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 for Adults — What NHS Guidance Says
Body Mass Index (BMI) is the standard measurement used by the NHS to assess whether adults are at a healthy weight. BMI is calculated using your height and weight, and it helps identify if you're at increased risk of weight-related health conditions. However, BMI is a screening tool — it has limitations and doesn't measure body fat directly. Understanding your BMI and what it means for your health is an important first step in health planning.
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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 uses standardised BMI categories to classify adult weight status. These categories are based on large-scale health research and apply to most UK adults aged 18 and over.
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obese (Class I): BMI 30.0 to 34.9
- Obese (Class II): BMI 35.0 to 39.9
- Severely obese (Class III): BMI 40.0 and above
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at lower weights. For these populations, healthy weight ranges from 18.5 to 22.9, and overweight begins at 23.0. Calculate your personal BMI using our free BMI calculator above to find your exact category.
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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
The NHS offers a structured weight management pathway to help adults at any BMI level. If your BMI is 25 or above, or if you have weight-related health concerns, your GP can provide guidance and support. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results. Your GP can refer you to specialist weight management services (Tier 3) if needed, where you may be offered structured programmes, dietary advice, or prescription weight loss treatments alongside lifestyle changes. Early action is important — even a 5% reduction in body weight can bring meaningful health benefits.
- 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 does BMI stand for and how is it calculated?
BMI stands for Body Mass Index. The BMI formula is your weight in kilograms divided by your height in metres squared. For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. Our BMI calculator computes this instantly — just enter your weight and height in either metric or imperial units.
Is BMI accurate for everyone?
BMI is a useful screening tool but has important limitations. It doesn't distinguish between muscle and fat, so athletes may have high BMI despite low body fat. BMI also doesn't account for where fat is stored, bone density, or age-related muscle loss. Your GP can assess your individual situation using BMI alongside other measures like waist circumference and fitness level.
What's the difference between overweight and obese?
Overweight (BMI 25–29.9) and obese (BMI 30 and above) are NHS clinical categories reflecting different levels of health risk. Overweight increases some health risks; obesity significantly increases risks of type 2 diabetes, heart disease, and certain cancers. However, individual health depends on many factors beyond BMI, and your GP can give personalised advice about your specific health.
Should I try to lose weight if my BMI is in the healthy range?
If your BMI is between 18.5 and 24.9, the NHS considers you at a healthy weight. However, health is about more than BMI — fitness, diet quality, mental wellbeing, and waist circumference all matter. Your GP can advise whether any lifestyle changes would benefit your personal health. Use our weight converter and BMI calculator to track changes over time if you choose to make adjustments.
Can I use BMI if I'm pregnant, elderly, or very muscular?
BMI has limitations for these groups. During pregnancy, standard BMI categories don't apply — your GP will use different guidance. In older adults, lower BMI may actually reflect age-related muscle loss rather than health. Very muscular individuals (athletes, bodybuilders) often have high BMI despite low body fat. Always discuss your personal situation with your GP for tailored advice about your health.
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.