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
Calculate BMI Online Using NHS Guidelines
Calculating your BMI online is a quick way to understand your weight in relation to your height and check where you fall on the NHS health scale. BMI (body mass index) is a useful screening tool that helps identify whether you're at a healthy weight, overweight, or obese according to NHS standards. Using the free BMI calculator on this page, you can instantly see your BMI result and what it means for your health. However, it's important to understand that BMI has limitations — it doesn't account for muscle mass or where fat is stored — so it's just one part of the overall picture of your health.
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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 What They Mean
The NHS recognises five BMI categories that help determine your weight status and potential health risks. Understanding the BMI formula and your personal BMI range UK is essential for making informed health decisions.
- Healthy weight: BMI 18.5–24.9 — this is the target range the NHS recommends for most adults
- Overweight: BMI 25.0–29.9 — associated with increased health risks, though not yet in the obese category
- Obese (Class I): BMI 30.0–34.9 — increased risk of weight-related health conditions
- Obese (Class II): BMI 35.0–39.9 — higher health risks requiring lifestyle or medical intervention
- Severely obese (Class III): BMI 40.0+ — significantly elevated health risks
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds because these populations have higher cardiovascular and diabetes risk at lower BMI levels. For these groups, a healthy BMI is 18.5–22.9, and overweight begins at 23.0.
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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 and When to Seek Help
If your BMI calculator result shows you're overweight or obese, the NHS offers a structured weight management pathway. Start with your GP — they can assess your individual health, discuss lifestyle changes, and refer you to appropriate support services if needed. The NHS recommends a sustainable weight loss rate of 0.5–1 kg per week, achieved through a calorie deficit and increased physical activity.
For BMI 30 or above, or BMI 27–29 with weight-related conditions like type 2 diabetes or high blood pressure, your GP may refer you to tier 3 specialist weight management services. These services offer structured programmes, dietary support, and access to prescription weight loss medications where clinically appropriate. Use our free weight converter to track your progress in kg, stone, or lbs — whatever measurement you prefer.
- 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 NHS guidelines?
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is lower: 18.5 to 22.9. Your GP can advise on what's healthy for your individual circumstances.
Can I calculate my BMI online accurately?
Yes. Using the standard BMI formula — weight (kg) divided by height (metres) squared — gives an accurate screening result. Our free BMI calculator on this page uses this formula. However, BMI doesn't distinguish between muscle and fat, so it's a useful guide but not the complete picture of health.
What does BMI not tell me about my health?
BMI doesn't account for muscle mass (so athletes may have a high BMI but low body fat), where fat is stored (waist circumference matters), bone density, or fitness level. The NHS recommends also measuring waist circumference and discussing overall health with your GP.
When should I contact my GP about my BMI?
If your BMI calculator shows 25 or above, it's worth discussing with your GP, especially if you have weight-related health conditions. Your GP can assess whether lifestyle changes or additional support would help. Contact your GP if you're struggling to manage weight or have health concerns.
What's the difference between BMI limitations and BMI value?
Your BMI value is mathematically accurate based on height and weight, but BMI as a health tool has limitations — it doesn't measure body composition. This is why the NHS uses BMI alongside other assessments like waist circumference and clinical health evaluation for a complete picture.
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.