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
How to Measure and Calculate Your BMI
Measuring your BMI (Body Mass Index) is a simple way to assess whether your weight is in a healthy range for your height. The NHS uses BMI as a screening tool to identify health risks associated with being underweight, overweight, or obese. To calculate your BMI, you need just two measurements: your weight in kilograms and your height in metres. The standard BMI formula divides your weight by your height squared. You can calculate it manually or use our free BMI calculator above for gradual improvement. Understanding your BMI is a useful first step in assessing your overall health, though it's important to know that BMI has limitations and should be considered alongside other health measures like waist circumference and lifestyle factors.
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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 defines healthy BMI ranges based on clinical evidence about health risk. According to NHS guidelines, the standard BMI categories are:
- Below 18.5: Underweight — may indicate insufficient weight for optimal health
- 18.5 to 24.9: Healthy weight — associated with lowest health risk for most adults
- 25.0 to 29.9: Overweight — associated with increased risk of weight-related health conditions
- 30.0 to 34.9: Obese (Class I) — significantly increased health risks
- 35.0 to 39.9: Obese (Class II) — high health risk
- 40.0 and above: Severely obese (Class III) — very high health risk
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds. For these groups, a healthy BMI range is 18.5 to 22.9, and overweight begins at 23.0. This is because these populations face higher cardiovascular and diabetes risks at lower BMI levels. NICE guidance emphasises that these adjusted thresholds better reflect health risk for these communities.
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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 Next Steps
If your BMI falls outside the healthy range, the NHS offers structured support through its weight management pathway. Your GP can assess your individual health and discuss whether you need support. The NHS pathway includes tier 1 (self-help and digital tools), tier 2 (primary care programmes), tier 3 (specialist weight management services), and tier 4 (bariatric surgery for severe obesity). Your GP can discuss which tier is appropriate for you based on your BMI, any weight-related health conditions, and your health goals. Even modest weight loss of 5–10% can significantly improve blood pressure, blood sugar control, and joint health. Use our free weight converter to track your measurements in stone, pounds, or kilograms as you progress.
- 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.
How do I calculate my BMI?
The BMI formula is: weight (kg) divided by height (metres) squared. For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. Use our free BMI calculator above to calculate instantly without doing the maths manually.
What's the difference between NHS BMI categories and other BMI charts?
The NHS BMI categories are based on UK clinical evidence and population health data. Other countries may use slightly different thresholds. The NHS also recommends lower thresholds for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels.
Why does the NHS recommend different BMI thresholds for some ethnic groups?
Research shows that South Asian, Chinese, Black African, and Black Caribbean populations have increased risk of type 2 diabetes and cardiovascular disease at lower BMI levels compared to European populations. The NHS adjusted thresholds reflect this evidence-based difference in health risk.
What should I do if my BMI is outside the healthy range?
Speak to your GP, who can assess your individual health and discuss options. The NHS offers weight management support through several tiers, from self-help resources and community programmes to specialist services. Your GP can advise on the best approach for you.
Are there limitations to BMI?
Yes. BMI doesn't distinguish between muscle and fat — athletes may have a high BMI but low body fat. It also doesn't account for where fat is stored or reflect bone density. Waist circumference and overall lifestyle are also important health indicators. Your GP can provide personalised advice.
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.