes, and in some cases, prescription weight loss medication alongside lifestyle changes. Your GP can refer you to local services and discuss whether additional support is right 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 healthy BMI range according to NHS guidelines?
The NHS defines a healthy BMI for most adults as 18.5 to 24.9. Within this range, health risks from excess weight are lowest. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5 to 22.9 due to increased metabolic risk at higher BMI levels in these populations.
Does a high BMI always mean I'm unhealthy?
BMI is a useful screening tool but has important limitations. It doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. BMI also doesn't account for age, bone density, or where fat is stored. Waist circumference and overall fitness matter too. Your GP can give you personalised health advice beyond just your BMI number.
What should I do if my BMI is over 30?
If your BMI is 30 or above, it's worth speaking to your GP. You may be eligible for NHS weight management support, which could include community programmes, dietary advice, or specialist services. The NHS can help you develop a plan tailored to your health, which may involve gradual lifestyle changes, increased physical activity, and in some cases, additional treatment options.
Are BMI thresholds the same for everyone?
No. The NHS recommends lower BMI thresholds for adults of South Asian, Chinese, Black African, and Black Caribbean backgrounds because these groups face higher risk of type 2 diabetes and heart disease at lower BMI levels. Your GP will consider your ethnicity, age, fitness level, and other health factors when assessing your individual health risk.
How is BMI calculated?
BMI is calculated using the formula: weight (kg) ÷ height (m)². For example, someone weighing 70kg and 1.75m tall has a BMI of about 22.9. You can use our free BMI calculator above to find your BMI instantly, and our weight converter tool to switch between kg, stone, and pounds.
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.