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 Determine Your BMI
Determining your BMI (body mass index) is straightforward — it's a measure of whether your weight falls into a healthy range for your height. The NHS uses BMI as a screening tool to assess health risk in adults. To determine your BMI, you need just two measurements: your weight and your height. You can calculate it manually using the BMI formula, or use our free BMI calculator above to get your result instantly. Understanding your BMI is the first step towards making informed decisions about 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.
How to Calculate and Understand Your BMI Range
The BMI formula is simple: weight in kilograms divided by height in metres squared (BMI = kg ÷ m²). For example, an adult weighing 70kg who is 1.75m tall would have a BMI of approximately 22.9, which falls in the healthy BMI range according to NHS guidelines.
The NHS BMI categories are:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight
- 25.0 to 29.9 — Overweight
- 30.0 to 34.9 — Obese (Class I)
- 35.0 to 39.9 — Obese (Class II)
- 40.0+ — Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the overweight BMI threshold is lower — a healthy range starts at 18.5 and extends to 22.9. This reflects higher health risks at lower BMI levels in these groups. Use our BMI calculator above to determine your personal BMI and see where you fall on the official BMI categories UK.
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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 Complementary Health Measures
While BMI is a useful screening tool, it has important BMI limitations. It does not distinguish between muscle and fat — a very muscular person may have a high BMI but low body fat. BMI also doesn't account for where fat is stored on your body; excess fat around the abdomen carries higher health risks than fat stored elsewhere. For this reason, the NHS recommends measuring waist circumference alongside BMI: men should aim for under 94cm (37 inches), and women under 80cm (31.5 inches).
For a more complete picture of your health, consider using our free weight converter to track changes in different units, and speak with your GP about your overall health risk profile rather than relying on BMI alone.
- 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?
A healthy BMI for most UK adults is between 18.5 and 24.9. For South Asian, Chinese, Black African, or Black Caribbean adults, the healthy range is 18.5 to 22.9 due to higher disease risk at lower BMI levels in these populations. You can determine your personal healthy BMI range using our calculator.
How do I calculate my BMI manually?
Use the BMI formula: weight in kg ÷ (height in metres)². For example, if you weigh 70kg and are 1.75m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = approximately 22.9 BMI. However, our free BMI calculator does this instantly and accurately.
What does it mean if my BMI is over 30?
A BMI of 30 or above falls into the obese category according to NHS classifications. This suggests an increased health risk for conditions like type 2 diabetes and heart disease. Your GP can assess your individual health and discuss next steps, which may include lifestyle changes or referral to weight management services.
Is BMI accurate for muscular or athletic people?
No — BMI does not distinguish between muscle and fat. A very muscular or athletic person may have a high BMI but low body fat percentage. If you're athletic, your GP or a healthcare professional can provide a more complete health assessment beyond BMI alone.
Why are BMI thresholds lower for some ethnic groups?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage have higher risks of type 2 diabetes and cardiovascular disease at the same BMI levels as other populations. The NHS therefore recommends lower thresholds for these groups to better identify health risk early.
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.