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 Do You Calculate BMI Formula
BMI (Body Mass Index) is calculated using a straightforward formula that divides your weight by your height squared. The NHS uses BMI as a screening tool to assess whether an adult's weight is in a healthy range. This guide explains the exact BMI formula, how to work it out yourself, and what the NHS BMI categories mean for your health. Whether you use kilograms and metres or prefer UK measurements like stone and pounds, calculating your BMI takes just seconds. Try our free BMI calculator above to get your result 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.
BMI Formula and NHS Categories
The BMI formula is simple: weight (kg) ÷ height (metres) squared. For example, if you weigh 70kg and are 1.75 metres tall, your calculation is: 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy BMI range according to NHS guidance. The healthy BMI range is 18.5 to 24.9. The NHS also recognises five BMI categories: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25–29.9), obese class I (30–34.9), and obese class II or severely obese (35+). However, it's important to note that BMI has limitations—it doesn't distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. Use our free BMI calculator on this page to check your personal result instantly, and remember that individual circumstances vary.
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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 Support and When to Seek Help
If your BMI falls outside the healthy range, the NHS offers support through its weight management pathway. Your GP can provide personalised advice and may refer you to a local weight management service for dietary guidance, behaviour change support, or prescription weight loss medication. The nhs bmi guidance emphasises that even a modest 5% reduction in body weight can improve health outcomes. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower bmi range uk thresholds—starting at 23 for overweight and 27.5 for obese—because these groups face higher health risks at lower BMI levels. Your GP can assess your individual circumstances and discuss the most appropriate support 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's the difference between the BMI formula and BMI categories?
The BMI formula (weight ÷ height²) calculates a numerical score. NHS BMI categories then interpret that number—healthy weight is 18.5–24.9, overweight is 25–29.9, and obese is 30+. Use our BMI calculator to compute your score and see which category you fall into instantly.
Why does the NHS use BMI if it has limitations?
BMI is a quick, non-invasive screening tool. However, the NHS acknowledges its limitations—it doesn't account for muscle mass, bone density, or fat distribution. Waist measurement is also important. Your GP can assess your overall health picture, not just BMI.
Are BMI thresholds the same for everyone in the UK?
No. The NHS uses lower BMI thresholds for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher cardiovascular risk at lower BMI levels. Your GP can advise on thresholds relevant to your ethnicity and health status.
What should I do if my BMI is outside the healthy range?
Contact your GP, who can provide personalised advice and may refer you to a weight management service. The NHS offers support through its four-tier weight management pathway, from self-help tools to specialist services and medication.
Can I use the BMI formula with stone and pounds instead of kilograms?
Yes. Convert your weight to kilograms first (divide stone by 6.35 or multiply pounds by 0.454), then apply the formula. Our weight converter above makes this conversion instant, and the BMI calculator handles all measurements automatically.
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.