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
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BMI Weight Index Chart — What Your BMI Means
Your body mass index (BMI) is a simple measurement that helps you understand whether your weight is healthy for your height. The NHS uses a standardised BMI weight index chart to classify adults into different categories, from underweight through to severely obese. This guide explains what your BMI means, how it's calculated, and what the NHS considers a healthy range for UK adults. Use our free BMI calculator above to work out your personal BMI instantly, then refer to the ranges below to understand your result.
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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 BMI weight index chart divides adults into five categories based on their body mass index:
- Underweight: BMI below 18.5 — may need support to reach a healthy weight
- Healthy weight: BMI 18.5–24.9 — associated with 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
- Obese (Class II): BMI 35.0–39.9 — higher health risks
- Severely obese (Class III): BMI 40.0 and above — very high health risks
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds: healthy weight is BMI 18.5–22.9, and overweight begins at 23.0. This is because these groups face higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. The BMI formula is simple: divide your weight in kilograms by your height in metres squared. Convert your weight between kg, stone, and lbs instantly using the free weight converter on this page.
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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 Matters
While the BMI weight index chart is a useful screening tool, it has important limitations. BMI does not distinguish between muscle and fat — athletes and people with high muscle mass may have a high BMI despite low body fat. BMI also ignores where fat is stored; central belly fat poses greater health risks than fat stored elsewhere. For this reason, the NHS recommends measuring your waist circumference alongside BMI: men should aim for below 94cm (37 inches), women below 80cm (31.5 inches). Age, pregnancy, and certain medical conditions also affect how accurately BMI reflects health. Your GP can provide personalised guidance about what your BMI means for your individual health and whether lifestyle changes or treatment may help.
- 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 the NHS?
The NHS defines a healthy BMI as 18.5–24.9 for most UK adults. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower: 18.5–22.9. These lower thresholds reflect higher cardiovascular and diabetes risk in these populations at standard BMI levels.
How do I calculate my BMI using the formula?
The BMI formula is: weight (kg) ÷ height (metres) squared. For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = BMI 22.9. Use our free BMI calculator above for gradual improvement without doing the maths yourself.
Does a high BMI always mean I'm overweight or unhealthy?
Not necessarily. BMI does not account for muscle mass — athletes and very muscular people may have high BMI but low body fat. BMI also ignores where fat is stored. Waist circumference and overall fitness matter. Always discuss your personal BMI with your GP for context about your health.
What is the difference between overweight and obese on the BMI chart?
According to the NHS, overweight is BMI 25.0–29.9, while obese begins at BMI 30.0. The "obese" category is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+). These distinctions help healthcare professionals assess health risks more precisely.
Should I use different BMI ranges if I'm Asian or Black British?
Yes. The NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults because research shows these groups have higher cardiovascular and diabetes risk at lower BMI levels. For these groups, healthy weight is 18.5–22.9, and overweight begins at 23.0.
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.