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 Stands For — What Does It Mean?
BMI stands for Body Mass Index — a measure of body fat based on height and weight. It's used by the NHS and healthcare professionals across the UK to screen for healthy weight ranges and assess health risk. BMI is calculated by dividing your weight in kilograms by your height in metres squared. While useful as a general screening tool, BMI has important limitations that your GP can explain in the context of your personal health. Use our free BMI calculator above to find your own BMI instantly.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 BMI Is Calculated and What the Ranges Mean
The BMI formula is simple: weight (kg) ÷ height (m)². For example, a person weighing 70kg and 1.73m tall would have a BMI of 23.4. The NHS uses standardised BMI categories UK to classify results:
- Below 18.5 = Underweight
- 18.5–24.9 = Healthy weight
- 25.0–29.9 = Overweight
- 30.0–34.9 = Obese (Class I)
- 35.0–39.9 = Obese (Class II)
- 40.0+ = Severely obese (Class III)
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — a healthy BMI for these groups starts at 18.5 but extends only to 22.9 rather than 24.9, because these populations face higher health risks at the same BMI levels. A healthy BMI range UK context matters: your GP can discuss what your individual BMI means for your health.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 What Else Matters
Although useful, the bmi limitations are important to understand. BMI does not distinguish between muscle and fat — athletes or very muscular individuals may have a high BMI but low body fat. BMI also ignores where fat is stored on your body; abdominal fat carries greater health risk than fat stored elsewhere. For older adults, pregnancy, or certain medical conditions, BMI may not be accurate. The NHS therefore recommends using BMI alongside waist circumference measurement: a waist above 94cm for men or 80cm for women indicates increased health risk. Your GP can assess your health holistically rather than relying on BMI alone. Try our weight converter to check your weight in different units alongside your BMI.
- 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 actually tell you about your health?
BMI tells you whether your weight falls within a healthy range for your height, according to NHS guidelines. However, it's a screening tool only — it doesn't measure body fat directly or account for muscle mass, bone density, or where fat is stored. Your GP will use BMI alongside other health markers like blood pressure, cholesterol, and waist measurement to assess your overall health.
Why does the NHS use different BMI thresholds for people of South Asian heritage?
Research shows that people of South Asian, Chinese, Black African, and Black Caribbean heritage develop weight-related health conditions like type 2 diabetes at lower BMI levels than European populations. The NHS therefore recommends lower BMI categories for these groups — a healthy BMI starts at 18.5 but only extends to 22.9, giving earlier intervention when needed.
Is a BMI of 25 considered overweight in the UK?
Yes. According to NHS guidelines, a BMI of 25.0–29.9 is classified as overweight. The overweight BMI threshold starts at 25 because research shows increased health risks above this point. However, BMI should not be your only concern — your waist circumference and overall health also matter.
Can BMI be inaccurate for athletes or very muscular people?
Yes. BMI cannot distinguish between muscle and fat, so athletes or very muscular individuals often have a higher BMI despite having low body fat. If you're very athletic, your GP may use additional measurements like waist circumference or body composition assessment rather than relying on BMI alone.
How do I calculate my own BMI?
The BMI formula is weight (kg) ÷ height (metres)². For example: 70kg ÷ (1.73²) = BMI 23.4. However, it's much easier to use our free BMI calculator at the top of this page — just enter your weight and height, and it calculates your BMI and tells you which NHS category you fall into instantly.
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.