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 Calculator UK — Your Free Health Tool
A BMI calculator is a simple tool that measures your body mass index — a screening indicator of whether your weight falls within a healthy range for your height. MyWeightCheck's free BMI calculator is built specifically for UK adults and uses NHS guidance thresholds. It works instantly: enter your height and weight in stone, pounds, or kilograms, and get your BMI score plus clear information about what it means for your health. Unlike generic online tools, this UK health guide includes ethnicity-adjusted thresholds for South Asian, Chinese, Black African, and Black Caribbean adults, reflecting NHS recommendations that these groups face higher health risks at lower BMI levels.
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 a BMI Calculator Works and What Your Score Means
A BMI calculator uses a simple formula: your weight in kilograms divided by your height in metres squared. The result tells you whether your weight falls into a healthy range according to NHS guidance.
NHS BMI categories for UK adults:
- 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 and above = severely obese (Class III)
Important: BMI does not distinguish between muscle and fat, so athletes may have a high BMI but low body fat. BMI is also less accurate during pregnancy and in elderly people. Your weight management approach should always be personalised — your GP can provide guidance tailored to your health profile.
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.
Who Should Use a BMI Calculator and How to Access NHS Support
A BMI calculator is useful for any UK adult wanting to understand whether their weight falls within a healthy range. It's particularly valuable if you're beginning a weight management journey or monitoring health markers. Simply enter your height and current weight, and MyWeightCheck's calculator instantly shows your BMI and what it means according to NHS thresholds.
If your BMI suggests you're overweight or obese and you have health concerns, your GP can refer you to NHS weight management services. NHS guidance recommends weight loss at a rate of 0.5 to 1 kg per week for sustainable results. Many people find combining a BMI calculator with our free weight converter and progress tracker helpful for tracking progress over time.
- 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 a healthy BMI according to NHS guidance?
According to NHS guidelines, a healthy BMI for UK adults is between 18.5 and 24.9. However, for people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower threshold of 18.5 to 22.9, as these groups face higher health risks at lower BMI levels. Your GP can give you personalised advice about your individual healthy weight range.
Is BMI the only measure of health?
No. While a BMI calculator is a useful screening tool, it has limitations. BMI doesn't account for muscle mass versus fat, so athletes may have high BMI but low body fat. Waist circumference and overall fitness also matter. Your GP or healthcare professional can assess your health more comprehensively than BMI alone.
Can I use a BMI calculator if I'm pregnant?
BMI is less reliable during pregnancy because weight gain is expected and necessary for fetal health. If you're pregnant, speak with your GP or midwife about healthy weight management during pregnancy rather than relying on standard BMI categories.
How often should I use a BMI calculator to track progress?
Many people find it helpful to calculate BMI monthly rather than weekly, as weight naturally fluctuates daily due to water, food, and hormonal changes. Monthly checks give a clearer picture of trends. Combine your BMI calculator use with our free progress tracker for comprehensive weight management monitoring.
Where can I get NHS support if my BMI suggests overweight or obesity?
Contact your GP, who can assess your health and refer you to NHS weight management services if appropriate. The NHS offers tier 1 self-help programmes, tier 2 structured behaviour change programmes, and tier 3 specialist multidisciplinary services. Access varies by region. Your GP can guide you toward the right support for 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.