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 is an NHS BMI Test?
An NHS BMI test is a simple health screening tool your GP can use to assess whether your weight is healthy for your height. BMI stands for Body Mass Index, and it's calculated using your weight in kilograms divided by your height in metres squared. The NHS uses standardised BMI categories to help identify whether you're at a healthy weight or at increased health risk. While BMI is a useful starting point, your GP will also consider other factors like waist measurement and overall health when assessing your weight. Use our free BMI calculator above to check 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 Healthy Ranges
The NHS BMI formula is straightforward: weight (kg) ÷ height (m)². The NHS uses four main BMI categories to classify adults' weight status:
- 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
Importantly, the NHS recognises that people of South Asian, Chinese, Black African, and Black Caribbean heritage face higher health risks at lower BMI levels, so lower BMI thresholds apply: a healthy range is 18.5 to 22.9, overweight begins at 23.0, and obese begins at 27.5. This reflects evidence showing these groups have greater cardiovascular and metabolic risk at the same BMI as white European populations. Your GP can calculate your personal BMI range and discuss what it means for your individual health.
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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.
Important Limitations of BMI Testing
While BMI is a useful screening tool, it has significant limitations. BMI cannot distinguish between muscle and fat — athletes and people with high muscle mass may have a high BMI but low body fat percentage. BMI also ignores where fat is stored; excess fat around the stomach (visceral fat) poses greater health risk than fat elsewhere, which is why your GP may measure your waist circumference too. BMI is less accurate for older adults who naturally lose muscle with age, during pregnancy, or for very tall or very short individuals. For a complete health picture, your GP may combine your BMI result with blood pressure, cholesterol levels, blood sugar, and lifestyle factors before making any health recommendations.
- 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.
Can I calculate my BMI using the BMI formula at home?
Yes, absolutely. Use the simple formula: weight in kg ÷ (height in m)². For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4, which falls in the healthy range. Our free BMI calculator above does this instantly for you.
What's the difference between overweight and obese according to the NHS?
According to NHS BMI categories, overweight is a BMI of 25.0 to 29.9, while obese begins at 30.0. However, BMI is just one health indicator — your GP will assess your overall health, not just your BMI number, before discussing any health concerns or treatment options.
Why does the NHS have different BMI thresholds for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage develop type 2 diabetes and heart disease at lower BMI levels than white European populations. The NHS recommends lower thresholds (healthy BMI 18.5–22.9, overweight from 23.0) for these groups to reflect this evidence-based risk.
Should I worry if my BMI is high but I feel healthy?
BMI is just one screening tool. If your BMI is elevated, your GP will assess other factors including waist circumference, blood pressure, blood sugar, fitness level, and family history. Even a modest weight loss of 5–10% can improve health markers. Speak to your GP about your individual situation.
Does NHS BMI testing include waist measurement?
While BMI is the primary calculation, many GPs also measure waist circumference as it's a better indicator of visceral fat and cardiovascular risk. A waist over 94cm (37in) for men or 80cm (31.5in) for women suggests increased health risk. Your weight converter tool can help track changes across different units.
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.