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 Are BMI Categories and Why Do They Matter?
BMI categories are standardised ranges that help you understand whether your weight is healthy for your height. According to NHS guidelines, your BMI falls into one of five main categories: underweight, healthy weight, overweight, obese, or severely obese. These categories are based on the BMI formula and help identify health risks associated with excess weight. Understanding where your BMI sits is a useful first step in assessing your overall health, though it's important to remember that BMI is a screening tool, not a diagnosis. You can calculate your personal BMI instantly using our free BMI calculator above to see which category you fall into.
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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 Their Health Significance
The BMI formula is simple: weight (kg) divided by height in metres squared. According to NHS BMI guidelines, here are the standard categories for UK adults:
- Underweight: BMI below 18.5 — may indicate nutritional concerns
- Healthy weight: BMI 18.5 to 24.9 — associated with lowest health risks
- Overweight: BMI 25.0 to 29.9 — increased risk of weight-related health conditions
- Obese (Class I): BMI 30.0 to 34.9 — significantly increased health risks
- Obese (Class II): BMI 35.0 to 39.9 — very high health risks
- Severely obese (Class III): BMI 40.0 or above — highest health risks
For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the overweight BMI threshold starts at 23.0 (not 25.0) and obese classification begins at 27.5, because these groups have higher cardiovascular and diabetes risk at lower BMI levels. Use our free BMI calculator above to find your exact category in seconds.
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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.
BMI Limitations and What Else You Should Consider
While BMI limitations exist, it remains a useful screening tool. BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat percentage. It also doesn't account for where fat is stored (belly fat carries higher health risk) or age-related muscle loss in older adults. The NHS recommends considering waist circumference alongside BMI: men over 94cm and women over 80cm have increased health risk, whilst measurements over 102cm (men) or 88cm (women) indicate high risk. Your GP can provide personalised health advice beyond BMI. Our free weight converter helps you check your weight across different units, making it easier to monitor your progress 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 range?
According to NHS guidelines, a healthy BMI range for UK adults is 18.5 to 24.9. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9. Use our free BMI calculator to check your personal BMI instantly.
Why are BMI categories different for some ethnic groups?
Research shows that people from South Asian, Chinese, Black African, and Black Caribbean backgrounds have a higher risk of type 2 diabetes and heart disease at lower BMI levels. The NHS therefore recommends lower thresholds for these groups to enable earlier identification of health risks.
Is BMI accurate for muscular people?
No. BMI cannot distinguish between muscle and fat, so very muscular individuals may have a high BMI despite low body fat. This is one key limitation of BMI. Your GP can assess your overall health using additional measurements like waist circumference.
What health risks come with being in the obese BMI range?
Being in the obese BMI range (30 or above) significantly increases risk of type 2 diabetes, high blood pressure, heart disease, certain cancers, osteoarthritis, and sleep apnoea. Even losing 5 to 10% of your body weight can meaningfully improve these risks.
How do I use the BMI formula to calculate my own BMI?
The BMI formula is: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 22.9 BMI. However, our free BMI calculator above does this instantly — just enter your weight and height.
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.