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 and takes just two measurements: your weight and height. BMI is a useful screening tool used by the NHS to assess whether adults are at a healthy weight, overweight, or obese. This guide explains the BMI formula, how to calculate your BMI, and what your result means according to UK health guidelines. You can also use our free BMI calculator above to find your BMI 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.
Understanding the BMI Formula and Ranges
The BMI formula is simple: divide your weight in kilograms by your height in metres squared. For example, if you weigh 70 kg and are 1.73 m tall, your BMI is 70 ÷ (1.73 × 1.73) = 23.4. According to NHS BMI guidance, the standard BMI range UK categories 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+). The overweight BMI threshold begins at 25.0. For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the NHS recommends lower thresholds, with healthy BMI starting at 18.5–22.9 and the overweight BMI threshold at 23.0, due to higher cardiovascular risk at lower BMI levels. Our free BMI calculator automatically sorts you into the correct category based on your ethnicity.
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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 Matters Beyond Numbers
While BMI is useful, it has important limitations. BMI does not distinguish between muscle and fat — athletes often have high BMI but low body fat. BMI also ignores where fat is stored; waist circumference is equally important for assessing health risk. The NHS recommends measuring your waist: over 94 cm (37 inches) for men and 80 cm (31.5 inches) for women indicates increased health risk. BMI is less accurate during pregnancy and in elderly people due to muscle loss. Your GP can provide personalised health advice beyond BMI alone, considering your overall health, family history, and any weight-related conditions. Use our weight converter to track your progress in the units that work best for you.
- 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 is 18.5 to 24.9 for most adults. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends 18.5 to 22.9. Use our BMI calculator to find your personal healthy weight range for your height.
How do I calculate my BMI if I use stone and pounds?
First convert your weight to kilograms: multiply stone by 6.35, then add pounds multiplied by 0.454. Then divide by your height in metres squared. Our free weight converter and BMI calculator handle this conversion instantly.
Is a BMI of 28 considered overweight?
Yes, a BMI of 28 falls in the overweight category (25.0–29.9). However, your GP may consider other factors like waist circumference, fitness level, and medical history before advising weight management.
Why do South Asian adults have different BMI thresholds?
Research shows South Asian, Chinese, Black African, and Black Caribbean adults develop weight-related health problems at lower BMI levels. The NHS recommends adjusted thresholds (18.5–22.9 for healthy weight) to account for this increased cardiovascular risk.
Can I rely on BMI alone to assess my health?
No. BMI is a screening tool but does not account for muscle mass, fitness, fat distribution, or medical conditions. Always discuss your weight and health with your GP for personalised guidance beyond BMI numbers alone.
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.