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 Can You Calculate BMI?
Calculating your BMI (Body Mass Index) is straightforward — it's a simple formula using your weight and height. The BMI formula divides your weight in kilograms by your height in metres squared. On this page, you'll find the exact calculation method, how to interpret your result using NHS categories, and important context about what BMI actually tells you about your health. You can also use our free BMI calculator above to get your result 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.
The BMI Formula and How to Calculate It
The BMI formula is: weight (kg) ÷ height (m)²
Here's how to calculate it step by step:
- Measure your height in centimetres and convert to metres (divide by 100). For example, 175cm = 1.75m
- Weigh yourself in kilograms
- Multiply your height in metres by itself. For example: 1.75 × 1.75 = 3.0625
- Divide your weight by this number. For example: 70kg ÷ 3.0625 = 22.9 BMI
According to NHS guidelines, a healthy BMI range is 18.5 to 24.9. The BMI categories UK adults should use are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese class I (30.0–34.9), obese class II (35.0–39.9), and severely obese (40.0+). Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower BMI thresholds recommended by the NHS.
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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
While BMI is a useful screening tool, it has important limitations. BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat. BMI also doesn't account for where fat is stored on your body. Waist circumference is equally important: the NHS recommends men keep waist measurement under 94cm (37 inches) and women under 80cm (31.5 inches). Age, ethnicity, and bone density also affect what a healthy weight means for you personally. Your GP can provide personalised advice about your BMI result and whether your weight poses any health risks. Use our free weight converter alongside the BMI calculator to check your measurements in different units.
- 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?
According to the NHS, a healthy BMI for most UK adults is between 18.5 and 24.9. However, adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds have different recommended thresholds — typically 18.5 to 22.9. Your GP can advise on what's healthy for your individual circumstances.
How do I convert my weight to metres for the BMI formula?
Divide your height in centimetres by 100. For example, if you're 168cm tall, divide 168 by 100 to get 1.68 metres. Then use 1.68 in the BMI formula: weight ÷ (1.68 × 1.68).
Is a BMI of 25 overweight?
Yes, according to NHS categories, a BMI of 25.0 to 29.9 falls into the overweight range. However, BMI alone doesn't determine health — waist circumference, fitness level, and overall health markers matter too. Speak to your GP about your individual health.
Can BMI be inaccurate?
Yes, BMI has limitations. It doesn't distinguish between muscle and fat, so muscular people may have a high BMI but be healthy. It also doesn't account for age, bone density, or where fat is stored. Waist measurement is a more accurate indicator of health risk for many people.
What should I do if my BMI is above 25?
If your BMI is in the overweight or obese range, speak to your GP. They can assess your overall health, discuss any health risks, and suggest support — which may include lifestyle changes, referral to weight management services, or other interventions depending on your circumstances. ```
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.